[v4] virtio_net: add page_pool support

[PATCH net-next v4 1/2] virtio_net: add page_pool support for buffer allocation

Posted by Vishwanath Seshagiri 4 days, 1 hour ago

Use page_pool for RX buffer allocation in mergeable and small buffer
modes to enable page recycling and avoid repeated page allocator calls.
skb_mark_for_recycle() enables page reuse in the network stack.

Big packets mode is unchanged because it uses page->private for linked
list chaining of multiple pages per buffer, which conflicts with
page_pool's internal use of page->private.

Implement conditional DMA premapping using virtqueue_dma_dev():
- When non-NULL (vhost, virtio-pci): use PP_FLAG_DMA_MAP with page_pool
  handling DMA mapping, submit via virtqueue_add_inbuf_premapped()
- When NULL (VDUSE, direct physical): page_pool handles allocation only,
  submit via virtqueue_add_inbuf_ctx()

This preserves the DMA premapping optimization from commit 31f3cd4e5756b
("virtio-net: rq submits premapped per-buffer") while adding page_pool
support as a prerequisite for future zero-copy features (devmem TCP,
io_uring ZCRX).

Page pools are created in probe and destroyed in remove (not open/close),
following existing driver behavior where RX buffers remain in virtqueues
across interface state changes.

Signed-off-by: Vishwanath Seshagiri <vishs@meta.com>
---
 drivers/net/Kconfig      |   1 +
 drivers/net/virtio_net.c | 351 ++++++++++++++++++++++-----------------
 2 files changed, 201 insertions(+), 151 deletions(-)

diff --git a/drivers/net/Kconfig b/drivers/net/Kconfig
index ac12eaf11755..f1e6b6b0a86f 100644
--- a/drivers/net/Kconfig
+++ b/drivers/net/Kconfig
@@ -450,6 +450,7 @@ config VIRTIO_NET
 	depends on VIRTIO
 	select NET_FAILOVER
 	select DIMLIB
+	select PAGE_POOL
 	help
 	  This is the virtual network driver for virtio.  It can be used with
 	  QEMU based VMMs (like KVM or Xen).  Say Y or M.
diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index db88dcaefb20..74c51e597c3f 100644
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c
@@ -26,6 +26,7 @@
 #include <net/netdev_rx_queue.h>
 #include <net/netdev_queues.h>
 #include <net/xdp_sock_drv.h>
+#include <net/page_pool/helpers.h>
 
 static int napi_weight = NAPI_POLL_WEIGHT;
 module_param(napi_weight, int, 0444);
@@ -359,6 +360,11 @@ struct receive_queue {
 	/* Page frag for packet buffer allocation. */
 	struct page_frag alloc_frag;
 
+	struct page_pool *page_pool;
+
+	/* True if page_pool handles DMA mapping via PP_FLAG_DMA_MAP */
+	bool use_page_pool_dma;
+
 	/* RX: fragments + linear part + virtio header */
 	struct scatterlist sg[MAX_SKB_FRAGS + 2];
 
@@ -521,11 +527,13 @@ static int virtnet_xdp_handler(struct bpf_prog *xdp_prog, struct xdp_buff *xdp,
 			       struct virtnet_rq_stats *stats);
 static void virtnet_receive_done(struct virtnet_info *vi, struct receive_queue *rq,
 				 struct sk_buff *skb, u8 flags);
-static struct sk_buff *virtnet_skb_append_frag(struct sk_buff *head_skb,
+static struct sk_buff *virtnet_skb_append_frag(struct receive_queue *rq,
+					       struct sk_buff *head_skb,
 					       struct sk_buff *curr_skb,
 					       struct page *page, void *buf,
 					       int len, int truesize);
 static void virtnet_xsk_completed(struct send_queue *sq, int num);
+static void free_unused_bufs(struct virtnet_info *vi);
 
 enum virtnet_xmit_type {
 	VIRTNET_XMIT_TYPE_SKB,
@@ -706,15 +714,24 @@ static struct page *get_a_page(struct receive_queue *rq, gfp_t gfp_mask)
 	return p;
 }
 
+static void virtnet_put_page(struct receive_queue *rq, struct page *page,
+			     bool allow_direct)
+{
+	if (page_pool_page_is_pp(page))
+		page_pool_put_page(rq->page_pool, page, -1, allow_direct);
+	else
+		put_page(page);
+}
+
 static void virtnet_rq_free_buf(struct virtnet_info *vi,
 				struct receive_queue *rq, void *buf)
 {
 	if (vi->mergeable_rx_bufs)
-		put_page(virt_to_head_page(buf));
+		virtnet_put_page(rq, virt_to_head_page(buf), false);
 	else if (vi->big_packets)
 		give_pages(rq, buf);
 	else
-		put_page(virt_to_head_page(buf));
+		virtnet_put_page(rq, virt_to_head_page(buf), false);
 }
 
 static void enable_rx_mode_work(struct virtnet_info *vi)
@@ -877,9 +894,12 @@ static struct sk_buff *page_to_skb(struct virtnet_info *vi,
 		if (unlikely(!skb))
 			return NULL;
 
-		page = (struct page *)page->private;
-		if (page)
-			give_pages(rq, page);
+		if (!rq->page_pool) {
+			page = (struct page *)page->private;
+			if (page)
+				give_pages(rq, page);
+		}
+
 		goto ok;
 	}
 
@@ -925,7 +945,7 @@ static struct sk_buff *page_to_skb(struct virtnet_info *vi,
 	hdr = skb_vnet_common_hdr(skb);
 	memcpy(hdr, hdr_p, hdr_len);
 	if (page_to_free)
-		put_page(page_to_free);
+		virtnet_put_page(rq, page_to_free, true);
 
 	return skb;
 }
@@ -965,93 +985,10 @@ static void virtnet_rq_unmap(struct receive_queue *rq, void *buf, u32 len)
 static void *virtnet_rq_get_buf(struct receive_queue *rq, u32 *len, void **ctx)
 {
 	struct virtnet_info *vi = rq->vq->vdev->priv;
-	void *buf;
-
-	BUG_ON(vi->big_packets && !vi->mergeable_rx_bufs);
-
-	buf = virtqueue_get_buf_ctx(rq->vq, len, ctx);
-	if (buf)
-		virtnet_rq_unmap(rq, buf, *len);
-
-	return buf;
-}
-
-static void virtnet_rq_init_one_sg(struct receive_queue *rq, void *buf, u32 len)
-{
-	struct virtnet_info *vi = rq->vq->vdev->priv;
-	struct virtnet_rq_dma *dma;
-	dma_addr_t addr;
-	u32 offset;
-	void *head;
-
-	BUG_ON(vi->big_packets && !vi->mergeable_rx_bufs);
-
-	head = page_address(rq->alloc_frag.page);
-
-	offset = buf - head;
-
-	dma = head;
-
-	addr = dma->addr - sizeof(*dma) + offset;
-
-	sg_init_table(rq->sg, 1);
-	sg_fill_dma(rq->sg, addr, len);
-}
-
-static void *virtnet_rq_alloc(struct receive_queue *rq, u32 size, gfp_t gfp)
-{
-	struct page_frag *alloc_frag = &rq->alloc_frag;
-	struct virtnet_info *vi = rq->vq->vdev->priv;
-	struct virtnet_rq_dma *dma;
-	void *buf, *head;
-	dma_addr_t addr;
 
 	BUG_ON(vi->big_packets && !vi->mergeable_rx_bufs);
 
-	head = page_address(alloc_frag->page);
-
-	dma = head;
-
-	/* new pages */
-	if (!alloc_frag->offset) {
-		if (rq->last_dma) {
-			/* Now, the new page is allocated, the last dma
-			 * will not be used. So the dma can be unmapped
-			 * if the ref is 0.
-			 */
-			virtnet_rq_unmap(rq, rq->last_dma, 0);
-			rq->last_dma = NULL;
-		}
-
-		dma->len = alloc_frag->size - sizeof(*dma);
-
-		addr = virtqueue_map_single_attrs(rq->vq, dma + 1,
-						  dma->len, DMA_FROM_DEVICE, 0);
-		if (virtqueue_map_mapping_error(rq->vq, addr))
-			return NULL;
-
-		dma->addr = addr;
-		dma->need_sync = virtqueue_map_need_sync(rq->vq, addr);
-
-		/* Add a reference to dma to prevent the entire dma from
-		 * being released during error handling. This reference
-		 * will be freed after the pages are no longer used.
-		 */
-		get_page(alloc_frag->page);
-		dma->ref = 1;
-		alloc_frag->offset = sizeof(*dma);
-
-		rq->last_dma = dma;
-	}
-
-	++dma->ref;
-
-	buf = head + alloc_frag->offset;
-
-	get_page(alloc_frag->page);
-	alloc_frag->offset += size;
-
-	return buf;
+	return virtqueue_get_buf_ctx(rq->vq, len, ctx);
 }
 
 static void virtnet_rq_unmap_free_buf(struct virtqueue *vq, void *buf)
@@ -1067,9 +1004,6 @@ static void virtnet_rq_unmap_free_buf(struct virtqueue *vq, void *buf)
 		return;
 	}
 
-	if (!vi->big_packets || vi->mergeable_rx_bufs)
-		virtnet_rq_unmap(rq, buf, 0);
-
 	virtnet_rq_free_buf(vi, rq, buf);
 }
 
@@ -1335,7 +1269,7 @@ static int xsk_append_merge_buffer(struct virtnet_info *vi,
 
 		truesize = len;
 
-		curr_skb  = virtnet_skb_append_frag(head_skb, curr_skb, page,
+		curr_skb  = virtnet_skb_append_frag(rq, head_skb, curr_skb, page,
 						    buf, len, truesize);
 		if (!curr_skb) {
 			put_page(page);
@@ -1771,7 +1705,7 @@ static int virtnet_xdp_xmit(struct net_device *dev,
 	return ret;
 }
 
-static void put_xdp_frags(struct xdp_buff *xdp)
+static void put_xdp_frags(struct receive_queue *rq, struct xdp_buff *xdp)
 {
 	struct skb_shared_info *shinfo;
 	struct page *xdp_page;
@@ -1781,7 +1715,7 @@ static void put_xdp_frags(struct xdp_buff *xdp)
 		shinfo = xdp_get_shared_info_from_buff(xdp);
 		for (i = 0; i < shinfo->nr_frags; i++) {
 			xdp_page = skb_frag_page(&shinfo->frags[i]);
-			put_page(xdp_page);
+			virtnet_put_page(rq, xdp_page, true);
 		}
 	}
 }
@@ -1873,7 +1807,7 @@ static struct page *xdp_linearize_page(struct net_device *dev,
 	if (page_off + *len + tailroom > PAGE_SIZE)
 		return NULL;
 
-	page = alloc_page(GFP_ATOMIC);
+	page = page_pool_alloc_pages(rq->page_pool, GFP_ATOMIC);
 	if (!page)
 		return NULL;
 
@@ -1897,7 +1831,7 @@ static struct page *xdp_linearize_page(struct net_device *dev,
 		off = buf - page_address(p);
 
 		if (check_mergeable_len(dev, ctx, buflen)) {
-			put_page(p);
+			virtnet_put_page(rq, p, true);
 			goto err_buf;
 		}
 
@@ -1905,21 +1839,21 @@ static struct page *xdp_linearize_page(struct net_device *dev,
 		 * is sending packet larger than the MTU.
 		 */
 		if ((page_off + buflen + tailroom) > PAGE_SIZE) {
-			put_page(p);
+			virtnet_put_page(rq, p, true);
 			goto err_buf;
 		}
 
 		memcpy(page_address(page) + page_off,
 		       page_address(p) + off, buflen);
 		page_off += buflen;
-		put_page(p);
+		virtnet_put_page(rq, p, true);
 	}
 
 	/* Headroom does not contribute to packet length */
 	*len = page_off - XDP_PACKET_HEADROOM;
 	return page;
 err_buf:
-	__free_pages(page, 0);
+	page_pool_put_page(rq->page_pool, page, -1, true);
 	return NULL;
 }
 
@@ -1996,7 +1930,7 @@ static struct sk_buff *receive_small_xdp(struct net_device *dev,
 			goto err_xdp;
 
 		buf = page_address(xdp_page);
-		put_page(page);
+		virtnet_put_page(rq, page, true);
 		page = xdp_page;
 	}
 
@@ -2028,13 +1962,15 @@ static struct sk_buff *receive_small_xdp(struct net_device *dev,
 	if (metasize)
 		skb_metadata_set(skb, metasize);
 
+	skb_mark_for_recycle(skb);
+
 	return skb;
 
 err_xdp:
 	u64_stats_inc(&stats->xdp_drops);
 err:
 	u64_stats_inc(&stats->drops);
-	put_page(page);
+	virtnet_put_page(rq, page, true);
 xdp_xmit:
 	return NULL;
 }
@@ -2082,12 +2018,14 @@ static struct sk_buff *receive_small(struct net_device *dev,
 	}
 
 	skb = receive_small_build_skb(vi, xdp_headroom, buf, len);
-	if (likely(skb))
+	if (likely(skb)) {
+		skb_mark_for_recycle(skb);
 		return skb;
+	}
 
 err:
 	u64_stats_inc(&stats->drops);
-	put_page(page);
+	virtnet_put_page(rq, page, true);
 	return NULL;
 }
 
@@ -2142,7 +2080,7 @@ static void mergeable_buf_free(struct receive_queue *rq, int num_buf,
 		}
 		u64_stats_add(&stats->bytes, len);
 		page = virt_to_head_page(buf);
-		put_page(page);
+		virtnet_put_page(rq, page, true);
 	}
 }
 
@@ -2253,7 +2191,7 @@ static int virtnet_build_xdp_buff_mrg(struct net_device *dev,
 		offset = buf - page_address(page);
 
 		if (check_mergeable_len(dev, ctx, len)) {
-			put_page(page);
+			virtnet_put_page(rq, page, true);
 			goto err;
 		}
 
@@ -2272,7 +2210,7 @@ static int virtnet_build_xdp_buff_mrg(struct net_device *dev,
 	return 0;
 
 err:
-	put_xdp_frags(xdp);
+	put_xdp_frags(rq, xdp);
 	return -EINVAL;
 }
 
@@ -2337,7 +2275,7 @@ static void *mergeable_xdp_get_buf(struct virtnet_info *vi,
 		if (*len + xdp_room > PAGE_SIZE)
 			return NULL;
 
-		xdp_page = alloc_page(GFP_ATOMIC);
+		xdp_page = page_pool_alloc_pages(rq->page_pool, GFP_ATOMIC);
 		if (!xdp_page)
 			return NULL;
 
@@ -2347,7 +2285,7 @@ static void *mergeable_xdp_get_buf(struct virtnet_info *vi,
 
 	*frame_sz = PAGE_SIZE;
 
-	put_page(*page);
+	virtnet_put_page(rq, *page, true);
 
 	*page = xdp_page;
 
@@ -2393,6 +2331,8 @@ static struct sk_buff *receive_mergeable_xdp(struct net_device *dev,
 		head_skb = build_skb_from_xdp_buff(dev, vi, &xdp, xdp_frags_truesz);
 		if (unlikely(!head_skb))
 			break;
+
+		skb_mark_for_recycle(head_skb);
 		return head_skb;
 
 	case XDP_TX:
@@ -2403,10 +2343,10 @@ static struct sk_buff *receive_mergeable_xdp(struct net_device *dev,
 		break;
 	}
 
-	put_xdp_frags(&xdp);
+	put_xdp_frags(rq, &xdp);
 
 err_xdp:
-	put_page(page);
+	virtnet_put_page(rq, page, true);
 	mergeable_buf_free(rq, num_buf, dev, stats);
 
 	u64_stats_inc(&stats->xdp_drops);
@@ -2414,7 +2354,8 @@ static struct sk_buff *receive_mergeable_xdp(struct net_device *dev,
 	return NULL;
 }
 
-static struct sk_buff *virtnet_skb_append_frag(struct sk_buff *head_skb,
+static struct sk_buff *virtnet_skb_append_frag(struct receive_queue *rq,
+					       struct sk_buff *head_skb,
 					       struct sk_buff *curr_skb,
 					       struct page *page, void *buf,
 					       int len, int truesize)
@@ -2446,7 +2387,7 @@ static struct sk_buff *virtnet_skb_append_frag(struct sk_buff *head_skb,
 
 	offset = buf - page_address(page);
 	if (skb_can_coalesce(curr_skb, num_skb_frags, page, offset)) {
-		put_page(page);
+		virtnet_put_page(rq, page, true);
 		skb_coalesce_rx_frag(curr_skb, num_skb_frags - 1,
 				     len, truesize);
 	} else {
@@ -2499,6 +2440,8 @@ static struct sk_buff *receive_mergeable(struct net_device *dev,
 
 	if (unlikely(!curr_skb))
 		goto err_skb;
+
+	skb_mark_for_recycle(head_skb);
 	while (--num_buf) {
 		buf = virtnet_rq_get_buf(rq, &len, &ctx);
 		if (unlikely(!buf)) {
@@ -2517,7 +2460,7 @@ static struct sk_buff *receive_mergeable(struct net_device *dev,
 			goto err_skb;
 
 		truesize = mergeable_ctx_to_truesize(ctx);
-		curr_skb  = virtnet_skb_append_frag(head_skb, curr_skb, page,
+		curr_skb  = virtnet_skb_append_frag(rq, head_skb, curr_skb, page,
 						    buf, len, truesize);
 		if (!curr_skb)
 			goto err_skb;
@@ -2527,7 +2470,7 @@ static struct sk_buff *receive_mergeable(struct net_device *dev,
 	return head_skb;
 
 err_skb:
-	put_page(page);
+	virtnet_put_page(rq, page, true);
 	mergeable_buf_free(rq, num_buf, dev, stats);
 
 err_buf:
@@ -2666,32 +2609,42 @@ static void receive_buf(struct virtnet_info *vi, struct receive_queue *rq,
 static int add_recvbuf_small(struct virtnet_info *vi, struct receive_queue *rq,
 			     gfp_t gfp)
 {
-	char *buf;
 	unsigned int xdp_headroom = virtnet_get_headroom(vi);
 	void *ctx = (void *)(unsigned long)xdp_headroom;
 	int len = vi->hdr_len + VIRTNET_RX_PAD + GOOD_PACKET_LEN + xdp_headroom;
+	unsigned int offset;
+	struct page *page;
+	dma_addr_t addr;
+	char *buf;
 	int err;
 
 	len = SKB_DATA_ALIGN(len) +
 	      SKB_DATA_ALIGN(sizeof(struct skb_shared_info));
 
-	if (unlikely(!skb_page_frag_refill(len, &rq->alloc_frag, gfp)))
-		return -ENOMEM;
-
-	buf = virtnet_rq_alloc(rq, len, gfp);
-	if (unlikely(!buf))
+	page = page_pool_alloc_frag(rq->page_pool, &offset, len, gfp);
+	if (unlikely(!page))
 		return -ENOMEM;
 
+	buf = page_address(page) + offset;
 	buf += VIRTNET_RX_PAD + xdp_headroom;
 
-	virtnet_rq_init_one_sg(rq, buf, vi->hdr_len + GOOD_PACKET_LEN);
+	if (rq->use_page_pool_dma) {
+		addr = page_pool_get_dma_addr(page) + offset;
+		addr += VIRTNET_RX_PAD + xdp_headroom;
 
-	err = virtqueue_add_inbuf_premapped(rq->vq, rq->sg, 1, buf, ctx, gfp);
-	if (err < 0) {
-		virtnet_rq_unmap(rq, buf, 0);
-		put_page(virt_to_head_page(buf));
+		sg_init_table(rq->sg, 1);
+		sg_fill_dma(rq->sg, addr, vi->hdr_len + GOOD_PACKET_LEN);
+		err = virtqueue_add_inbuf_premapped(rq->vq, rq->sg, 1,
+						    buf, ctx, gfp);
+	} else {
+		sg_init_one(rq->sg, buf, vi->hdr_len + GOOD_PACKET_LEN);
+		err = virtqueue_add_inbuf_ctx(rq->vq, rq->sg, 1,
+					      buf, ctx, gfp);
 	}
 
+	if (err < 0)
+		page_pool_put_page(rq->page_pool, virt_to_head_page(buf),
+				   -1, false);
 	return err;
 }
 
@@ -2764,13 +2717,15 @@ static unsigned int get_mergeable_buf_len(struct receive_queue *rq,
 static int add_recvbuf_mergeable(struct virtnet_info *vi,
 				 struct receive_queue *rq, gfp_t gfp)
 {
-	struct page_frag *alloc_frag = &rq->alloc_frag;
 	unsigned int headroom = virtnet_get_headroom(vi);
 	unsigned int tailroom = headroom ? sizeof(struct skb_shared_info) : 0;
 	unsigned int room = SKB_DATA_ALIGN(headroom + tailroom);
 	unsigned int len, hole;
-	void *ctx;
+	unsigned int offset;
+	struct page *page;
+	dma_addr_t addr;
 	char *buf;
+	void *ctx;
 	int err;
 
 	/* Extra tailroom is needed to satisfy XDP's assumption. This
@@ -2779,18 +2734,14 @@ static int add_recvbuf_mergeable(struct virtnet_info *vi,
 	 */
 	len = get_mergeable_buf_len(rq, &rq->mrg_avg_pkt_len, room);
 
-	if (unlikely(!skb_page_frag_refill(len + room, alloc_frag, gfp)))
-		return -ENOMEM;
-
-	if (!alloc_frag->offset && len + room + sizeof(struct virtnet_rq_dma) > alloc_frag->size)
-		len -= sizeof(struct virtnet_rq_dma);
-
-	buf = virtnet_rq_alloc(rq, len + room, gfp);
-	if (unlikely(!buf))
+	page = page_pool_alloc_frag(rq->page_pool, &offset, len + room, gfp);
+	if (unlikely(!page))
 		return -ENOMEM;
 
+	buf = page_address(page) + offset;
 	buf += headroom; /* advance address leaving hole at front of pkt */
-	hole = alloc_frag->size - alloc_frag->offset;
+
+	hole = PAGE_SIZE - (offset + len + room);
 	if (hole < len + room) {
 		/* To avoid internal fragmentation, if there is very likely not
 		 * enough space for another buffer, add the remaining space to
@@ -2800,18 +2751,27 @@ static int add_recvbuf_mergeable(struct virtnet_info *vi,
 		 */
 		if (!headroom)
 			len += hole;
-		alloc_frag->offset += hole;
 	}
 
-	virtnet_rq_init_one_sg(rq, buf, len);
-
 	ctx = mergeable_len_to_ctx(len + room, headroom);
-	err = virtqueue_add_inbuf_premapped(rq->vq, rq->sg, 1, buf, ctx, gfp);
-	if (err < 0) {
-		virtnet_rq_unmap(rq, buf, 0);
-		put_page(virt_to_head_page(buf));
+
+	if (rq->use_page_pool_dma) {
+		addr = page_pool_get_dma_addr(page) + offset;
+		addr += headroom;
+
+		sg_init_table(rq->sg, 1);
+		sg_fill_dma(rq->sg, addr, len);
+		err = virtqueue_add_inbuf_premapped(rq->vq, rq->sg, 1,
+						    buf, ctx, gfp);
+	} else {
+		sg_init_one(rq->sg, buf, len);
+		err = virtqueue_add_inbuf_ctx(rq->vq, rq->sg, 1,
+					      buf, ctx, gfp);
 	}
 
+	if (err < 0)
+		page_pool_put_page(rq->page_pool, virt_to_head_page(buf),
+				   -1, false);
 	return err;
 }
 
@@ -3128,7 +3088,10 @@ static int virtnet_enable_queue_pair(struct virtnet_info *vi, int qp_index)
 		return err;
 
 	err = xdp_rxq_info_reg_mem_model(&vi->rq[qp_index].xdp_rxq,
-					 MEM_TYPE_PAGE_SHARED, NULL);
+					 vi->rq[qp_index].page_pool ?
+						MEM_TYPE_PAGE_POOL :
+						MEM_TYPE_PAGE_SHARED,
+					 vi->rq[qp_index].page_pool);
 	if (err < 0)
 		goto err_xdp_reg_mem_model;
 
@@ -3168,6 +3131,81 @@ static void virtnet_update_settings(struct virtnet_info *vi)
 		vi->duplex = duplex;
 }
 
+static int virtnet_create_page_pools(struct virtnet_info *vi)
+{
+	int i, err;
+
+	if (!vi->mergeable_rx_bufs && vi->big_packets)
+		return 0;
+
+	for (i = 0; i < vi->max_queue_pairs; i++) {
+		struct receive_queue *rq = &vi->rq[i];
+		struct page_pool_params pp_params = { 0 };
+		struct device *dma_dev;
+
+		if (rq->page_pool)
+			continue;
+
+		if (rq->xsk_pool)
+			continue;
+
+		pp_params.order = 0;
+		pp_params.pool_size = virtqueue_get_vring_size(rq->vq);
+		pp_params.nid = dev_to_node(vi->vdev->dev.parent);
+		pp_params.netdev = vi->dev;
+		pp_params.napi = &rq->napi;
+
+		/* Check if backend supports DMA API (e.g., vhost, virtio-pci).
+		 * If so, use page_pool's DMA mapping for premapped buffers.
+		 * Otherwise (e.g., VDUSE), page_pool only handles allocation.
+		 */
+		dma_dev = virtqueue_dma_dev(rq->vq);
+		if (dma_dev) {
+			pp_params.dev = dma_dev;
+			pp_params.flags = PP_FLAG_DMA_MAP;
+			pp_params.dma_dir = DMA_FROM_DEVICE;
+			rq->use_page_pool_dma = true;
+		} else {
+			pp_params.dev = vi->vdev->dev.parent;
+			pp_params.flags = 0;
+			rq->use_page_pool_dma = false;
+		}
+
+		rq->page_pool = page_pool_create(&pp_params);
+		if (IS_ERR(rq->page_pool)) {
+			err = PTR_ERR(rq->page_pool);
+			rq->page_pool = NULL;
+			goto err_cleanup;
+		}
+	}
+	return 0;
+
+err_cleanup:
+	while (--i >= 0) {
+		struct receive_queue *rq = &vi->rq[i];
+
+		if (rq->page_pool) {
+			page_pool_destroy(rq->page_pool);
+			rq->page_pool = NULL;
+		}
+	}
+	return err;
+}
+
+static void virtnet_destroy_page_pools(struct virtnet_info *vi)
+{
+	int i;
+
+	for (i = 0; i < vi->max_queue_pairs; i++) {
+		struct receive_queue *rq = &vi->rq[i];
+
+		if (rq->page_pool) {
+			page_pool_destroy(rq->page_pool);
+			rq->page_pool = NULL;
+		}
+	}
+}
+
 static int virtnet_open(struct net_device *dev)
 {
 	struct virtnet_info *vi = netdev_priv(dev);
@@ -6441,10 +6479,8 @@ static int virtnet_find_vqs(struct virtnet_info *vi)
 		vi->rq[i].min_buf_len = mergeable_min_buf_len(vi, vi->rq[i].vq);
 		vi->sq[i].vq = vqs[txq2vq(i)];
 	}
-
 	/* run here: ret == 0. */
 
-
 err_find:
 	kfree(ctx);
 err_ctx:
@@ -6945,6 +6981,14 @@ static int virtnet_probe(struct virtio_device *vdev)
 			goto free;
 	}
 
+	/* Create page pools for receive queues.
+	 * Page pools are created at probe time so they can be used
+	 * with premapped DMA addresses throughout the device lifetime.
+	 */
+	err = virtnet_create_page_pools(vi);
+	if (err)
+		goto free_irq_moder;
+
 #ifdef CONFIG_SYSFS
 	if (vi->mergeable_rx_bufs)
 		dev->sysfs_rx_queue_group = &virtio_net_mrg_rx_group;
@@ -6958,7 +7002,7 @@ static int virtnet_probe(struct virtio_device *vdev)
 		vi->failover = net_failover_create(vi->dev);
 		if (IS_ERR(vi->failover)) {
 			err = PTR_ERR(vi->failover);
-			goto free_vqs;
+			goto free_page_pools;
 		}
 	}
 
@@ -7075,7 +7119,10 @@ static int virtnet_probe(struct virtio_device *vdev)
 	unregister_netdev(dev);
 free_failover:
 	net_failover_destroy(vi->failover);
-free_vqs:
+free_page_pools:
+	virtnet_destroy_page_pools(vi);
+free_irq_moder:
+	virtnet_free_irq_moder(vi);
 	virtio_reset_device(vdev);
 	free_receive_page_frags(vi);
 	virtnet_del_vqs(vi);
@@ -7104,6 +7151,8 @@ static void remove_vq_common(struct virtnet_info *vi)
 
 	free_receive_page_frags(vi);
 
+	virtnet_destroy_page_pools(vi);
+
 	virtnet_del_vqs(vi);
 }
 
-- 
2.47.3

Re: [PATCH net-next v4 1/2] virtio_net: add page_pool support for buffer allocation

Posted by Michael S. Tsirkin 3 days, 16 hours ago

On Wed, Feb 04, 2026 at 11:36:16AM -0800, Vishwanath Seshagiri wrote:
> Use page_pool for RX buffer allocation in mergeable and small buffer
> modes to enable page recycling and avoid repeated page allocator calls.
> skb_mark_for_recycle() enables page reuse in the network stack.
> 
> Big packets mode is unchanged because it uses page->private for linked
> list chaining of multiple pages per buffer, which conflicts with
> page_pool's internal use of page->private.
> 
> Implement conditional DMA premapping using virtqueue_dma_dev():
> - When non-NULL (vhost, virtio-pci): use PP_FLAG_DMA_MAP with page_pool
>   handling DMA mapping, submit via virtqueue_add_inbuf_premapped()
> - When NULL (VDUSE, direct physical): page_pool handles allocation only,
>   submit via virtqueue_add_inbuf_ctx()
> 
> This preserves the DMA premapping optimization from commit 31f3cd4e5756b
> ("virtio-net: rq submits premapped per-buffer") while adding page_pool
> support as a prerequisite for future zero-copy features (devmem TCP,
> io_uring ZCRX).
> 
> Page pools are created in probe and destroyed in remove (not open/close),
> following existing driver behavior where RX buffers remain in virtqueues
> across interface state changes.
> 
> Signed-off-by: Vishwanath Seshagiri <vishs@meta.com>
> ---
>  drivers/net/Kconfig      |   1 +
>  drivers/net/virtio_net.c | 351 ++++++++++++++++++++++-----------------
>  2 files changed, 201 insertions(+), 151 deletions(-)
> 
> diff --git a/drivers/net/Kconfig b/drivers/net/Kconfig
> index ac12eaf11755..f1e6b6b0a86f 100644
> --- a/drivers/net/Kconfig
> +++ b/drivers/net/Kconfig
> @@ -450,6 +450,7 @@ config VIRTIO_NET
>  	depends on VIRTIO
>  	select NET_FAILOVER
>  	select DIMLIB
> +	select PAGE_POOL
>  	help
>  	  This is the virtual network driver for virtio.  It can be used with
>  	  QEMU based VMMs (like KVM or Xen).  Say Y or M.
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index db88dcaefb20..74c51e597c3f 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -26,6 +26,7 @@
>  #include <net/netdev_rx_queue.h>
>  #include <net/netdev_queues.h>
>  #include <net/xdp_sock_drv.h>
> +#include <net/page_pool/helpers.h>
>  
>  static int napi_weight = NAPI_POLL_WEIGHT;
>  module_param(napi_weight, int, 0444);
> @@ -359,6 +360,11 @@ struct receive_queue {
>  	/* Page frag for packet buffer allocation. */
>  	struct page_frag alloc_frag;
>  
> +	struct page_pool *page_pool;
> +
> +	/* True if page_pool handles DMA mapping via PP_FLAG_DMA_MAP */
> +	bool use_page_pool_dma;
> +
>  	/* RX: fragments + linear part + virtio header */
>  	struct scatterlist sg[MAX_SKB_FRAGS + 2];
>  
> @@ -521,11 +527,13 @@ static int virtnet_xdp_handler(struct bpf_prog *xdp_prog, struct xdp_buff *xdp,
>  			       struct virtnet_rq_stats *stats);
>  static void virtnet_receive_done(struct virtnet_info *vi, struct receive_queue *rq,
>  				 struct sk_buff *skb, u8 flags);
> -static struct sk_buff *virtnet_skb_append_frag(struct sk_buff *head_skb,
> +static struct sk_buff *virtnet_skb_append_frag(struct receive_queue *rq,
> +					       struct sk_buff *head_skb,
>  					       struct sk_buff *curr_skb,
>  					       struct page *page, void *buf,
>  					       int len, int truesize);
>  static void virtnet_xsk_completed(struct send_queue *sq, int num);
> +static void free_unused_bufs(struct virtnet_info *vi);
>  
>  enum virtnet_xmit_type {
>  	VIRTNET_XMIT_TYPE_SKB,
> @@ -706,15 +714,24 @@ static struct page *get_a_page(struct receive_queue *rq, gfp_t gfp_mask)
>  	return p;
>  }
>  
> +static void virtnet_put_page(struct receive_queue *rq, struct page *page,
> +			     bool allow_direct)
> +{
> +	if (page_pool_page_is_pp(page))
> +		page_pool_put_page(rq->page_pool, page, -1, allow_direct);
> +	else
> +		put_page(page);
> +}
> +
>  static void virtnet_rq_free_buf(struct virtnet_info *vi,
>  				struct receive_queue *rq, void *buf)
>  {
>  	if (vi->mergeable_rx_bufs)
> -		put_page(virt_to_head_page(buf));
> +		virtnet_put_page(rq, virt_to_head_page(buf), false);
>  	else if (vi->big_packets)
>  		give_pages(rq, buf);
>  	else
> -		put_page(virt_to_head_page(buf));
> +		virtnet_put_page(rq, virt_to_head_page(buf), false);
>  }
>  
>  static void enable_rx_mode_work(struct virtnet_info *vi)
> @@ -877,9 +894,12 @@ static struct sk_buff *page_to_skb(struct virtnet_info *vi,
>  		if (unlikely(!skb))
>  			return NULL;
>  
> -		page = (struct page *)page->private;
> -		if (page)
> -			give_pages(rq, page);
> +		if (!rq->page_pool) {

I think this is ok because big_packets is exactly when this happens.
but it is confusing that the conditions on free and alloc are
written differently. A comment with an explanation, at least?


> +			page = (struct page *)page->private;
> +			if (page)
> +				give_pages(rq, page);
> +		}
> +
>  		goto ok;
>  	}
>  
> @@ -925,7 +945,7 @@ static struct sk_buff *page_to_skb(struct virtnet_info *vi,
>  	hdr = skb_vnet_common_hdr(skb);
>  	memcpy(hdr, hdr_p, hdr_len);
>  	if (page_to_free)
> -		put_page(page_to_free);
> +		virtnet_put_page(rq, page_to_free, true);
>  
>  	return skb;
>  }
> @@ -965,93 +985,10 @@ static void virtnet_rq_unmap(struct receive_queue *rq, void *buf, u32 len)
>  static void *virtnet_rq_get_buf(struct receive_queue *rq, u32 *len, void **ctx)
>  {
>  	struct virtnet_info *vi = rq->vq->vdev->priv;
> -	void *buf;
> -
> -	BUG_ON(vi->big_packets && !vi->mergeable_rx_bufs);
> -
> -	buf = virtqueue_get_buf_ctx(rq->vq, len, ctx);
> -	if (buf)
> -		virtnet_rq_unmap(rq, buf, *len);
> -
> -	return buf;
> -}
> -
> -static void virtnet_rq_init_one_sg(struct receive_queue *rq, void *buf, u32 len)
> -{
> -	struct virtnet_info *vi = rq->vq->vdev->priv;
> -	struct virtnet_rq_dma *dma;
> -	dma_addr_t addr;
> -	u32 offset;
> -	void *head;
> -
> -	BUG_ON(vi->big_packets && !vi->mergeable_rx_bufs);
> -
> -	head = page_address(rq->alloc_frag.page);
> -
> -	offset = buf - head;
> -
> -	dma = head;
> -
> -	addr = dma->addr - sizeof(*dma) + offset;
> -
> -	sg_init_table(rq->sg, 1);
> -	sg_fill_dma(rq->sg, addr, len);
> -}
> -
> -static void *virtnet_rq_alloc(struct receive_queue *rq, u32 size, gfp_t gfp)
> -{
> -	struct page_frag *alloc_frag = &rq->alloc_frag;
> -	struct virtnet_info *vi = rq->vq->vdev->priv;
> -	struct virtnet_rq_dma *dma;
> -	void *buf, *head;
> -	dma_addr_t addr;
>  
>  	BUG_ON(vi->big_packets && !vi->mergeable_rx_bufs);
>  
> -	head = page_address(alloc_frag->page);
> -
> -	dma = head;
> -
> -	/* new pages */
> -	if (!alloc_frag->offset) {
> -		if (rq->last_dma) {
> -			/* Now, the new page is allocated, the last dma
> -			 * will not be used. So the dma can be unmapped
> -			 * if the ref is 0.
> -			 */
> -			virtnet_rq_unmap(rq, rq->last_dma, 0);
> -			rq->last_dma = NULL;
> -		}
> -
> -		dma->len = alloc_frag->size - sizeof(*dma);
> -
> -		addr = virtqueue_map_single_attrs(rq->vq, dma + 1,
> -						  dma->len, DMA_FROM_DEVICE, 0);
> -		if (virtqueue_map_mapping_error(rq->vq, addr))
> -			return NULL;
> -
> -		dma->addr = addr;
> -		dma->need_sync = virtqueue_map_need_sync(rq->vq, addr);

it gives me pause that this patch never does sync.
don't you need page_pool_dma_sync_for_cpu somewhere?



> -
> -		/* Add a reference to dma to prevent the entire dma from
> -		 * being released during error handling. This reference
> -		 * will be freed after the pages are no longer used.
> -		 */
> -		get_page(alloc_frag->page);
> -		dma->ref = 1;
> -		alloc_frag->offset = sizeof(*dma);
> -
> -		rq->last_dma = dma;
> -	}
> -
> -	++dma->ref;
> -
> -	buf = head + alloc_frag->offset;
> -
> -	get_page(alloc_frag->page);
> -	alloc_frag->offset += size;
> -
> -	return buf;
> +	return virtqueue_get_buf_ctx(rq->vq, len, ctx);
>  }
>  
>  static void virtnet_rq_unmap_free_buf(struct virtqueue *vq, void *buf)
> @@ -1067,9 +1004,6 @@ static void virtnet_rq_unmap_free_buf(struct virtqueue *vq, void *buf)
>  		return;
>  	}
>  
> -	if (!vi->big_packets || vi->mergeable_rx_bufs)
> -		virtnet_rq_unmap(rq, buf, 0);
> -
>  	virtnet_rq_free_buf(vi, rq, buf);
>  }
>  
> @@ -1335,7 +1269,7 @@ static int xsk_append_merge_buffer(struct virtnet_info *vi,
>  
>  		truesize = len;
>  
> -		curr_skb  = virtnet_skb_append_frag(head_skb, curr_skb, page,
> +		curr_skb  = virtnet_skb_append_frag(rq, head_skb, curr_skb, page,
>  						    buf, len, truesize);
>  		if (!curr_skb) {
>  			put_page(page);
> @@ -1771,7 +1705,7 @@ static int virtnet_xdp_xmit(struct net_device *dev,
>  	return ret;
>  }
>  
> -static void put_xdp_frags(struct xdp_buff *xdp)
> +static void put_xdp_frags(struct receive_queue *rq, struct xdp_buff *xdp)
>  {
>  	struct skb_shared_info *shinfo;
>  	struct page *xdp_page;
> @@ -1781,7 +1715,7 @@ static void put_xdp_frags(struct xdp_buff *xdp)
>  		shinfo = xdp_get_shared_info_from_buff(xdp);
>  		for (i = 0; i < shinfo->nr_frags; i++) {
>  			xdp_page = skb_frag_page(&shinfo->frags[i]);
> -			put_page(xdp_page);
> +			virtnet_put_page(rq, xdp_page, true);
>  		}
>  	}
>  }
> @@ -1873,7 +1807,7 @@ static struct page *xdp_linearize_page(struct net_device *dev,
>  	if (page_off + *len + tailroom > PAGE_SIZE)
>  		return NULL;
>  
> -	page = alloc_page(GFP_ATOMIC);
> +	page = page_pool_alloc_pages(rq->page_pool, GFP_ATOMIC);
>  	if (!page)
>  		return NULL;
>  
> @@ -1897,7 +1831,7 @@ static struct page *xdp_linearize_page(struct net_device *dev,
>  		off = buf - page_address(p);
>  
>  		if (check_mergeable_len(dev, ctx, buflen)) {
> -			put_page(p);
> +			virtnet_put_page(rq, p, true);
>  			goto err_buf;
>  		}
>  
> @@ -1905,21 +1839,21 @@ static struct page *xdp_linearize_page(struct net_device *dev,
>  		 * is sending packet larger than the MTU.
>  		 */
>  		if ((page_off + buflen + tailroom) > PAGE_SIZE) {
> -			put_page(p);
> +			virtnet_put_page(rq, p, true);
>  			goto err_buf;
>  		}
>  
>  		memcpy(page_address(page) + page_off,
>  		       page_address(p) + off, buflen);
>  		page_off += buflen;
> -		put_page(p);
> +		virtnet_put_page(rq, p, true);
>  	}
>  
>  	/* Headroom does not contribute to packet length */
>  	*len = page_off - XDP_PACKET_HEADROOM;
>  	return page;
>  err_buf:
> -	__free_pages(page, 0);
> +	page_pool_put_page(rq->page_pool, page, -1, true);
>  	return NULL;
>  }
>  
> @@ -1996,7 +1930,7 @@ static struct sk_buff *receive_small_xdp(struct net_device *dev,
>  			goto err_xdp;
>  
>  		buf = page_address(xdp_page);
> -		put_page(page);
> +		virtnet_put_page(rq, page, true);
>  		page = xdp_page;
>  	}
>  
> @@ -2028,13 +1962,15 @@ static struct sk_buff *receive_small_xdp(struct net_device *dev,
>  	if (metasize)
>  		skb_metadata_set(skb, metasize);
>  
> +	skb_mark_for_recycle(skb);
> +
>  	return skb;
>  
>  err_xdp:
>  	u64_stats_inc(&stats->xdp_drops);
>  err:
>  	u64_stats_inc(&stats->drops);
> -	put_page(page);
> +	virtnet_put_page(rq, page, true);
>  xdp_xmit:
>  	return NULL;
>  }
> @@ -2082,12 +2018,14 @@ static struct sk_buff *receive_small(struct net_device *dev,
>  	}
>  
>  	skb = receive_small_build_skb(vi, xdp_headroom, buf, len);
> -	if (likely(skb))
> +	if (likely(skb)) {
> +		skb_mark_for_recycle(skb);
>  		return skb;
> +	}
>  
>  err:
>  	u64_stats_inc(&stats->drops);
> -	put_page(page);
> +	virtnet_put_page(rq, page, true);
>  	return NULL;
>  }
>  
> @@ -2142,7 +2080,7 @@ static void mergeable_buf_free(struct receive_queue *rq, int num_buf,
>  		}
>  		u64_stats_add(&stats->bytes, len);
>  		page = virt_to_head_page(buf);
> -		put_page(page);
> +		virtnet_put_page(rq, page, true);
>  	}
>  }
>  
> @@ -2253,7 +2191,7 @@ static int virtnet_build_xdp_buff_mrg(struct net_device *dev,
>  		offset = buf - page_address(page);
>  
>  		if (check_mergeable_len(dev, ctx, len)) {
> -			put_page(page);
> +			virtnet_put_page(rq, page, true);
>  			goto err;
>  		}
>  
> @@ -2272,7 +2210,7 @@ static int virtnet_build_xdp_buff_mrg(struct net_device *dev,
>  	return 0;
>  
>  err:
> -	put_xdp_frags(xdp);
> +	put_xdp_frags(rq, xdp);
>  	return -EINVAL;
>  }
>  
> @@ -2337,7 +2275,7 @@ static void *mergeable_xdp_get_buf(struct virtnet_info *vi,
>  		if (*len + xdp_room > PAGE_SIZE)
>  			return NULL;
>  
> -		xdp_page = alloc_page(GFP_ATOMIC);
> +		xdp_page = page_pool_alloc_pages(rq->page_pool, GFP_ATOMIC);
>  		if (!xdp_page)
>  			return NULL;
>  
> @@ -2347,7 +2285,7 @@ static void *mergeable_xdp_get_buf(struct virtnet_info *vi,
>  
>  	*frame_sz = PAGE_SIZE;
>  
> -	put_page(*page);
> +	virtnet_put_page(rq, *page, true);
>  
>  	*page = xdp_page;
>  
> @@ -2393,6 +2331,8 @@ static struct sk_buff *receive_mergeable_xdp(struct net_device *dev,
>  		head_skb = build_skb_from_xdp_buff(dev, vi, &xdp, xdp_frags_truesz);
>  		if (unlikely(!head_skb))
>  			break;
> +
> +		skb_mark_for_recycle(head_skb);
>  		return head_skb;
>  
>  	case XDP_TX:
> @@ -2403,10 +2343,10 @@ static struct sk_buff *receive_mergeable_xdp(struct net_device *dev,
>  		break;
>  	}
>  
> -	put_xdp_frags(&xdp);
> +	put_xdp_frags(rq, &xdp);
>  
>  err_xdp:
> -	put_page(page);
> +	virtnet_put_page(rq, page, true);
>  	mergeable_buf_free(rq, num_buf, dev, stats);
>  
>  	u64_stats_inc(&stats->xdp_drops);
> @@ -2414,7 +2354,8 @@ static struct sk_buff *receive_mergeable_xdp(struct net_device *dev,
>  	return NULL;
>  }
>  
> -static struct sk_buff *virtnet_skb_append_frag(struct sk_buff *head_skb,
> +static struct sk_buff *virtnet_skb_append_frag(struct receive_queue *rq,
> +					       struct sk_buff *head_skb,
>  					       struct sk_buff *curr_skb,
>  					       struct page *page, void *buf,
>  					       int len, int truesize)
> @@ -2446,7 +2387,7 @@ static struct sk_buff *virtnet_skb_append_frag(struct sk_buff *head_skb,
>  
>  	offset = buf - page_address(page);
>  	if (skb_can_coalesce(curr_skb, num_skb_frags, page, offset)) {
> -		put_page(page);
> +		virtnet_put_page(rq, page, true);
>  		skb_coalesce_rx_frag(curr_skb, num_skb_frags - 1,
>  				     len, truesize);
>  	} else {
> @@ -2499,6 +2440,8 @@ static struct sk_buff *receive_mergeable(struct net_device *dev,
>  
>  	if (unlikely(!curr_skb))
>  		goto err_skb;
> +
> +	skb_mark_for_recycle(head_skb);
>  	while (--num_buf) {
>  		buf = virtnet_rq_get_buf(rq, &len, &ctx);
>  		if (unlikely(!buf)) {
> @@ -2517,7 +2460,7 @@ static struct sk_buff *receive_mergeable(struct net_device *dev,
>  			goto err_skb;
>  
>  		truesize = mergeable_ctx_to_truesize(ctx);
> -		curr_skb  = virtnet_skb_append_frag(head_skb, curr_skb, page,
> +		curr_skb  = virtnet_skb_append_frag(rq, head_skb, curr_skb, page,
>  						    buf, len, truesize);
>  		if (!curr_skb)
>  			goto err_skb;
> @@ -2527,7 +2470,7 @@ static struct sk_buff *receive_mergeable(struct net_device *dev,
>  	return head_skb;
>  
>  err_skb:
> -	put_page(page);
> +	virtnet_put_page(rq, page, true);
>  	mergeable_buf_free(rq, num_buf, dev, stats);
>  
>  err_buf:
> @@ -2666,32 +2609,42 @@ static void receive_buf(struct virtnet_info *vi, struct receive_queue *rq,
>  static int add_recvbuf_small(struct virtnet_info *vi, struct receive_queue *rq,
>  			     gfp_t gfp)
>  {
> -	char *buf;
>  	unsigned int xdp_headroom = virtnet_get_headroom(vi);
>  	void *ctx = (void *)(unsigned long)xdp_headroom;
>  	int len = vi->hdr_len + VIRTNET_RX_PAD + GOOD_PACKET_LEN + xdp_headroom;
> +	unsigned int offset;
> +	struct page *page;
> +	dma_addr_t addr;
> +	char *buf;
>  	int err;
>  
>  	len = SKB_DATA_ALIGN(len) +
>  	      SKB_DATA_ALIGN(sizeof(struct skb_shared_info));
>  
> -	if (unlikely(!skb_page_frag_refill(len, &rq->alloc_frag, gfp)))
> -		return -ENOMEM;
> -
> -	buf = virtnet_rq_alloc(rq, len, gfp);
> -	if (unlikely(!buf))
> +	page = page_pool_alloc_frag(rq->page_pool, &offset, len, gfp);
> +	if (unlikely(!page))
>  		return -ENOMEM;
>  
> +	buf = page_address(page) + offset;
>  	buf += VIRTNET_RX_PAD + xdp_headroom;
>  
> -	virtnet_rq_init_one_sg(rq, buf, vi->hdr_len + GOOD_PACKET_LEN);
> +	if (rq->use_page_pool_dma) {
> +		addr = page_pool_get_dma_addr(page) + offset;
> +		addr += VIRTNET_RX_PAD + xdp_headroom;
>  
> -	err = virtqueue_add_inbuf_premapped(rq->vq, rq->sg, 1, buf, ctx, gfp);
> -	if (err < 0) {
> -		virtnet_rq_unmap(rq, buf, 0);
> -		put_page(virt_to_head_page(buf));
> +		sg_init_table(rq->sg, 1);
> +		sg_fill_dma(rq->sg, addr, vi->hdr_len + GOOD_PACKET_LEN);
> +		err = virtqueue_add_inbuf_premapped(rq->vq, rq->sg, 1,
> +						    buf, ctx, gfp);
> +	} else {
> +		sg_init_one(rq->sg, buf, vi->hdr_len + GOOD_PACKET_LEN);
> +		err = virtqueue_add_inbuf_ctx(rq->vq, rq->sg, 1,
> +					      buf, ctx, gfp);
>  	}
>  
> +	if (err < 0)
> +		page_pool_put_page(rq->page_pool, virt_to_head_page(buf),
> +				   -1, false);
>  	return err;
>  }
>  
> @@ -2764,13 +2717,15 @@ static unsigned int get_mergeable_buf_len(struct receive_queue *rq,
>  static int add_recvbuf_mergeable(struct virtnet_info *vi,
>  				 struct receive_queue *rq, gfp_t gfp)
>  {
> -	struct page_frag *alloc_frag = &rq->alloc_frag;
>  	unsigned int headroom = virtnet_get_headroom(vi);
>  	unsigned int tailroom = headroom ? sizeof(struct skb_shared_info) : 0;
>  	unsigned int room = SKB_DATA_ALIGN(headroom + tailroom);
>  	unsigned int len, hole;
> -	void *ctx;
> +	unsigned int offset;
> +	struct page *page;
> +	dma_addr_t addr;
>  	char *buf;
> +	void *ctx;
>  	int err;
>  
>  	/* Extra tailroom is needed to satisfy XDP's assumption. This
> @@ -2779,18 +2734,14 @@ static int add_recvbuf_mergeable(struct virtnet_info *vi,
>  	 */
>  	len = get_mergeable_buf_len(rq, &rq->mrg_avg_pkt_len, room);
>  
> -	if (unlikely(!skb_page_frag_refill(len + room, alloc_frag, gfp)))
> -		return -ENOMEM;
> -
> -	if (!alloc_frag->offset && len + room + sizeof(struct virtnet_rq_dma) > alloc_frag->size)
> -		len -= sizeof(struct virtnet_rq_dma);
> -
> -	buf = virtnet_rq_alloc(rq, len + room, gfp);
> -	if (unlikely(!buf))
> +	page = page_pool_alloc_frag(rq->page_pool, &offset, len + room, gfp);
> +	if (unlikely(!page))
>  		return -ENOMEM;
>  
> +	buf = page_address(page) + offset;
>  	buf += headroom; /* advance address leaving hole at front of pkt */
> -	hole = alloc_frag->size - alloc_frag->offset;
> +
> +	hole = PAGE_SIZE - (offset + len + room);
>  	if (hole < len + room) {
>  		/* To avoid internal fragmentation, if there is very likely not
>  		 * enough space for another buffer, add the remaining space to
> @@ -2800,18 +2751,27 @@ static int add_recvbuf_mergeable(struct virtnet_info *vi,
>  		 */
>  		if (!headroom)
>  			len += hole;
> -		alloc_frag->offset += hole;

Hmm. All these allocations are tricky.
So we used to advance offset by hole but with page pool api
what advances pool->frag_offset? If nothing will not the next
small allocation reuse the space and overlap the buffer?


>  	}
>  
> -	virtnet_rq_init_one_sg(rq, buf, len);
> -
>  	ctx = mergeable_len_to_ctx(len + room, headroom);
> -	err = virtqueue_add_inbuf_premapped(rq->vq, rq->sg, 1, buf, ctx, gfp);
> -	if (err < 0) {
> -		virtnet_rq_unmap(rq, buf, 0);
> -		put_page(virt_to_head_page(buf));
> +
> +	if (rq->use_page_pool_dma) {
> +		addr = page_pool_get_dma_addr(page) + offset;
> +		addr += headroom;
> +
> +		sg_init_table(rq->sg, 1);
> +		sg_fill_dma(rq->sg, addr, len);
> +		err = virtqueue_add_inbuf_premapped(rq->vq, rq->sg, 1,
> +						    buf, ctx, gfp);
> +	} else {
> +		sg_init_one(rq->sg, buf, len);
> +		err = virtqueue_add_inbuf_ctx(rq->vq, rq->sg, 1,
> +					      buf, ctx, gfp);
>  	}
>  
> +	if (err < 0)
> +		page_pool_put_page(rq->page_pool, virt_to_head_page(buf),
> +				   -1, false);
>  	return err;
>  }
>  
> @@ -3128,7 +3088,10 @@ static int virtnet_enable_queue_pair(struct virtnet_info *vi, int qp_index)
>  		return err;
>  
>  	err = xdp_rxq_info_reg_mem_model(&vi->rq[qp_index].xdp_rxq,
> -					 MEM_TYPE_PAGE_SHARED, NULL);
> +					 vi->rq[qp_index].page_pool ?
> +						MEM_TYPE_PAGE_POOL :
> +						MEM_TYPE_PAGE_SHARED,
> +					 vi->rq[qp_index].page_pool);
>  	if (err < 0)
>  		goto err_xdp_reg_mem_model;
>  
> @@ -3168,6 +3131,81 @@ static void virtnet_update_settings(struct virtnet_info *vi)
>  		vi->duplex = duplex;
>  }
>  
> +static int virtnet_create_page_pools(struct virtnet_info *vi)
> +{
> +	int i, err;
> +
> +	if (!vi->mergeable_rx_bufs && vi->big_packets)
> +		return 0;
> +
> +	for (i = 0; i < vi->max_queue_pairs; i++) {
> +		struct receive_queue *rq = &vi->rq[i];
> +		struct page_pool_params pp_params = { 0 };
> +		struct device *dma_dev;
> +
> +		if (rq->page_pool)
> +			continue;
> +
> +		if (rq->xsk_pool)
> +			continue;
> +
> +		pp_params.order = 0;
> +		pp_params.pool_size = virtqueue_get_vring_size(rq->vq);
> +		pp_params.nid = dev_to_node(vi->vdev->dev.parent);
> +		pp_params.netdev = vi->dev;
> +		pp_params.napi = &rq->napi;
> +
> +		/* Check if backend supports DMA API (e.g., vhost, virtio-pci).
> +		 * If so, use page_pool's DMA mapping for premapped buffers.
> +		 * Otherwise (e.g., VDUSE), page_pool only handles allocation.
> +		 */
> +		dma_dev = virtqueue_dma_dev(rq->vq);
> +		if (dma_dev) {
> +			pp_params.dev = dma_dev;
> +			pp_params.flags = PP_FLAG_DMA_MAP;
> +			pp_params.dma_dir = DMA_FROM_DEVICE;
> +			rq->use_page_pool_dma = true;
> +		} else {
> +			pp_params.dev = vi->vdev->dev.parent;
> +			pp_params.flags = 0;
> +			rq->use_page_pool_dma = false;
> +		}
> +
> +		rq->page_pool = page_pool_create(&pp_params);
> +		if (IS_ERR(rq->page_pool)) {
> +			err = PTR_ERR(rq->page_pool);
> +			rq->page_pool = NULL;
> +			goto err_cleanup;
> +		}
> +	}
> +	return 0;
> +
> +err_cleanup:
> +	while (--i >= 0) {
> +		struct receive_queue *rq = &vi->rq[i];
> +
> +		if (rq->page_pool) {
> +			page_pool_destroy(rq->page_pool);
> +			rq->page_pool = NULL;
> +		}
> +	}
> +	return err;
> +}
> +
> +static void virtnet_destroy_page_pools(struct virtnet_info *vi)
> +{
> +	int i;
> +
> +	for (i = 0; i < vi->max_queue_pairs; i++) {
> +		struct receive_queue *rq = &vi->rq[i];
> +
> +		if (rq->page_pool) {
> +			page_pool_destroy(rq->page_pool);
> +			rq->page_pool = NULL;
> +		}
> +	}
> +}
> +
>  static int virtnet_open(struct net_device *dev)
>  {
>  	struct virtnet_info *vi = netdev_priv(dev);
> @@ -6441,10 +6479,8 @@ static int virtnet_find_vqs(struct virtnet_info *vi)
>  		vi->rq[i].min_buf_len = mergeable_min_buf_len(vi, vi->rq[i].vq);
>  		vi->sq[i].vq = vqs[txq2vq(i)];
>  	}
> -
>  	/* run here: ret == 0. */
>  
> -
>  err_find:
>  	kfree(ctx);
>  err_ctx:
> @@ -6945,6 +6981,14 @@ static int virtnet_probe(struct virtio_device *vdev)
>  			goto free;
>  	}
>  
> +	/* Create page pools for receive queues.
> +	 * Page pools are created at probe time so they can be used
> +	 * with premapped DMA addresses throughout the device lifetime.
> +	 */
> +	err = virtnet_create_page_pools(vi);
> +	if (err)
> +		goto free_irq_moder;
> +
>  #ifdef CONFIG_SYSFS
>  	if (vi->mergeable_rx_bufs)
>  		dev->sysfs_rx_queue_group = &virtio_net_mrg_rx_group;
> @@ -6958,7 +7002,7 @@ static int virtnet_probe(struct virtio_device *vdev)
>  		vi->failover = net_failover_create(vi->dev);
>  		if (IS_ERR(vi->failover)) {
>  			err = PTR_ERR(vi->failover);
> -			goto free_vqs;
> +			goto free_page_pools;
>  		}
>  	}
>  
> @@ -7075,7 +7119,10 @@ static int virtnet_probe(struct virtio_device *vdev)
>  	unregister_netdev(dev);
>  free_failover:
>  	net_failover_destroy(vi->failover);
> -free_vqs:
> +free_page_pools:
> +	virtnet_destroy_page_pools(vi);
> +free_irq_moder:
> +	virtnet_free_irq_moder(vi);
>  	virtio_reset_device(vdev);
>  	free_receive_page_frags(vi);
>  	virtnet_del_vqs(vi);
> @@ -7104,6 +7151,8 @@ static void remove_vq_common(struct virtnet_info *vi)
>  
>  	free_receive_page_frags(vi);
>  
> +	virtnet_destroy_page_pools(vi);
> +
>  	virtnet_del_vqs(vi);
>  }
>  
> -- 
> 2.47.3

Re: [PATCH net-next v4 1/2] virtio_net: add page_pool support for buffer allocation

Posted by Vishwanath Seshagiri 3 days, 14 hours ago


On 2/4/26 9:30 PM, Michael S. Tsirkin wrote:
> On Wed, Feb 04, 2026 at 11:36:16AM -0800, Vishwanath Seshagiri wrote:
>> Use page_pool for RX buffer allocation in mergeable and small buffer
>> modes to enable page recycling and avoid repeated page allocator calls.
>> skb_mark_for_recycle() enables page reuse in the network stack.
>>
>> Big packets mode is unchanged because it uses page->private for linked
>> list chaining of multiple pages per buffer, which conflicts with
>> page_pool's internal use of page->private.
>>
>> Implement conditional DMA premapping using virtqueue_dma_dev():
>> - When non-NULL (vhost, virtio-pci): use PP_FLAG_DMA_MAP with page_pool
>>    handling DMA mapping, submit via virtqueue_add_inbuf_premapped()
>> - When NULL (VDUSE, direct physical): page_pool handles allocation only,
>>    submit via virtqueue_add_inbuf_ctx()
>>
>> This preserves the DMA premapping optimization from commit 31f3cd4e5756b
>> ("virtio-net: rq submits premapped per-buffer") while adding page_pool
>> support as a prerequisite for future zero-copy features (devmem TCP,
>> io_uring ZCRX).
>>
>> Page pools are created in probe and destroyed in remove (not open/close),
>> following existing driver behavior where RX buffers remain in virtqueues
>> across interface state changes.
>>
>> Signed-off-by: Vishwanath Seshagiri <vishs@meta.com>
>> ---
>>   drivers/net/Kconfig      |   1 +
>>   drivers/net/virtio_net.c | 351 ++++++++++++++++++++++-----------------
>>   2 files changed, 201 insertions(+), 151 deletions(-)
>>
>> diff --git a/drivers/net/Kconfig b/drivers/net/Kconfig
>> index ac12eaf11755..f1e6b6b0a86f 100644
>> --- a/drivers/net/Kconfig
>> +++ b/drivers/net/Kconfig
>> @@ -450,6 +450,7 @@ config VIRTIO_NET
>>   	depends on VIRTIO
>>   	select NET_FAILOVER
>>   	select DIMLIB
>> +	select PAGE_POOL
>>   	help
>>   	  This is the virtual network driver for virtio.  It can be used with
>>   	  QEMU based VMMs (like KVM or Xen).  Say Y or M.
>> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
>> index db88dcaefb20..74c51e597c3f 100644
>> --- a/drivers/net/virtio_net.c
>> +++ b/drivers/net/virtio_net.c
>> @@ -26,6 +26,7 @@
>>   #include <net/netdev_rx_queue.h>
>>   #include <net/netdev_queues.h>
>>   #include <net/xdp_sock_drv.h>
>> +#include <net/page_pool/helpers.h>
>>   
>>   static int napi_weight = NAPI_POLL_WEIGHT;
>>   module_param(napi_weight, int, 0444);
>> @@ -359,6 +360,11 @@ struct receive_queue {
>>   	/* Page frag for packet buffer allocation. */
>>   	struct page_frag alloc_frag;
>>   
>> +	struct page_pool *page_pool;
>> +
>> +	/* True if page_pool handles DMA mapping via PP_FLAG_DMA_MAP */
>> +	bool use_page_pool_dma;
>> +
>>   	/* RX: fragments + linear part + virtio header */
>>   	struct scatterlist sg[MAX_SKB_FRAGS + 2];
>>   
>> @@ -521,11 +527,13 @@ static int virtnet_xdp_handler(struct bpf_prog *xdp_prog, struct xdp_buff *xdp,
>>   			       struct virtnet_rq_stats *stats);
>>   static void virtnet_receive_done(struct virtnet_info *vi, struct receive_queue *rq,
>>   				 struct sk_buff *skb, u8 flags);
>> -static struct sk_buff *virtnet_skb_append_frag(struct sk_buff *head_skb,
>> +static struct sk_buff *virtnet_skb_append_frag(struct receive_queue *rq,
>> +					       struct sk_buff *head_skb,
>>   					       struct sk_buff *curr_skb,
>>   					       struct page *page, void *buf,
>>   					       int len, int truesize);
>>   static void virtnet_xsk_completed(struct send_queue *sq, int num);
>> +static void free_unused_bufs(struct virtnet_info *vi);
>>   
>>   enum virtnet_xmit_type {
>>   	VIRTNET_XMIT_TYPE_SKB,
>> @@ -706,15 +714,24 @@ static struct page *get_a_page(struct receive_queue *rq, gfp_t gfp_mask)
>>   	return p;
>>   }
>>   
>> +static void virtnet_put_page(struct receive_queue *rq, struct page *page,
>> +			     bool allow_direct)
>> +{
>> +	if (page_pool_page_is_pp(page))
>> +		page_pool_put_page(rq->page_pool, page, -1, allow_direct);
>> +	else
>> +		put_page(page);
>> +}
>> +
>>   static void virtnet_rq_free_buf(struct virtnet_info *vi,
>>   				struct receive_queue *rq, void *buf)
>>   {
>>   	if (vi->mergeable_rx_bufs)
>> -		put_page(virt_to_head_page(buf));
>> +		virtnet_put_page(rq, virt_to_head_page(buf), false);
>>   	else if (vi->big_packets)
>>   		give_pages(rq, buf);
>>   	else
>> -		put_page(virt_to_head_page(buf));
>> +		virtnet_put_page(rq, virt_to_head_page(buf), false);
>>   }
>>   
>>   static void enable_rx_mode_work(struct virtnet_info *vi)
>> @@ -877,9 +894,12 @@ static struct sk_buff *page_to_skb(struct virtnet_info *vi,
>>   		if (unlikely(!skb))
>>   			return NULL;
>>   
>> -		page = (struct page *)page->private;
>> -		if (page)
>> -			give_pages(rq, page);
>> +		if (!rq->page_pool) {
> 
> I think this is ok because big_packets is exactly when this happens.
> but it is confusing that the conditions on free and alloc are
> written differently. A comment with an explanation, at least?

I will add a comment here in v5.

> 
> 
>> +			page = (struct page *)page->private;
>> +			if (page)
>> +				give_pages(rq, page);
>> +		}
>> +
>>   		goto ok;
>>   	}
>>   
>> @@ -925,7 +945,7 @@ static struct sk_buff *page_to_skb(struct virtnet_info *vi,
>>   	hdr = skb_vnet_common_hdr(skb);
>>   	memcpy(hdr, hdr_p, hdr_len);
>>   	if (page_to_free)
>> -		put_page(page_to_free);
>> +		virtnet_put_page(rq, page_to_free, true);
>>   
>>   	return skb;
>>   }
>> @@ -965,93 +985,10 @@ static void virtnet_rq_unmap(struct receive_queue *rq, void *buf, u32 len)
>>   static void *virtnet_rq_get_buf(struct receive_queue *rq, u32 *len, void **ctx)
>>   {
>>   	struct virtnet_info *vi = rq->vq->vdev->priv;
>> -	void *buf;
>> -
>> -	BUG_ON(vi->big_packets && !vi->mergeable_rx_bufs);
>> -
>> -	buf = virtqueue_get_buf_ctx(rq->vq, len, ctx);
>> -	if (buf)
>> -		virtnet_rq_unmap(rq, buf, *len);
>> -
>> -	return buf;
>> -}
>> -
>> -static void virtnet_rq_init_one_sg(struct receive_queue *rq, void *buf, u32 len)
>> -{
>> -	struct virtnet_info *vi = rq->vq->vdev->priv;
>> -	struct virtnet_rq_dma *dma;
>> -	dma_addr_t addr;
>> -	u32 offset;
>> -	void *head;
>> -
>> -	BUG_ON(vi->big_packets && !vi->mergeable_rx_bufs);
>> -
>> -	head = page_address(rq->alloc_frag.page);
>> -
>> -	offset = buf - head;
>> -
>> -	dma = head;
>> -
>> -	addr = dma->addr - sizeof(*dma) + offset;
>> -
>> -	sg_init_table(rq->sg, 1);
>> -	sg_fill_dma(rq->sg, addr, len);
>> -}
>> -
>> -static void *virtnet_rq_alloc(struct receive_queue *rq, u32 size, gfp_t gfp)
>> -{
>> -	struct page_frag *alloc_frag = &rq->alloc_frag;
>> -	struct virtnet_info *vi = rq->vq->vdev->priv;
>> -	struct virtnet_rq_dma *dma;
>> -	void *buf, *head;
>> -	dma_addr_t addr;
>>   
>>   	BUG_ON(vi->big_packets && !vi->mergeable_rx_bufs);
>>   
>> -	head = page_address(alloc_frag->page);
>> -
>> -	dma = head;
>> -
>> -	/* new pages */
>> -	if (!alloc_frag->offset) {
>> -		if (rq->last_dma) {
>> -			/* Now, the new page is allocated, the last dma
>> -			 * will not be used. So the dma can be unmapped
>> -			 * if the ref is 0.
>> -			 */
>> -			virtnet_rq_unmap(rq, rq->last_dma, 0);
>> -			rq->last_dma = NULL;
>> -		}
>> -
>> -		dma->len = alloc_frag->size - sizeof(*dma);
>> -
>> -		addr = virtqueue_map_single_attrs(rq->vq, dma + 1,
>> -						  dma->len, DMA_FROM_DEVICE, 0);
>> -		if (virtqueue_map_mapping_error(rq->vq, addr))
>> -			return NULL;
>> -
>> -		dma->addr = addr;
>> -		dma->need_sync = virtqueue_map_need_sync(rq->vq, addr);
> 
> it gives me pause that this patch never does sync.
> don't you need page_pool_dma_sync_for_cpu somewhere?

I missed the page_pool_dma_sync_for_cpu in the receive path before
reading the buffer data. I will add it in v5.

> 
> 
> 
>> -
>> -		/* Add a reference to dma to prevent the entire dma from
>> -		 * being released during error handling. This reference
>> -		 * will be freed after the pages are no longer used.
>> -		 */
>> -		get_page(alloc_frag->page);
>> -		dma->ref = 1;
>> -		alloc_frag->offset = sizeof(*dma);
>> -
>> -		rq->last_dma = dma;
>> -	}
>> -
>> -	++dma->ref;
>> -
>> -	buf = head + alloc_frag->offset;
>> -
>> -	get_page(alloc_frag->page);
>> -	alloc_frag->offset += size;
>> -
>> -	return buf;
>> +	return virtqueue_get_buf_ctx(rq->vq, len, ctx);
>>   }
>>   
>>   static void virtnet_rq_unmap_free_buf(struct virtqueue *vq, void *buf)
>> @@ -1067,9 +1004,6 @@ static void virtnet_rq_unmap_free_buf(struct virtqueue *vq, void *buf)
>>   		return;
>>   	}
>>   
>> -	if (!vi->big_packets || vi->mergeable_rx_bufs)
>> -		virtnet_rq_unmap(rq, buf, 0);
>> -
>>   	virtnet_rq_free_buf(vi, rq, buf);
>>   }
>>   
>> @@ -1335,7 +1269,7 @@ static int xsk_append_merge_buffer(struct virtnet_info *vi,
>>   
>>   		truesize = len;
>>   
>> -		curr_skb  = virtnet_skb_append_frag(head_skb, curr_skb, page,
>> +		curr_skb  = virtnet_skb_append_frag(rq, head_skb, curr_skb, page,
>>   						    buf, len, truesize);
>>   		if (!curr_skb) {
>>   			put_page(page);
>> @@ -1771,7 +1705,7 @@ static int virtnet_xdp_xmit(struct net_device *dev,
>>   	return ret;
>>   }
>>   
>> -static void put_xdp_frags(struct xdp_buff *xdp)
>> +static void put_xdp_frags(struct receive_queue *rq, struct xdp_buff *xdp)
>>   {
>>   	struct skb_shared_info *shinfo;
>>   	struct page *xdp_page;
>> @@ -1781,7 +1715,7 @@ static void put_xdp_frags(struct xdp_buff *xdp)
>>   		shinfo = xdp_get_shared_info_from_buff(xdp);
>>   		for (i = 0; i < shinfo->nr_frags; i++) {
>>   			xdp_page = skb_frag_page(&shinfo->frags[i]);
>> -			put_page(xdp_page);
>> +			virtnet_put_page(rq, xdp_page, true);
>>   		}
>>   	}
>>   }
>> @@ -1873,7 +1807,7 @@ static struct page *xdp_linearize_page(struct net_device *dev,
>>   	if (page_off + *len + tailroom > PAGE_SIZE)
>>   		return NULL;
>>   
>> -	page = alloc_page(GFP_ATOMIC);
>> +	page = page_pool_alloc_pages(rq->page_pool, GFP_ATOMIC);
>>   	if (!page)
>>   		return NULL;
>>   
>> @@ -1897,7 +1831,7 @@ static struct page *xdp_linearize_page(struct net_device *dev,
>>   		off = buf - page_address(p);
>>   
>>   		if (check_mergeable_len(dev, ctx, buflen)) {
>> -			put_page(p);
>> +			virtnet_put_page(rq, p, true);
>>   			goto err_buf;
>>   		}
>>   
>> @@ -1905,21 +1839,21 @@ static struct page *xdp_linearize_page(struct net_device *dev,
>>   		 * is sending packet larger than the MTU.
>>   		 */
>>   		if ((page_off + buflen + tailroom) > PAGE_SIZE) {
>> -			put_page(p);
>> +			virtnet_put_page(rq, p, true);
>>   			goto err_buf;
>>   		}
>>   
>>   		memcpy(page_address(page) + page_off,
>>   		       page_address(p) + off, buflen);
>>   		page_off += buflen;
>> -		put_page(p);
>> +		virtnet_put_page(rq, p, true);
>>   	}
>>   
>>   	/* Headroom does not contribute to packet length */
>>   	*len = page_off - XDP_PACKET_HEADROOM;
>>   	return page;
>>   err_buf:
>> -	__free_pages(page, 0);
>> +	page_pool_put_page(rq->page_pool, page, -1, true);
>>   	return NULL;
>>   }
>>   
>> @@ -1996,7 +1930,7 @@ static struct sk_buff *receive_small_xdp(struct net_device *dev,
>>   			goto err_xdp;
>>   
>>   		buf = page_address(xdp_page);
>> -		put_page(page);
>> +		virtnet_put_page(rq, page, true);
>>   		page = xdp_page;
>>   	}
>>   
>> @@ -2028,13 +1962,15 @@ static struct sk_buff *receive_small_xdp(struct net_device *dev,
>>   	if (metasize)
>>   		skb_metadata_set(skb, metasize);
>>   
>> +	skb_mark_for_recycle(skb);
>> +
>>   	return skb;
>>   
>>   err_xdp:
>>   	u64_stats_inc(&stats->xdp_drops);
>>   err:
>>   	u64_stats_inc(&stats->drops);
>> -	put_page(page);
>> +	virtnet_put_page(rq, page, true);
>>   xdp_xmit:
>>   	return NULL;
>>   }
>> @@ -2082,12 +2018,14 @@ static struct sk_buff *receive_small(struct net_device *dev,
>>   	}
>>   
>>   	skb = receive_small_build_skb(vi, xdp_headroom, buf, len);
>> -	if (likely(skb))
>> +	if (likely(skb)) {
>> +		skb_mark_for_recycle(skb);
>>   		return skb;
>> +	}
>>   
>>   err:
>>   	u64_stats_inc(&stats->drops);
>> -	put_page(page);
>> +	virtnet_put_page(rq, page, true);
>>   	return NULL;
>>   }
>>   
>> @@ -2142,7 +2080,7 @@ static void mergeable_buf_free(struct receive_queue *rq, int num_buf,
>>   		}
>>   		u64_stats_add(&stats->bytes, len);
>>   		page = virt_to_head_page(buf);
>> -		put_page(page);
>> +		virtnet_put_page(rq, page, true);
>>   	}
>>   }
>>   
>> @@ -2253,7 +2191,7 @@ static int virtnet_build_xdp_buff_mrg(struct net_device *dev,
>>   		offset = buf - page_address(page);
>>   
>>   		if (check_mergeable_len(dev, ctx, len)) {
>> -			put_page(page);
>> +			virtnet_put_page(rq, page, true);
>>   			goto err;
>>   		}
>>   
>> @@ -2272,7 +2210,7 @@ static int virtnet_build_xdp_buff_mrg(struct net_device *dev,
>>   	return 0;
>>   
>>   err:
>> -	put_xdp_frags(xdp);
>> +	put_xdp_frags(rq, xdp);
>>   	return -EINVAL;
>>   }
>>   
>> @@ -2337,7 +2275,7 @@ static void *mergeable_xdp_get_buf(struct virtnet_info *vi,
>>   		if (*len + xdp_room > PAGE_SIZE)
>>   			return NULL;
>>   
>> -		xdp_page = alloc_page(GFP_ATOMIC);
>> +		xdp_page = page_pool_alloc_pages(rq->page_pool, GFP_ATOMIC);
>>   		if (!xdp_page)
>>   			return NULL;
>>   
>> @@ -2347,7 +2285,7 @@ static void *mergeable_xdp_get_buf(struct virtnet_info *vi,
>>   
>>   	*frame_sz = PAGE_SIZE;
>>   
>> -	put_page(*page);
>> +	virtnet_put_page(rq, *page, true);
>>   
>>   	*page = xdp_page;
>>   
>> @@ -2393,6 +2331,8 @@ static struct sk_buff *receive_mergeable_xdp(struct net_device *dev,
>>   		head_skb = build_skb_from_xdp_buff(dev, vi, &xdp, xdp_frags_truesz);
>>   		if (unlikely(!head_skb))
>>   			break;
>> +
>> +		skb_mark_for_recycle(head_skb);
>>   		return head_skb;
>>   
>>   	case XDP_TX:
>> @@ -2403,10 +2343,10 @@ static struct sk_buff *receive_mergeable_xdp(struct net_device *dev,
>>   		break;
>>   	}
>>   
>> -	put_xdp_frags(&xdp);
>> +	put_xdp_frags(rq, &xdp);
>>   
>>   err_xdp:
>> -	put_page(page);
>> +	virtnet_put_page(rq, page, true);
>>   	mergeable_buf_free(rq, num_buf, dev, stats);
>>   
>>   	u64_stats_inc(&stats->xdp_drops);
>> @@ -2414,7 +2354,8 @@ static struct sk_buff *receive_mergeable_xdp(struct net_device *dev,
>>   	return NULL;
>>   }
>>   
>> -static struct sk_buff *virtnet_skb_append_frag(struct sk_buff *head_skb,
>> +static struct sk_buff *virtnet_skb_append_frag(struct receive_queue *rq,
>> +					       struct sk_buff *head_skb,
>>   					       struct sk_buff *curr_skb,
>>   					       struct page *page, void *buf,
>>   					       int len, int truesize)
>> @@ -2446,7 +2387,7 @@ static struct sk_buff *virtnet_skb_append_frag(struct sk_buff *head_skb,
>>   
>>   	offset = buf - page_address(page);
>>   	if (skb_can_coalesce(curr_skb, num_skb_frags, page, offset)) {
>> -		put_page(page);
>> +		virtnet_put_page(rq, page, true);
>>   		skb_coalesce_rx_frag(curr_skb, num_skb_frags - 1,
>>   				     len, truesize);
>>   	} else {
>> @@ -2499,6 +2440,8 @@ static struct sk_buff *receive_mergeable(struct net_device *dev,
>>   
>>   	if (unlikely(!curr_skb))
>>   		goto err_skb;
>> +
>> +	skb_mark_for_recycle(head_skb);
>>   	while (--num_buf) {
>>   		buf = virtnet_rq_get_buf(rq, &len, &ctx);
>>   		if (unlikely(!buf)) {
>> @@ -2517,7 +2460,7 @@ static struct sk_buff *receive_mergeable(struct net_device *dev,
>>   			goto err_skb;
>>   
>>   		truesize = mergeable_ctx_to_truesize(ctx);
>> -		curr_skb  = virtnet_skb_append_frag(head_skb, curr_skb, page,
>> +		curr_skb  = virtnet_skb_append_frag(rq, head_skb, curr_skb, page,
>>   						    buf, len, truesize);
>>   		if (!curr_skb)
>>   			goto err_skb;
>> @@ -2527,7 +2470,7 @@ static struct sk_buff *receive_mergeable(struct net_device *dev,
>>   	return head_skb;
>>   
>>   err_skb:
>> -	put_page(page);
>> +	virtnet_put_page(rq, page, true);
>>   	mergeable_buf_free(rq, num_buf, dev, stats);
>>   
>>   err_buf:
>> @@ -2666,32 +2609,42 @@ static void receive_buf(struct virtnet_info *vi, struct receive_queue *rq,
>>   static int add_recvbuf_small(struct virtnet_info *vi, struct receive_queue *rq,
>>   			     gfp_t gfp)
>>   {
>> -	char *buf;
>>   	unsigned int xdp_headroom = virtnet_get_headroom(vi);
>>   	void *ctx = (void *)(unsigned long)xdp_headroom;
>>   	int len = vi->hdr_len + VIRTNET_RX_PAD + GOOD_PACKET_LEN + xdp_headroom;
>> +	unsigned int offset;
>> +	struct page *page;
>> +	dma_addr_t addr;
>> +	char *buf;
>>   	int err;
>>   
>>   	len = SKB_DATA_ALIGN(len) +
>>   	      SKB_DATA_ALIGN(sizeof(struct skb_shared_info));
>>   
>> -	if (unlikely(!skb_page_frag_refill(len, &rq->alloc_frag, gfp)))
>> -		return -ENOMEM;
>> -
>> -	buf = virtnet_rq_alloc(rq, len, gfp);
>> -	if (unlikely(!buf))
>> +	page = page_pool_alloc_frag(rq->page_pool, &offset, len, gfp);
>> +	if (unlikely(!page))
>>   		return -ENOMEM;
>>   
>> +	buf = page_address(page) + offset;
>>   	buf += VIRTNET_RX_PAD + xdp_headroom;
>>   
>> -	virtnet_rq_init_one_sg(rq, buf, vi->hdr_len + GOOD_PACKET_LEN);
>> +	if (rq->use_page_pool_dma) {
>> +		addr = page_pool_get_dma_addr(page) + offset;
>> +		addr += VIRTNET_RX_PAD + xdp_headroom;
>>   
>> -	err = virtqueue_add_inbuf_premapped(rq->vq, rq->sg, 1, buf, ctx, gfp);
>> -	if (err < 0) {
>> -		virtnet_rq_unmap(rq, buf, 0);
>> -		put_page(virt_to_head_page(buf));
>> +		sg_init_table(rq->sg, 1);
>> +		sg_fill_dma(rq->sg, addr, vi->hdr_len + GOOD_PACKET_LEN);
>> +		err = virtqueue_add_inbuf_premapped(rq->vq, rq->sg, 1,
>> +						    buf, ctx, gfp);
>> +	} else {
>> +		sg_init_one(rq->sg, buf, vi->hdr_len + GOOD_PACKET_LEN);
>> +		err = virtqueue_add_inbuf_ctx(rq->vq, rq->sg, 1,
>> +					      buf, ctx, gfp);
>>   	}
>>   
>> +	if (err < 0)
>> +		page_pool_put_page(rq->page_pool, virt_to_head_page(buf),
>> +				   -1, false);
>>   	return err;
>>   }
>>   
>> @@ -2764,13 +2717,15 @@ static unsigned int get_mergeable_buf_len(struct receive_queue *rq,
>>   static int add_recvbuf_mergeable(struct virtnet_info *vi,
>>   				 struct receive_queue *rq, gfp_t gfp)
>>   {
>> -	struct page_frag *alloc_frag = &rq->alloc_frag;
>>   	unsigned int headroom = virtnet_get_headroom(vi);
>>   	unsigned int tailroom = headroom ? sizeof(struct skb_shared_info) : 0;
>>   	unsigned int room = SKB_DATA_ALIGN(headroom + tailroom);
>>   	unsigned int len, hole;
>> -	void *ctx;
>> +	unsigned int offset;
>> +	struct page *page;
>> +	dma_addr_t addr;
>>   	char *buf;
>> +	void *ctx;
>>   	int err;
>>   
>>   	/* Extra tailroom is needed to satisfy XDP's assumption. This
>> @@ -2779,18 +2734,14 @@ static int add_recvbuf_mergeable(struct virtnet_info *vi,
>>   	 */
>>   	len = get_mergeable_buf_len(rq, &rq->mrg_avg_pkt_len, room);
>>   
>> -	if (unlikely(!skb_page_frag_refill(len + room, alloc_frag, gfp)))
>> -		return -ENOMEM;
>> -
>> -	if (!alloc_frag->offset && len + room + sizeof(struct virtnet_rq_dma) > alloc_frag->size)
>> -		len -= sizeof(struct virtnet_rq_dma);
>> -
>> -	buf = virtnet_rq_alloc(rq, len + room, gfp);
>> -	if (unlikely(!buf))
>> +	page = page_pool_alloc_frag(rq->page_pool, &offset, len + room, gfp);
>> +	if (unlikely(!page))
>>   		return -ENOMEM;
>>   
>> +	buf = page_address(page) + offset;
>>   	buf += headroom; /* advance address leaving hole at front of pkt */
>> -	hole = alloc_frag->size - alloc_frag->offset;
>> +
>> +	hole = PAGE_SIZE - (offset + len + room);
>>   	if (hole < len + room) {
>>   		/* To avoid internal fragmentation, if there is very likely not
>>   		 * enough space for another buffer, add the remaining space to
>> @@ -2800,18 +2751,27 @@ static int add_recvbuf_mergeable(struct virtnet_info *vi,
>>   		 */
>>   		if (!headroom)
>>   			len += hole;
>> -		alloc_frag->offset += hole;
> 
> Hmm. All these allocations are tricky.
> So we used to advance offset by hole but with page pool api
> what advances pool->frag_offset? If nothing will not the next
> small allocation reuse the space and overlap the buffer?

I tested with debug tracing and confirmed the issue triggers with
typical 1536-byte allocations. When len += hole extends the buffer into
3072-4096, page_pool's internal frag_offset stays at 3072, so a
subsequent smaller allocation could overlap.
Since page_pool manages frag_offset internally and there's no API to
advance it past the hole, the fix is to remove the if (hole < len +
room) block entirely.

> 
> 
>>   	}
>>   
>> -	virtnet_rq_init_one_sg(rq, buf, len);
>> -
>>   	ctx = mergeable_len_to_ctx(len + room, headroom);
>> -	err = virtqueue_add_inbuf_premapped(rq->vq, rq->sg, 1, buf, ctx, gfp);
>> -	if (err < 0) {
>> -		virtnet_rq_unmap(rq, buf, 0);
>> -		put_page(virt_to_head_page(buf));
>> +
>> +	if (rq->use_page_pool_dma) {
>> +		addr = page_pool_get_dma_addr(page) + offset;
>> +		addr += headroom;
>> +
>> +		sg_init_table(rq->sg, 1);
>> +		sg_fill_dma(rq->sg, addr, len);
>> +		err = virtqueue_add_inbuf_premapped(rq->vq, rq->sg, 1,
>> +						    buf, ctx, gfp);
>> +	} else {
>> +		sg_init_one(rq->sg, buf, len);
>> +		err = virtqueue_add_inbuf_ctx(rq->vq, rq->sg, 1,
>> +					      buf, ctx, gfp);
>>   	}
>>   
>> +	if (err < 0)
>> +		page_pool_put_page(rq->page_pool, virt_to_head_page(buf),
>> +				   -1, false);
>>   	return err;
>>   }
>>   
>> @@ -3128,7 +3088,10 @@ static int virtnet_enable_queue_pair(struct virtnet_info *vi, int qp_index)
>>   		return err;
>>   
>>   	err = xdp_rxq_info_reg_mem_model(&vi->rq[qp_index].xdp_rxq,
>> -					 MEM_TYPE_PAGE_SHARED, NULL);
>> +					 vi->rq[qp_index].page_pool ?
>> +						MEM_TYPE_PAGE_POOL :
>> +						MEM_TYPE_PAGE_SHARED,
>> +					 vi->rq[qp_index].page_pool);
>>   	if (err < 0)
>>   		goto err_xdp_reg_mem_model;
>>   
>> @@ -3168,6 +3131,81 @@ static void virtnet_update_settings(struct virtnet_info *vi)
>>   		vi->duplex = duplex;
>>   }
>>   
>> +static int virtnet_create_page_pools(struct virtnet_info *vi)
>> +{
>> +	int i, err;
>> +
>> +	if (!vi->mergeable_rx_bufs && vi->big_packets)
>> +		return 0;
>> +
>> +	for (i = 0; i < vi->max_queue_pairs; i++) {
>> +		struct receive_queue *rq = &vi->rq[i];
>> +		struct page_pool_params pp_params = { 0 };
>> +		struct device *dma_dev;
>> +
>> +		if (rq->page_pool)
>> +			continue;
>> +
>> +		if (rq->xsk_pool)
>> +			continue;
>> +
>> +		pp_params.order = 0;
>> +		pp_params.pool_size = virtqueue_get_vring_size(rq->vq);
>> +		pp_params.nid = dev_to_node(vi->vdev->dev.parent);
>> +		pp_params.netdev = vi->dev;
>> +		pp_params.napi = &rq->napi;
>> +
>> +		/* Check if backend supports DMA API (e.g., vhost, virtio-pci).
>> +		 * If so, use page_pool's DMA mapping for premapped buffers.
>> +		 * Otherwise (e.g., VDUSE), page_pool only handles allocation.
>> +		 */
>> +		dma_dev = virtqueue_dma_dev(rq->vq);
>> +		if (dma_dev) {
>> +			pp_params.dev = dma_dev;
>> +			pp_params.flags = PP_FLAG_DMA_MAP;
>> +			pp_params.dma_dir = DMA_FROM_DEVICE;
>> +			rq->use_page_pool_dma = true;
>> +		} else {
>> +			pp_params.dev = vi->vdev->dev.parent;
>> +			pp_params.flags = 0;
>> +			rq->use_page_pool_dma = false;
>> +		}
>> +
>> +		rq->page_pool = page_pool_create(&pp_params);
>> +		if (IS_ERR(rq->page_pool)) {
>> +			err = PTR_ERR(rq->page_pool);
>> +			rq->page_pool = NULL;
>> +			goto err_cleanup;
>> +		}
>> +	}
>> +	return 0;
>> +
>> +err_cleanup:
>> +	while (--i >= 0) {
>> +		struct receive_queue *rq = &vi->rq[i];
>> +
>> +		if (rq->page_pool) {
>> +			page_pool_destroy(rq->page_pool);
>> +			rq->page_pool = NULL;
>> +		}
>> +	}
>> +	return err;
>> +}
>> +
>> +static void virtnet_destroy_page_pools(struct virtnet_info *vi)
>> +{
>> +	int i;
>> +
>> +	for (i = 0; i < vi->max_queue_pairs; i++) {
>> +		struct receive_queue *rq = &vi->rq[i];
>> +
>> +		if (rq->page_pool) {
>> +			page_pool_destroy(rq->page_pool);
>> +			rq->page_pool = NULL;
>> +		}
>> +	}
>> +}
>> +
>>   static int virtnet_open(struct net_device *dev)
>>   {
>>   	struct virtnet_info *vi = netdev_priv(dev);
>> @@ -6441,10 +6479,8 @@ static int virtnet_find_vqs(struct virtnet_info *vi)
>>   		vi->rq[i].min_buf_len = mergeable_min_buf_len(vi, vi->rq[i].vq);
>>   		vi->sq[i].vq = vqs[txq2vq(i)];
>>   	}
>> -
>>   	/* run here: ret == 0. */
>>   
>> -
>>   err_find:
>>   	kfree(ctx);
>>   err_ctx:
>> @@ -6945,6 +6981,14 @@ static int virtnet_probe(struct virtio_device *vdev)
>>   			goto free;
>>   	}
>>   
>> +	/* Create page pools for receive queues.
>> +	 * Page pools are created at probe time so they can be used
>> +	 * with premapped DMA addresses throughout the device lifetime.
>> +	 */
>> +	err = virtnet_create_page_pools(vi);
>> +	if (err)
>> +		goto free_irq_moder;
>> +
>>   #ifdef CONFIG_SYSFS
>>   	if (vi->mergeable_rx_bufs)
>>   		dev->sysfs_rx_queue_group = &virtio_net_mrg_rx_group;
>> @@ -6958,7 +7002,7 @@ static int virtnet_probe(struct virtio_device *vdev)
>>   		vi->failover = net_failover_create(vi->dev);
>>   		if (IS_ERR(vi->failover)) {
>>   			err = PTR_ERR(vi->failover);
>> -			goto free_vqs;
>> +			goto free_page_pools;
>>   		}
>>   	}
>>   
>> @@ -7075,7 +7119,10 @@ static int virtnet_probe(struct virtio_device *vdev)
>>   	unregister_netdev(dev);
>>   free_failover:
>>   	net_failover_destroy(vi->failover);
>> -free_vqs:
>> +free_page_pools:
>> +	virtnet_destroy_page_pools(vi);
>> +free_irq_moder:
>> +	virtnet_free_irq_moder(vi);
>>   	virtio_reset_device(vdev);
>>   	free_receive_page_frags(vi);
>>   	virtnet_del_vqs(vi);
>> @@ -7104,6 +7151,8 @@ static void remove_vq_common(struct virtnet_info *vi)
>>   
>>   	free_receive_page_frags(vi);
>>   
>> +	virtnet_destroy_page_pools(vi);
>> +
>>   	virtnet_del_vqs(vi);
>>   }
>>   
>> -- 
>> 2.47.3
>

Re: [PATCH net-next v4 1/2] virtio_net: add page_pool support for buffer allocation

Posted by Michael S. Tsirkin 3 days, 14 hours ago

On Wed, Feb 04, 2026 at 10:34:38PM -0800, Vishwanath Seshagiri wrote:
> 
> 
> On 2/4/26 9:30 PM, Michael S. Tsirkin wrote:
> > On Wed, Feb 04, 2026 at 11:36:16AM -0800, Vishwanath Seshagiri wrote:
> > > Use page_pool for RX buffer allocation in mergeable and small buffer
> > > modes to enable page recycling and avoid repeated page allocator calls.
> > > skb_mark_for_recycle() enables page reuse in the network stack.
> > > 
> > > Big packets mode is unchanged because it uses page->private for linked
> > > list chaining of multiple pages per buffer, which conflicts with
> > > page_pool's internal use of page->private.
> > > 
> > > Implement conditional DMA premapping using virtqueue_dma_dev():
> > > - When non-NULL (vhost, virtio-pci): use PP_FLAG_DMA_MAP with page_pool
> > >    handling DMA mapping, submit via virtqueue_add_inbuf_premapped()
> > > - When NULL (VDUSE, direct physical): page_pool handles allocation only,
> > >    submit via virtqueue_add_inbuf_ctx()
> > > 
> > > This preserves the DMA premapping optimization from commit 31f3cd4e5756b
> > > ("virtio-net: rq submits premapped per-buffer") while adding page_pool
> > > support as a prerequisite for future zero-copy features (devmem TCP,
> > > io_uring ZCRX).
> > > 
> > > Page pools are created in probe and destroyed in remove (not open/close),
> > > following existing driver behavior where RX buffers remain in virtqueues
> > > across interface state changes.
> > > 
> > > Signed-off-by: Vishwanath Seshagiri <vishs@meta.com>
> > > ---
> > >   drivers/net/Kconfig      |   1 +
> > >   drivers/net/virtio_net.c | 351 ++++++++++++++++++++++-----------------
> > >   2 files changed, 201 insertions(+), 151 deletions(-)
> > > 
> > > diff --git a/drivers/net/Kconfig b/drivers/net/Kconfig
> > > index ac12eaf11755..f1e6b6b0a86f 100644
> > > --- a/drivers/net/Kconfig
> > > +++ b/drivers/net/Kconfig
> > > @@ -450,6 +450,7 @@ config VIRTIO_NET
> > >   	depends on VIRTIO
> > >   	select NET_FAILOVER
> > >   	select DIMLIB
> > > +	select PAGE_POOL
> > >   	help
> > >   	  This is the virtual network driver for virtio.  It can be used with
> > >   	  QEMU based VMMs (like KVM or Xen).  Say Y or M.
> > > diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> > > index db88dcaefb20..74c51e597c3f 100644
> > > --- a/drivers/net/virtio_net.c
> > > +++ b/drivers/net/virtio_net.c
> > > @@ -26,6 +26,7 @@
> > >   #include <net/netdev_rx_queue.h>
> > >   #include <net/netdev_queues.h>
> > >   #include <net/xdp_sock_drv.h>
> > > +#include <net/page_pool/helpers.h>
> > >   static int napi_weight = NAPI_POLL_WEIGHT;
> > >   module_param(napi_weight, int, 0444);
> > > @@ -359,6 +360,11 @@ struct receive_queue {
> > >   	/* Page frag for packet buffer allocation. */
> > >   	struct page_frag alloc_frag;
> > > +	struct page_pool *page_pool;
> > > +
> > > +	/* True if page_pool handles DMA mapping via PP_FLAG_DMA_MAP */
> > > +	bool use_page_pool_dma;
> > > +
> > >   	/* RX: fragments + linear part + virtio header */
> > >   	struct scatterlist sg[MAX_SKB_FRAGS + 2];
> > > @@ -521,11 +527,13 @@ static int virtnet_xdp_handler(struct bpf_prog *xdp_prog, struct xdp_buff *xdp,
> > >   			       struct virtnet_rq_stats *stats);
> > >   static void virtnet_receive_done(struct virtnet_info *vi, struct receive_queue *rq,
> > >   				 struct sk_buff *skb, u8 flags);
> > > -static struct sk_buff *virtnet_skb_append_frag(struct sk_buff *head_skb,
> > > +static struct sk_buff *virtnet_skb_append_frag(struct receive_queue *rq,
> > > +					       struct sk_buff *head_skb,
> > >   					       struct sk_buff *curr_skb,
> > >   					       struct page *page, void *buf,
> > >   					       int len, int truesize);
> > >   static void virtnet_xsk_completed(struct send_queue *sq, int num);
> > > +static void free_unused_bufs(struct virtnet_info *vi);
> > >   enum virtnet_xmit_type {
> > >   	VIRTNET_XMIT_TYPE_SKB,
> > > @@ -706,15 +714,24 @@ static struct page *get_a_page(struct receive_queue *rq, gfp_t gfp_mask)
> > >   	return p;
> > >   }
> > > +static void virtnet_put_page(struct receive_queue *rq, struct page *page,
> > > +			     bool allow_direct)
> > > +{
> > > +	if (page_pool_page_is_pp(page))
> > > +		page_pool_put_page(rq->page_pool, page, -1, allow_direct);
> > > +	else
> > > +		put_page(page);
> > > +}
> > > +
> > >   static void virtnet_rq_free_buf(struct virtnet_info *vi,
> > >   				struct receive_queue *rq, void *buf)
> > >   {
> > >   	if (vi->mergeable_rx_bufs)
> > > -		put_page(virt_to_head_page(buf));
> > > +		virtnet_put_page(rq, virt_to_head_page(buf), false);
> > >   	else if (vi->big_packets)
> > >   		give_pages(rq, buf);
> > >   	else
> > > -		put_page(virt_to_head_page(buf));
> > > +		virtnet_put_page(rq, virt_to_head_page(buf), false);
> > >   }
> > >   static void enable_rx_mode_work(struct virtnet_info *vi)
> > > @@ -877,9 +894,12 @@ static struct sk_buff *page_to_skb(struct virtnet_info *vi,
> > >   		if (unlikely(!skb))
> > >   			return NULL;
> > > -		page = (struct page *)page->private;
> > > -		if (page)
> > > -			give_pages(rq, page);
> > > +		if (!rq->page_pool) {
> > 
> > I think this is ok because big_packets is exactly when this happens.
> > but it is confusing that the conditions on free and alloc are
> > written differently. A comment with an explanation, at least?
> 
> I will add a comment here in v5.

Would be better to also unify the way we test on alloc and free paths,
if possible.


> > 
> > 
> > > +			page = (struct page *)page->private;
> > > +			if (page)
> > > +				give_pages(rq, page);
> > > +		}
> > > +
> > >   		goto ok;
> > >   	}
> > > @@ -925,7 +945,7 @@ static struct sk_buff *page_to_skb(struct virtnet_info *vi,
> > >   	hdr = skb_vnet_common_hdr(skb);
> > >   	memcpy(hdr, hdr_p, hdr_len);
> > >   	if (page_to_free)
> > > -		put_page(page_to_free);
> > > +		virtnet_put_page(rq, page_to_free, true);
> > >   	return skb;
> > >   }
> > > @@ -965,93 +985,10 @@ static void virtnet_rq_unmap(struct receive_queue *rq, void *buf, u32 len)
> > >   static void *virtnet_rq_get_buf(struct receive_queue *rq, u32 *len, void **ctx)
> > >   {
> > >   	struct virtnet_info *vi = rq->vq->vdev->priv;
> > > -	void *buf;
> > > -
> > > -	BUG_ON(vi->big_packets && !vi->mergeable_rx_bufs);
> > > -
> > > -	buf = virtqueue_get_buf_ctx(rq->vq, len, ctx);
> > > -	if (buf)
> > > -		virtnet_rq_unmap(rq, buf, *len);
> > > -
> > > -	return buf;
> > > -}
> > > -
> > > -static void virtnet_rq_init_one_sg(struct receive_queue *rq, void *buf, u32 len)
> > > -{
> > > -	struct virtnet_info *vi = rq->vq->vdev->priv;
> > > -	struct virtnet_rq_dma *dma;
> > > -	dma_addr_t addr;
> > > -	u32 offset;
> > > -	void *head;
> > > -
> > > -	BUG_ON(vi->big_packets && !vi->mergeable_rx_bufs);
> > > -
> > > -	head = page_address(rq->alloc_frag.page);
> > > -
> > > -	offset = buf - head;
> > > -
> > > -	dma = head;
> > > -
> > > -	addr = dma->addr - sizeof(*dma) + offset;
> > > -
> > > -	sg_init_table(rq->sg, 1);
> > > -	sg_fill_dma(rq->sg, addr, len);
> > > -}
> > > -
> > > -static void *virtnet_rq_alloc(struct receive_queue *rq, u32 size, gfp_t gfp)
> > > -{
> > > -	struct page_frag *alloc_frag = &rq->alloc_frag;
> > > -	struct virtnet_info *vi = rq->vq->vdev->priv;
> > > -	struct virtnet_rq_dma *dma;
> > > -	void *buf, *head;
> > > -	dma_addr_t addr;
> > >   	BUG_ON(vi->big_packets && !vi->mergeable_rx_bufs);
> > > -	head = page_address(alloc_frag->page);
> > > -
> > > -	dma = head;
> > > -
> > > -	/* new pages */
> > > -	if (!alloc_frag->offset) {
> > > -		if (rq->last_dma) {
> > > -			/* Now, the new page is allocated, the last dma
> > > -			 * will not be used. So the dma can be unmapped
> > > -			 * if the ref is 0.
> > > -			 */
> > > -			virtnet_rq_unmap(rq, rq->last_dma, 0);
> > > -			rq->last_dma = NULL;
> > > -		}
> > > -
> > > -		dma->len = alloc_frag->size - sizeof(*dma);
> > > -
> > > -		addr = virtqueue_map_single_attrs(rq->vq, dma + 1,
> > > -						  dma->len, DMA_FROM_DEVICE, 0);
> > > -		if (virtqueue_map_mapping_error(rq->vq, addr))
> > > -			return NULL;
> > > -
> > > -		dma->addr = addr;
> > > -		dma->need_sync = virtqueue_map_need_sync(rq->vq, addr);
> > 
> > it gives me pause that this patch never does sync.
> > don't you need page_pool_dma_sync_for_cpu somewhere?
> 
> I missed the page_pool_dma_sync_for_cpu in the receive path before
> reading the buffer data. I will add it in v5.
> 
> > 
> > 
> > 
> > > -
> > > -		/* Add a reference to dma to prevent the entire dma from
> > > -		 * being released during error handling. This reference
> > > -		 * will be freed after the pages are no longer used.
> > > -		 */
> > > -		get_page(alloc_frag->page);
> > > -		dma->ref = 1;
> > > -		alloc_frag->offset = sizeof(*dma);
> > > -
> > > -		rq->last_dma = dma;
> > > -	}
> > > -
> > > -	++dma->ref;
> > > -
> > > -	buf = head + alloc_frag->offset;
> > > -
> > > -	get_page(alloc_frag->page);
> > > -	alloc_frag->offset += size;
> > > -
> > > -	return buf;
> > > +	return virtqueue_get_buf_ctx(rq->vq, len, ctx);
> > >   }
> > >   static void virtnet_rq_unmap_free_buf(struct virtqueue *vq, void *buf)
> > > @@ -1067,9 +1004,6 @@ static void virtnet_rq_unmap_free_buf(struct virtqueue *vq, void *buf)
> > >   		return;
> > >   	}
> > > -	if (!vi->big_packets || vi->mergeable_rx_bufs)
> > > -		virtnet_rq_unmap(rq, buf, 0);
> > > -
> > >   	virtnet_rq_free_buf(vi, rq, buf);
> > >   }
> > > @@ -1335,7 +1269,7 @@ static int xsk_append_merge_buffer(struct virtnet_info *vi,
> > >   		truesize = len;
> > > -		curr_skb  = virtnet_skb_append_frag(head_skb, curr_skb, page,
> > > +		curr_skb  = virtnet_skb_append_frag(rq, head_skb, curr_skb, page,
> > >   						    buf, len, truesize);
> > >   		if (!curr_skb) {
> > >   			put_page(page);
> > > @@ -1771,7 +1705,7 @@ static int virtnet_xdp_xmit(struct net_device *dev,
> > >   	return ret;
> > >   }
> > > -static void put_xdp_frags(struct xdp_buff *xdp)
> > > +static void put_xdp_frags(struct receive_queue *rq, struct xdp_buff *xdp)
> > >   {
> > >   	struct skb_shared_info *shinfo;
> > >   	struct page *xdp_page;
> > > @@ -1781,7 +1715,7 @@ static void put_xdp_frags(struct xdp_buff *xdp)
> > >   		shinfo = xdp_get_shared_info_from_buff(xdp);
> > >   		for (i = 0; i < shinfo->nr_frags; i++) {
> > >   			xdp_page = skb_frag_page(&shinfo->frags[i]);
> > > -			put_page(xdp_page);
> > > +			virtnet_put_page(rq, xdp_page, true);
> > >   		}
> > >   	}
> > >   }
> > > @@ -1873,7 +1807,7 @@ static struct page *xdp_linearize_page(struct net_device *dev,
> > >   	if (page_off + *len + tailroom > PAGE_SIZE)
> > >   		return NULL;
> > > -	page = alloc_page(GFP_ATOMIC);
> > > +	page = page_pool_alloc_pages(rq->page_pool, GFP_ATOMIC);
> > >   	if (!page)
> > >   		return NULL;
> > > @@ -1897,7 +1831,7 @@ static struct page *xdp_linearize_page(struct net_device *dev,
> > >   		off = buf - page_address(p);
> > >   		if (check_mergeable_len(dev, ctx, buflen)) {
> > > -			put_page(p);
> > > +			virtnet_put_page(rq, p, true);
> > >   			goto err_buf;
> > >   		}
> > > @@ -1905,21 +1839,21 @@ static struct page *xdp_linearize_page(struct net_device *dev,
> > >   		 * is sending packet larger than the MTU.
> > >   		 */
> > >   		if ((page_off + buflen + tailroom) > PAGE_SIZE) {
> > > -			put_page(p);
> > > +			virtnet_put_page(rq, p, true);
> > >   			goto err_buf;
> > >   		}
> > >   		memcpy(page_address(page) + page_off,
> > >   		       page_address(p) + off, buflen);
> > >   		page_off += buflen;
> > > -		put_page(p);
> > > +		virtnet_put_page(rq, p, true);
> > >   	}
> > >   	/* Headroom does not contribute to packet length */
> > >   	*len = page_off - XDP_PACKET_HEADROOM;
> > >   	return page;
> > >   err_buf:
> > > -	__free_pages(page, 0);
> > > +	page_pool_put_page(rq->page_pool, page, -1, true);
> > >   	return NULL;
> > >   }
> > > @@ -1996,7 +1930,7 @@ static struct sk_buff *receive_small_xdp(struct net_device *dev,
> > >   			goto err_xdp;
> > >   		buf = page_address(xdp_page);
> > > -		put_page(page);
> > > +		virtnet_put_page(rq, page, true);
> > >   		page = xdp_page;
> > >   	}
> > > @@ -2028,13 +1962,15 @@ static struct sk_buff *receive_small_xdp(struct net_device *dev,
> > >   	if (metasize)
> > >   		skb_metadata_set(skb, metasize);
> > > +	skb_mark_for_recycle(skb);
> > > +
> > >   	return skb;
> > >   err_xdp:
> > >   	u64_stats_inc(&stats->xdp_drops);
> > >   err:
> > >   	u64_stats_inc(&stats->drops);
> > > -	put_page(page);
> > > +	virtnet_put_page(rq, page, true);
> > >   xdp_xmit:
> > >   	return NULL;
> > >   }
> > > @@ -2082,12 +2018,14 @@ static struct sk_buff *receive_small(struct net_device *dev,
> > >   	}
> > >   	skb = receive_small_build_skb(vi, xdp_headroom, buf, len);
> > > -	if (likely(skb))
> > > +	if (likely(skb)) {
> > > +		skb_mark_for_recycle(skb);
> > >   		return skb;
> > > +	}
> > >   err:
> > >   	u64_stats_inc(&stats->drops);
> > > -	put_page(page);
> > > +	virtnet_put_page(rq, page, true);
> > >   	return NULL;
> > >   }
> > > @@ -2142,7 +2080,7 @@ static void mergeable_buf_free(struct receive_queue *rq, int num_buf,
> > >   		}
> > >   		u64_stats_add(&stats->bytes, len);
> > >   		page = virt_to_head_page(buf);
> > > -		put_page(page);
> > > +		virtnet_put_page(rq, page, true);
> > >   	}
> > >   }
> > > @@ -2253,7 +2191,7 @@ static int virtnet_build_xdp_buff_mrg(struct net_device *dev,
> > >   		offset = buf - page_address(page);
> > >   		if (check_mergeable_len(dev, ctx, len)) {
> > > -			put_page(page);
> > > +			virtnet_put_page(rq, page, true);
> > >   			goto err;
> > >   		}
> > > @@ -2272,7 +2210,7 @@ static int virtnet_build_xdp_buff_mrg(struct net_device *dev,
> > >   	return 0;
> > >   err:
> > > -	put_xdp_frags(xdp);
> > > +	put_xdp_frags(rq, xdp);
> > >   	return -EINVAL;
> > >   }
> > > @@ -2337,7 +2275,7 @@ static void *mergeable_xdp_get_buf(struct virtnet_info *vi,
> > >   		if (*len + xdp_room > PAGE_SIZE)
> > >   			return NULL;
> > > -		xdp_page = alloc_page(GFP_ATOMIC);
> > > +		xdp_page = page_pool_alloc_pages(rq->page_pool, GFP_ATOMIC);
> > >   		if (!xdp_page)
> > >   			return NULL;
> > > @@ -2347,7 +2285,7 @@ static void *mergeable_xdp_get_buf(struct virtnet_info *vi,
> > >   	*frame_sz = PAGE_SIZE;
> > > -	put_page(*page);
> > > +	virtnet_put_page(rq, *page, true);
> > >   	*page = xdp_page;
> > > @@ -2393,6 +2331,8 @@ static struct sk_buff *receive_mergeable_xdp(struct net_device *dev,
> > >   		head_skb = build_skb_from_xdp_buff(dev, vi, &xdp, xdp_frags_truesz);
> > >   		if (unlikely(!head_skb))
> > >   			break;
> > > +
> > > +		skb_mark_for_recycle(head_skb);
> > >   		return head_skb;
> > >   	case XDP_TX:
> > > @@ -2403,10 +2343,10 @@ static struct sk_buff *receive_mergeable_xdp(struct net_device *dev,
> > >   		break;
> > >   	}
> > > -	put_xdp_frags(&xdp);
> > > +	put_xdp_frags(rq, &xdp);
> > >   err_xdp:
> > > -	put_page(page);
> > > +	virtnet_put_page(rq, page, true);
> > >   	mergeable_buf_free(rq, num_buf, dev, stats);
> > >   	u64_stats_inc(&stats->xdp_drops);
> > > @@ -2414,7 +2354,8 @@ static struct sk_buff *receive_mergeable_xdp(struct net_device *dev,
> > >   	return NULL;
> > >   }
> > > -static struct sk_buff *virtnet_skb_append_frag(struct sk_buff *head_skb,
> > > +static struct sk_buff *virtnet_skb_append_frag(struct receive_queue *rq,
> > > +					       struct sk_buff *head_skb,
> > >   					       struct sk_buff *curr_skb,
> > >   					       struct page *page, void *buf,
> > >   					       int len, int truesize)
> > > @@ -2446,7 +2387,7 @@ static struct sk_buff *virtnet_skb_append_frag(struct sk_buff *head_skb,
> > >   	offset = buf - page_address(page);
> > >   	if (skb_can_coalesce(curr_skb, num_skb_frags, page, offset)) {
> > > -		put_page(page);
> > > +		virtnet_put_page(rq, page, true);
> > >   		skb_coalesce_rx_frag(curr_skb, num_skb_frags - 1,
> > >   				     len, truesize);
> > >   	} else {
> > > @@ -2499,6 +2440,8 @@ static struct sk_buff *receive_mergeable(struct net_device *dev,
> > >   	if (unlikely(!curr_skb))
> > >   		goto err_skb;
> > > +
> > > +	skb_mark_for_recycle(head_skb);
> > >   	while (--num_buf) {
> > >   		buf = virtnet_rq_get_buf(rq, &len, &ctx);
> > >   		if (unlikely(!buf)) {
> > > @@ -2517,7 +2460,7 @@ static struct sk_buff *receive_mergeable(struct net_device *dev,
> > >   			goto err_skb;
> > >   		truesize = mergeable_ctx_to_truesize(ctx);
> > > -		curr_skb  = virtnet_skb_append_frag(head_skb, curr_skb, page,
> > > +		curr_skb  = virtnet_skb_append_frag(rq, head_skb, curr_skb, page,
> > >   						    buf, len, truesize);
> > >   		if (!curr_skb)
> > >   			goto err_skb;
> > > @@ -2527,7 +2470,7 @@ static struct sk_buff *receive_mergeable(struct net_device *dev,
> > >   	return head_skb;
> > >   err_skb:
> > > -	put_page(page);
> > > +	virtnet_put_page(rq, page, true);
> > >   	mergeable_buf_free(rq, num_buf, dev, stats);
> > >   err_buf:
> > > @@ -2666,32 +2609,42 @@ static void receive_buf(struct virtnet_info *vi, struct receive_queue *rq,
> > >   static int add_recvbuf_small(struct virtnet_info *vi, struct receive_queue *rq,
> > >   			     gfp_t gfp)
> > >   {
> > > -	char *buf;
> > >   	unsigned int xdp_headroom = virtnet_get_headroom(vi);
> > >   	void *ctx = (void *)(unsigned long)xdp_headroom;
> > >   	int len = vi->hdr_len + VIRTNET_RX_PAD + GOOD_PACKET_LEN + xdp_headroom;
> > > +	unsigned int offset;
> > > +	struct page *page;
> > > +	dma_addr_t addr;
> > > +	char *buf;
> > >   	int err;
> > >   	len = SKB_DATA_ALIGN(len) +
> > >   	      SKB_DATA_ALIGN(sizeof(struct skb_shared_info));
> > > -	if (unlikely(!skb_page_frag_refill(len, &rq->alloc_frag, gfp)))
> > > -		return -ENOMEM;
> > > -
> > > -	buf = virtnet_rq_alloc(rq, len, gfp);
> > > -	if (unlikely(!buf))
> > > +	page = page_pool_alloc_frag(rq->page_pool, &offset, len, gfp);
> > > +	if (unlikely(!page))
> > >   		return -ENOMEM;
> > > +	buf = page_address(page) + offset;
> > >   	buf += VIRTNET_RX_PAD + xdp_headroom;
> > > -	virtnet_rq_init_one_sg(rq, buf, vi->hdr_len + GOOD_PACKET_LEN);
> > > +	if (rq->use_page_pool_dma) {
> > > +		addr = page_pool_get_dma_addr(page) + offset;
> > > +		addr += VIRTNET_RX_PAD + xdp_headroom;
> > > -	err = virtqueue_add_inbuf_premapped(rq->vq, rq->sg, 1, buf, ctx, gfp);
> > > -	if (err < 0) {
> > > -		virtnet_rq_unmap(rq, buf, 0);
> > > -		put_page(virt_to_head_page(buf));
> > > +		sg_init_table(rq->sg, 1);
> > > +		sg_fill_dma(rq->sg, addr, vi->hdr_len + GOOD_PACKET_LEN);
> > > +		err = virtqueue_add_inbuf_premapped(rq->vq, rq->sg, 1,
> > > +						    buf, ctx, gfp);
> > > +	} else {
> > > +		sg_init_one(rq->sg, buf, vi->hdr_len + GOOD_PACKET_LEN);
> > > +		err = virtqueue_add_inbuf_ctx(rq->vq, rq->sg, 1,
> > > +					      buf, ctx, gfp);
> > >   	}
> > > +	if (err < 0)
> > > +		page_pool_put_page(rq->page_pool, virt_to_head_page(buf),
> > > +				   -1, false);
> > >   	return err;
> > >   }
> > > @@ -2764,13 +2717,15 @@ static unsigned int get_mergeable_buf_len(struct receive_queue *rq,
> > >   static int add_recvbuf_mergeable(struct virtnet_info *vi,
> > >   				 struct receive_queue *rq, gfp_t gfp)
> > >   {
> > > -	struct page_frag *alloc_frag = &rq->alloc_frag;
> > >   	unsigned int headroom = virtnet_get_headroom(vi);
> > >   	unsigned int tailroom = headroom ? sizeof(struct skb_shared_info) : 0;
> > >   	unsigned int room = SKB_DATA_ALIGN(headroom + tailroom);
> > >   	unsigned int len, hole;
> > > -	void *ctx;
> > > +	unsigned int offset;
> > > +	struct page *page;
> > > +	dma_addr_t addr;
> > >   	char *buf;
> > > +	void *ctx;
> > >   	int err;
> > >   	/* Extra tailroom is needed to satisfy XDP's assumption. This
> > > @@ -2779,18 +2734,14 @@ static int add_recvbuf_mergeable(struct virtnet_info *vi,
> > >   	 */
> > >   	len = get_mergeable_buf_len(rq, &rq->mrg_avg_pkt_len, room);
> > > -	if (unlikely(!skb_page_frag_refill(len + room, alloc_frag, gfp)))
> > > -		return -ENOMEM;
> > > -
> > > -	if (!alloc_frag->offset && len + room + sizeof(struct virtnet_rq_dma) > alloc_frag->size)
> > > -		len -= sizeof(struct virtnet_rq_dma);
> > > -
> > > -	buf = virtnet_rq_alloc(rq, len + room, gfp);
> > > -	if (unlikely(!buf))
> > > +	page = page_pool_alloc_frag(rq->page_pool, &offset, len + room, gfp);
> > > +	if (unlikely(!page))
> > >   		return -ENOMEM;
> > > +	buf = page_address(page) + offset;
> > >   	buf += headroom; /* advance address leaving hole at front of pkt */
> > > -	hole = alloc_frag->size - alloc_frag->offset;
> > > +
> > > +	hole = PAGE_SIZE - (offset + len + room);
> > >   	if (hole < len + room) {
> > >   		/* To avoid internal fragmentation, if there is very likely not
> > >   		 * enough space for another buffer, add the remaining space to
> > > @@ -2800,18 +2751,27 @@ static int add_recvbuf_mergeable(struct virtnet_info *vi,
> > >   		 */
> > >   		if (!headroom)
> > >   			len += hole;
> > > -		alloc_frag->offset += hole;
> > 
> > Hmm. All these allocations are tricky.
> > So we used to advance offset by hole but with page pool api
> > what advances pool->frag_offset? If nothing will not the next
> > small allocation reuse the space and overlap the buffer?
> 
> I tested with debug tracing and confirmed the issue triggers with
> typical 1536-byte allocations. When len += hole extends the buffer into
> 3072-4096, page_pool's internal frag_offset stays at 3072, so a
> subsequent smaller allocation could overlap.
> Since page_pool manages frag_offset internally and there's no API to
> advance it past the hole, the fix is to remove the if (hole < len +
> room) block entirely.

Well... but this means that fragmentation can waste memory
which is not accounted for anywhere. Just add an API for this?


> > 
> > 
> > >   	}
> > > -	virtnet_rq_init_one_sg(rq, buf, len);
> > > -
> > >   	ctx = mergeable_len_to_ctx(len + room, headroom);
> > > -	err = virtqueue_add_inbuf_premapped(rq->vq, rq->sg, 1, buf, ctx, gfp);
> > > -	if (err < 0) {
> > > -		virtnet_rq_unmap(rq, buf, 0);
> > > -		put_page(virt_to_head_page(buf));
> > > +
> > > +	if (rq->use_page_pool_dma) {
> > > +		addr = page_pool_get_dma_addr(page) + offset;
> > > +		addr += headroom;
> > > +
> > > +		sg_init_table(rq->sg, 1);
> > > +		sg_fill_dma(rq->sg, addr, len);
> > > +		err = virtqueue_add_inbuf_premapped(rq->vq, rq->sg, 1,
> > > +						    buf, ctx, gfp);
> > > +	} else {
> > > +		sg_init_one(rq->sg, buf, len);
> > > +		err = virtqueue_add_inbuf_ctx(rq->vq, rq->sg, 1,
> > > +					      buf, ctx, gfp);
> > >   	}
> > > +	if (err < 0)
> > > +		page_pool_put_page(rq->page_pool, virt_to_head_page(buf),
> > > +				   -1, false);
> > >   	return err;
> > >   }
> > > @@ -3128,7 +3088,10 @@ static int virtnet_enable_queue_pair(struct virtnet_info *vi, int qp_index)
> > >   		return err;
> > >   	err = xdp_rxq_info_reg_mem_model(&vi->rq[qp_index].xdp_rxq,
> > > -					 MEM_TYPE_PAGE_SHARED, NULL);
> > > +					 vi->rq[qp_index].page_pool ?
> > > +						MEM_TYPE_PAGE_POOL :
> > > +						MEM_TYPE_PAGE_SHARED,
> > > +					 vi->rq[qp_index].page_pool);
> > >   	if (err < 0)
> > >   		goto err_xdp_reg_mem_model;
> > > @@ -3168,6 +3131,81 @@ static void virtnet_update_settings(struct virtnet_info *vi)
> > >   		vi->duplex = duplex;
> > >   }
> > > +static int virtnet_create_page_pools(struct virtnet_info *vi)
> > > +{
> > > +	int i, err;
> > > +
> > > +	if (!vi->mergeable_rx_bufs && vi->big_packets)
> > > +		return 0;
> > > +
> > > +	for (i = 0; i < vi->max_queue_pairs; i++) {
> > > +		struct receive_queue *rq = &vi->rq[i];
> > > +		struct page_pool_params pp_params = { 0 };
> > > +		struct device *dma_dev;
> > > +
> > > +		if (rq->page_pool)
> > > +			continue;
> > > +
> > > +		if (rq->xsk_pool)
> > > +			continue;
> > > +
> > > +		pp_params.order = 0;
> > > +		pp_params.pool_size = virtqueue_get_vring_size(rq->vq);
> > > +		pp_params.nid = dev_to_node(vi->vdev->dev.parent);
> > > +		pp_params.netdev = vi->dev;
> > > +		pp_params.napi = &rq->napi;
> > > +
> > > +		/* Check if backend supports DMA API (e.g., vhost, virtio-pci).
> > > +		 * If so, use page_pool's DMA mapping for premapped buffers.
> > > +		 * Otherwise (e.g., VDUSE), page_pool only handles allocation.
> > > +		 */
> > > +		dma_dev = virtqueue_dma_dev(rq->vq);
> > > +		if (dma_dev) {
> > > +			pp_params.dev = dma_dev;
> > > +			pp_params.flags = PP_FLAG_DMA_MAP;
> > > +			pp_params.dma_dir = DMA_FROM_DEVICE;
> > > +			rq->use_page_pool_dma = true;
> > > +		} else {
> > > +			pp_params.dev = vi->vdev->dev.parent;
> > > +			pp_params.flags = 0;
> > > +			rq->use_page_pool_dma = false;
> > > +		}
> > > +
> > > +		rq->page_pool = page_pool_create(&pp_params);
> > > +		if (IS_ERR(rq->page_pool)) {
> > > +			err = PTR_ERR(rq->page_pool);
> > > +			rq->page_pool = NULL;
> > > +			goto err_cleanup;
> > > +		}
> > > +	}
> > > +	return 0;
> > > +
> > > +err_cleanup:
> > > +	while (--i >= 0) {
> > > +		struct receive_queue *rq = &vi->rq[i];
> > > +
> > > +		if (rq->page_pool) {
> > > +			page_pool_destroy(rq->page_pool);
> > > +			rq->page_pool = NULL;
> > > +		}
> > > +	}
> > > +	return err;
> > > +}
> > > +
> > > +static void virtnet_destroy_page_pools(struct virtnet_info *vi)
> > > +{
> > > +	int i;
> > > +
> > > +	for (i = 0; i < vi->max_queue_pairs; i++) {
> > > +		struct receive_queue *rq = &vi->rq[i];
> > > +
> > > +		if (rq->page_pool) {
> > > +			page_pool_destroy(rq->page_pool);
> > > +			rq->page_pool = NULL;
> > > +		}
> > > +	}
> > > +}
> > > +
> > >   static int virtnet_open(struct net_device *dev)
> > >   {
> > >   	struct virtnet_info *vi = netdev_priv(dev);
> > > @@ -6441,10 +6479,8 @@ static int virtnet_find_vqs(struct virtnet_info *vi)
> > >   		vi->rq[i].min_buf_len = mergeable_min_buf_len(vi, vi->rq[i].vq);
> > >   		vi->sq[i].vq = vqs[txq2vq(i)];
> > >   	}
> > > -
> > >   	/* run here: ret == 0. */
> > > -
> > >   err_find:
> > >   	kfree(ctx);
> > >   err_ctx:
> > > @@ -6945,6 +6981,14 @@ static int virtnet_probe(struct virtio_device *vdev)
> > >   			goto free;
> > >   	}
> > > +	/* Create page pools for receive queues.
> > > +	 * Page pools are created at probe time so they can be used
> > > +	 * with premapped DMA addresses throughout the device lifetime.
> > > +	 */
> > > +	err = virtnet_create_page_pools(vi);
> > > +	if (err)
> > > +		goto free_irq_moder;
> > > +
> > >   #ifdef CONFIG_SYSFS
> > >   	if (vi->mergeable_rx_bufs)
> > >   		dev->sysfs_rx_queue_group = &virtio_net_mrg_rx_group;
> > > @@ -6958,7 +7002,7 @@ static int virtnet_probe(struct virtio_device *vdev)
> > >   		vi->failover = net_failover_create(vi->dev);
> > >   		if (IS_ERR(vi->failover)) {
> > >   			err = PTR_ERR(vi->failover);
> > > -			goto free_vqs;
> > > +			goto free_page_pools;
> > >   		}
> > >   	}
> > > @@ -7075,7 +7119,10 @@ static int virtnet_probe(struct virtio_device *vdev)
> > >   	unregister_netdev(dev);
> > >   free_failover:
> > >   	net_failover_destroy(vi->failover);
> > > -free_vqs:
> > > +free_page_pools:
> > > +	virtnet_destroy_page_pools(vi);
> > > +free_irq_moder:
> > > +	virtnet_free_irq_moder(vi);
> > >   	virtio_reset_device(vdev);
> > >   	free_receive_page_frags(vi);
> > >   	virtnet_del_vqs(vi);
> > > @@ -7104,6 +7151,8 @@ static void remove_vq_common(struct virtnet_info *vi)
> > >   	free_receive_page_frags(vi);
> > > +	virtnet_destroy_page_pools(vi);
> > > +
> > >   	virtnet_del_vqs(vi);
> > >   }
> > > -- 
> > > 2.47.3
> >

Re: [PATCH net-next v4 1/2] virtio_net: add page_pool support for buffer allocation

Posted by Vishwanath Seshagiri 3 days, 2 hours ago


On 2/4/26 10:40 PM, Michael S. Tsirkin wrote:
> On Wed, Feb 04, 2026 at 10:34:38PM -0800, Vishwanath Seshagiri wrote:
>>
>>
>> On 2/4/26 9:30 PM, Michael S. Tsirkin wrote:
>>> On Wed, Feb 04, 2026 at 11:36:16AM -0800, Vishwanath Seshagiri wrote:
>>>> Use page_pool for RX buffer allocation in mergeable and small buffer
>>>> modes to enable page recycling and avoid repeated page allocator calls.
>>>> skb_mark_for_recycle() enables page reuse in the network stack.
>>>>
>>>> Big packets mode is unchanged because it uses page->private for linked
>>>> list chaining of multiple pages per buffer, which conflicts with
>>>> page_pool's internal use of page->private.
>>>>
>>>> Implement conditional DMA premapping using virtqueue_dma_dev():
>>>> - When non-NULL (vhost, virtio-pci): use PP_FLAG_DMA_MAP with page_pool
>>>>     handling DMA mapping, submit via virtqueue_add_inbuf_premapped()
>>>> - When NULL (VDUSE, direct physical): page_pool handles allocation only,
>>>>     submit via virtqueue_add_inbuf_ctx()
>>>>
>>>> This preserves the DMA premapping optimization from commit 31f3cd4e5756b
>>>> ("virtio-net: rq submits premapped per-buffer") while adding page_pool
>>>> support as a prerequisite for future zero-copy features (devmem TCP,
>>>> io_uring ZCRX).
>>>>
>>>> Page pools are created in probe and destroyed in remove (not open/close),
>>>> following existing driver behavior where RX buffers remain in virtqueues
>>>> across interface state changes.
>>>>
>>>> Signed-off-by: Vishwanath Seshagiri <vishs@meta.com>
>>>> ---
>>>>    drivers/net/Kconfig      |   1 +
>>>>    drivers/net/virtio_net.c | 351 ++++++++++++++++++++++-----------------
>>>>    2 files changed, 201 insertions(+), 151 deletions(-)
>>>>
>>>> diff --git a/drivers/net/Kconfig b/drivers/net/Kconfig
>>>> index ac12eaf11755..f1e6b6b0a86f 100644
>>>> --- a/drivers/net/Kconfig
>>>> +++ b/drivers/net/Kconfig
>>>> @@ -450,6 +450,7 @@ config VIRTIO_NET
>>>>    	depends on VIRTIO
>>>>    	select NET_FAILOVER
>>>>    	select DIMLIB
>>>> +	select PAGE_POOL
>>>>    	help
>>>>    	  This is the virtual network driver for virtio.  It can be used with
>>>>    	  QEMU based VMMs (like KVM or Xen).  Say Y or M.
>>>> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
>>>> index db88dcaefb20..74c51e597c3f 100644
>>>> --- a/drivers/net/virtio_net.c
>>>> +++ b/drivers/net/virtio_net.c
>>>> @@ -26,6 +26,7 @@
>>>>    #include <net/netdev_rx_queue.h>
>>>>    #include <net/netdev_queues.h>
>>>>    #include <net/xdp_sock_drv.h>
>>>> +#include <net/page_pool/helpers.h>
>>>>    static int napi_weight = NAPI_POLL_WEIGHT;
>>>>    module_param(napi_weight, int, 0444);
>>>> @@ -359,6 +360,11 @@ struct receive_queue {
>>>>    	/* Page frag for packet buffer allocation. */
>>>>    	struct page_frag alloc_frag;
>>>> +	struct page_pool *page_pool;
>>>> +
>>>> +	/* True if page_pool handles DMA mapping via PP_FLAG_DMA_MAP */
>>>> +	bool use_page_pool_dma;
>>>> +
>>>>    	/* RX: fragments + linear part + virtio header */
>>>>    	struct scatterlist sg[MAX_SKB_FRAGS + 2];
>>>> @@ -521,11 +527,13 @@ static int virtnet_xdp_handler(struct bpf_prog *xdp_prog, struct xdp_buff *xdp,
>>>>    			       struct virtnet_rq_stats *stats);
>>>>    static void virtnet_receive_done(struct virtnet_info *vi, struct receive_queue *rq,
>>>>    				 struct sk_buff *skb, u8 flags);
>>>> -static struct sk_buff *virtnet_skb_append_frag(struct sk_buff *head_skb,
>>>> +static struct sk_buff *virtnet_skb_append_frag(struct receive_queue *rq,
>>>> +					       struct sk_buff *head_skb,
>>>>    					       struct sk_buff *curr_skb,
>>>>    					       struct page *page, void *buf,
>>>>    					       int len, int truesize);
>>>>    static void virtnet_xsk_completed(struct send_queue *sq, int num);
>>>> +static void free_unused_bufs(struct virtnet_info *vi);
>>>>    enum virtnet_xmit_type {
>>>>    	VIRTNET_XMIT_TYPE_SKB,
>>>> @@ -706,15 +714,24 @@ static struct page *get_a_page(struct receive_queue *rq, gfp_t gfp_mask)
>>>>    	return p;
>>>>    }
>>>> +static void virtnet_put_page(struct receive_queue *rq, struct page *page,
>>>> +			     bool allow_direct)
>>>> +{
>>>> +	if (page_pool_page_is_pp(page))
>>>> +		page_pool_put_page(rq->page_pool, page, -1, allow_direct);
>>>> +	else
>>>> +		put_page(page);
>>>> +}
>>>> +
>>>>    static void virtnet_rq_free_buf(struct virtnet_info *vi,
>>>>    				struct receive_queue *rq, void *buf)
>>>>    {
>>>>    	if (vi->mergeable_rx_bufs)
>>>> -		put_page(virt_to_head_page(buf));
>>>> +		virtnet_put_page(rq, virt_to_head_page(buf), false);
>>>>    	else if (vi->big_packets)
>>>>    		give_pages(rq, buf);
>>>>    	else
>>>> -		put_page(virt_to_head_page(buf));
>>>> +		virtnet_put_page(rq, virt_to_head_page(buf), false);
>>>>    }
>>>>    static void enable_rx_mode_work(struct virtnet_info *vi)
>>>> @@ -877,9 +894,12 @@ static struct sk_buff *page_to_skb(struct virtnet_info *vi,
>>>>    		if (unlikely(!skb))
>>>>    			return NULL;
>>>> -		page = (struct page *)page->private;
>>>> -		if (page)
>>>> -			give_pages(rq, page);
>>>> +		if (!rq->page_pool) {
>>>
>>> I think this is ok because big_packets is exactly when this happens.
>>> but it is confusing that the conditions on free and alloc are
>>> written differently. A comment with an explanation, at least?
>>
>> I will add a comment here in v5.
> 
> Would be better to also unify the way we test on alloc and free paths,
> if possible.

Yeah, I can unify the checks wherever possible, and will add a comment
when I cannot make the changes.

> 
> 
>>>
>>>
>>>> +			page = (struct page *)page->private;
>>>> +			if (page)
>>>> +				give_pages(rq, page);
>>>> +		}
>>>> +
>>>>    		goto ok;
>>>>    	}
>>>> @@ -925,7 +945,7 @@ static struct sk_buff *page_to_skb(struct virtnet_info *vi,
>>>>    	hdr = skb_vnet_common_hdr(skb);
>>>>    	memcpy(hdr, hdr_p, hdr_len);
>>>>    	if (page_to_free)
>>>> -		put_page(page_to_free);
>>>> +		virtnet_put_page(rq, page_to_free, true);
>>>>    	return skb;
>>>>    }
>>>> @@ -965,93 +985,10 @@ static void virtnet_rq_unmap(struct receive_queue *rq, void *buf, u32 len)
>>>>    static void *virtnet_rq_get_buf(struct receive_queue *rq, u32 *len, void **ctx)
>>>>    {
>>>>    	struct virtnet_info *vi = rq->vq->vdev->priv;
>>>> -	void *buf;
>>>> -
>>>> -	BUG_ON(vi->big_packets && !vi->mergeable_rx_bufs);
>>>> -
>>>> -	buf = virtqueue_get_buf_ctx(rq->vq, len, ctx);
>>>> -	if (buf)
>>>> -		virtnet_rq_unmap(rq, buf, *len);
>>>> -
>>>> -	return buf;
>>>> -}
>>>> -
>>>> -static void virtnet_rq_init_one_sg(struct receive_queue *rq, void *buf, u32 len)
>>>> -{
>>>> -	struct virtnet_info *vi = rq->vq->vdev->priv;
>>>> -	struct virtnet_rq_dma *dma;
>>>> -	dma_addr_t addr;
>>>> -	u32 offset;
>>>> -	void *head;
>>>> -
>>>> -	BUG_ON(vi->big_packets && !vi->mergeable_rx_bufs);
>>>> -
>>>> -	head = page_address(rq->alloc_frag.page);
>>>> -
>>>> -	offset = buf - head;
>>>> -
>>>> -	dma = head;
>>>> -
>>>> -	addr = dma->addr - sizeof(*dma) + offset;
>>>> -
>>>> -	sg_init_table(rq->sg, 1);
>>>> -	sg_fill_dma(rq->sg, addr, len);
>>>> -}
>>>> -
>>>> -static void *virtnet_rq_alloc(struct receive_queue *rq, u32 size, gfp_t gfp)
>>>> -{
>>>> -	struct page_frag *alloc_frag = &rq->alloc_frag;
>>>> -	struct virtnet_info *vi = rq->vq->vdev->priv;
>>>> -	struct virtnet_rq_dma *dma;
>>>> -	void *buf, *head;
>>>> -	dma_addr_t addr;
>>>>    	BUG_ON(vi->big_packets && !vi->mergeable_rx_bufs);
>>>> -	head = page_address(alloc_frag->page);
>>>> -
>>>> -	dma = head;
>>>> -
>>>> -	/* new pages */
>>>> -	if (!alloc_frag->offset) {
>>>> -		if (rq->last_dma) {
>>>> -			/* Now, the new page is allocated, the last dma
>>>> -			 * will not be used. So the dma can be unmapped
>>>> -			 * if the ref is 0.
>>>> -			 */
>>>> -			virtnet_rq_unmap(rq, rq->last_dma, 0);
>>>> -			rq->last_dma = NULL;
>>>> -		}
>>>> -
>>>> -		dma->len = alloc_frag->size - sizeof(*dma);
>>>> -
>>>> -		addr = virtqueue_map_single_attrs(rq->vq, dma + 1,
>>>> -						  dma->len, DMA_FROM_DEVICE, 0);
>>>> -		if (virtqueue_map_mapping_error(rq->vq, addr))
>>>> -			return NULL;
>>>> -
>>>> -		dma->addr = addr;
>>>> -		dma->need_sync = virtqueue_map_need_sync(rq->vq, addr);
>>>
>>> it gives me pause that this patch never does sync.
>>> don't you need page_pool_dma_sync_for_cpu somewhere?
>>
>> I missed the page_pool_dma_sync_for_cpu in the receive path before
>> reading the buffer data. I will add it in v5.
>>
>>>
>>>
>>>
>>>> -
>>>> -		/* Add a reference to dma to prevent the entire dma from
>>>> -		 * being released during error handling. This reference
>>>> -		 * will be freed after the pages are no longer used.
>>>> -		 */
>>>> -		get_page(alloc_frag->page);
>>>> -		dma->ref = 1;
>>>> -		alloc_frag->offset = sizeof(*dma);
>>>> -
>>>> -		rq->last_dma = dma;
>>>> -	}
>>>> -
>>>> -	++dma->ref;
>>>> -
>>>> -	buf = head + alloc_frag->offset;
>>>> -
>>>> -	get_page(alloc_frag->page);
>>>> -	alloc_frag->offset += size;
>>>> -
>>>> -	return buf;
>>>> +	return virtqueue_get_buf_ctx(rq->vq, len, ctx);
>>>>    }
>>>>    static void virtnet_rq_unmap_free_buf(struct virtqueue *vq, void *buf)
>>>> @@ -1067,9 +1004,6 @@ static void virtnet_rq_unmap_free_buf(struct virtqueue *vq, void *buf)
>>>>    		return;
>>>>    	}
>>>> -	if (!vi->big_packets || vi->mergeable_rx_bufs)
>>>> -		virtnet_rq_unmap(rq, buf, 0);
>>>> -
>>>>    	virtnet_rq_free_buf(vi, rq, buf);
>>>>    }
>>>> @@ -1335,7 +1269,7 @@ static int xsk_append_merge_buffer(struct virtnet_info *vi,
>>>>    		truesize = len;
>>>> -		curr_skb  = virtnet_skb_append_frag(head_skb, curr_skb, page,
>>>> +		curr_skb  = virtnet_skb_append_frag(rq, head_skb, curr_skb, page,
>>>>    						    buf, len, truesize);
>>>>    		if (!curr_skb) {
>>>>    			put_page(page);
>>>> @@ -1771,7 +1705,7 @@ static int virtnet_xdp_xmit(struct net_device *dev,
>>>>    	return ret;
>>>>    }
>>>> -static void put_xdp_frags(struct xdp_buff *xdp)
>>>> +static void put_xdp_frags(struct receive_queue *rq, struct xdp_buff *xdp)
>>>>    {
>>>>    	struct skb_shared_info *shinfo;
>>>>    	struct page *xdp_page;
>>>> @@ -1781,7 +1715,7 @@ static void put_xdp_frags(struct xdp_buff *xdp)
>>>>    		shinfo = xdp_get_shared_info_from_buff(xdp);
>>>>    		for (i = 0; i < shinfo->nr_frags; i++) {
>>>>    			xdp_page = skb_frag_page(&shinfo->frags[i]);
>>>> -			put_page(xdp_page);
>>>> +			virtnet_put_page(rq, xdp_page, true);
>>>>    		}
>>>>    	}
>>>>    }
>>>> @@ -1873,7 +1807,7 @@ static struct page *xdp_linearize_page(struct net_device *dev,
>>>>    	if (page_off + *len + tailroom > PAGE_SIZE)
>>>>    		return NULL;
>>>> -	page = alloc_page(GFP_ATOMIC);
>>>> +	page = page_pool_alloc_pages(rq->page_pool, GFP_ATOMIC);
>>>>    	if (!page)
>>>>    		return NULL;
>>>> @@ -1897,7 +1831,7 @@ static struct page *xdp_linearize_page(struct net_device *dev,
>>>>    		off = buf - page_address(p);
>>>>    		if (check_mergeable_len(dev, ctx, buflen)) {
>>>> -			put_page(p);
>>>> +			virtnet_put_page(rq, p, true);
>>>>    			goto err_buf;
>>>>    		}
>>>> @@ -1905,21 +1839,21 @@ static struct page *xdp_linearize_page(struct net_device *dev,
>>>>    		 * is sending packet larger than the MTU.
>>>>    		 */
>>>>    		if ((page_off + buflen + tailroom) > PAGE_SIZE) {
>>>> -			put_page(p);
>>>> +			virtnet_put_page(rq, p, true);
>>>>    			goto err_buf;
>>>>    		}
>>>>    		memcpy(page_address(page) + page_off,
>>>>    		       page_address(p) + off, buflen);
>>>>    		page_off += buflen;
>>>> -		put_page(p);
>>>> +		virtnet_put_page(rq, p, true);
>>>>    	}
>>>>    	/* Headroom does not contribute to packet length */
>>>>    	*len = page_off - XDP_PACKET_HEADROOM;
>>>>    	return page;
>>>>    err_buf:
>>>> -	__free_pages(page, 0);
>>>> +	page_pool_put_page(rq->page_pool, page, -1, true);
>>>>    	return NULL;
>>>>    }
>>>> @@ -1996,7 +1930,7 @@ static struct sk_buff *receive_small_xdp(struct net_device *dev,
>>>>    			goto err_xdp;
>>>>    		buf = page_address(xdp_page);
>>>> -		put_page(page);
>>>> +		virtnet_put_page(rq, page, true);
>>>>    		page = xdp_page;
>>>>    	}
>>>> @@ -2028,13 +1962,15 @@ static struct sk_buff *receive_small_xdp(struct net_device *dev,
>>>>    	if (metasize)
>>>>    		skb_metadata_set(skb, metasize);
>>>> +	skb_mark_for_recycle(skb);
>>>> +
>>>>    	return skb;
>>>>    err_xdp:
>>>>    	u64_stats_inc(&stats->xdp_drops);
>>>>    err:
>>>>    	u64_stats_inc(&stats->drops);
>>>> -	put_page(page);
>>>> +	virtnet_put_page(rq, page, true);
>>>>    xdp_xmit:
>>>>    	return NULL;
>>>>    }
>>>> @@ -2082,12 +2018,14 @@ static struct sk_buff *receive_small(struct net_device *dev,
>>>>    	}
>>>>    	skb = receive_small_build_skb(vi, xdp_headroom, buf, len);
>>>> -	if (likely(skb))
>>>> +	if (likely(skb)) {
>>>> +		skb_mark_for_recycle(skb);
>>>>    		return skb;
>>>> +	}
>>>>    err:
>>>>    	u64_stats_inc(&stats->drops);
>>>> -	put_page(page);
>>>> +	virtnet_put_page(rq, page, true);
>>>>    	return NULL;
>>>>    }
>>>> @@ -2142,7 +2080,7 @@ static void mergeable_buf_free(struct receive_queue *rq, int num_buf,
>>>>    		}
>>>>    		u64_stats_add(&stats->bytes, len);
>>>>    		page = virt_to_head_page(buf);
>>>> -		put_page(page);
>>>> +		virtnet_put_page(rq, page, true);
>>>>    	}
>>>>    }
>>>> @@ -2253,7 +2191,7 @@ static int virtnet_build_xdp_buff_mrg(struct net_device *dev,
>>>>    		offset = buf - page_address(page);
>>>>    		if (check_mergeable_len(dev, ctx, len)) {
>>>> -			put_page(page);
>>>> +			virtnet_put_page(rq, page, true);
>>>>    			goto err;
>>>>    		}
>>>> @@ -2272,7 +2210,7 @@ static int virtnet_build_xdp_buff_mrg(struct net_device *dev,
>>>>    	return 0;
>>>>    err:
>>>> -	put_xdp_frags(xdp);
>>>> +	put_xdp_frags(rq, xdp);
>>>>    	return -EINVAL;
>>>>    }
>>>> @@ -2337,7 +2275,7 @@ static void *mergeable_xdp_get_buf(struct virtnet_info *vi,
>>>>    		if (*len + xdp_room > PAGE_SIZE)
>>>>    			return NULL;
>>>> -		xdp_page = alloc_page(GFP_ATOMIC);
>>>> +		xdp_page = page_pool_alloc_pages(rq->page_pool, GFP_ATOMIC);
>>>>    		if (!xdp_page)
>>>>    			return NULL;
>>>> @@ -2347,7 +2285,7 @@ static void *mergeable_xdp_get_buf(struct virtnet_info *vi,
>>>>    	*frame_sz = PAGE_SIZE;
>>>> -	put_page(*page);
>>>> +	virtnet_put_page(rq, *page, true);
>>>>    	*page = xdp_page;
>>>> @@ -2393,6 +2331,8 @@ static struct sk_buff *receive_mergeable_xdp(struct net_device *dev,
>>>>    		head_skb = build_skb_from_xdp_buff(dev, vi, &xdp, xdp_frags_truesz);
>>>>    		if (unlikely(!head_skb))
>>>>    			break;
>>>> +
>>>> +		skb_mark_for_recycle(head_skb);
>>>>    		return head_skb;
>>>>    	case XDP_TX:
>>>> @@ -2403,10 +2343,10 @@ static struct sk_buff *receive_mergeable_xdp(struct net_device *dev,
>>>>    		break;
>>>>    	}
>>>> -	put_xdp_frags(&xdp);
>>>> +	put_xdp_frags(rq, &xdp);
>>>>    err_xdp:
>>>> -	put_page(page);
>>>> +	virtnet_put_page(rq, page, true);
>>>>    	mergeable_buf_free(rq, num_buf, dev, stats);
>>>>    	u64_stats_inc(&stats->xdp_drops);
>>>> @@ -2414,7 +2354,8 @@ static struct sk_buff *receive_mergeable_xdp(struct net_device *dev,
>>>>    	return NULL;
>>>>    }
>>>> -static struct sk_buff *virtnet_skb_append_frag(struct sk_buff *head_skb,
>>>> +static struct sk_buff *virtnet_skb_append_frag(struct receive_queue *rq,
>>>> +					       struct sk_buff *head_skb,
>>>>    					       struct sk_buff *curr_skb,
>>>>    					       struct page *page, void *buf,
>>>>    					       int len, int truesize)
>>>> @@ -2446,7 +2387,7 @@ static struct sk_buff *virtnet_skb_append_frag(struct sk_buff *head_skb,
>>>>    	offset = buf - page_address(page);
>>>>    	if (skb_can_coalesce(curr_skb, num_skb_frags, page, offset)) {
>>>> -		put_page(page);
>>>> +		virtnet_put_page(rq, page, true);
>>>>    		skb_coalesce_rx_frag(curr_skb, num_skb_frags - 1,
>>>>    				     len, truesize);
>>>>    	} else {
>>>> @@ -2499,6 +2440,8 @@ static struct sk_buff *receive_mergeable(struct net_device *dev,
>>>>    	if (unlikely(!curr_skb))
>>>>    		goto err_skb;
>>>> +
>>>> +	skb_mark_for_recycle(head_skb);
>>>>    	while (--num_buf) {
>>>>    		buf = virtnet_rq_get_buf(rq, &len, &ctx);
>>>>    		if (unlikely(!buf)) {
>>>> @@ -2517,7 +2460,7 @@ static struct sk_buff *receive_mergeable(struct net_device *dev,
>>>>    			goto err_skb;
>>>>    		truesize = mergeable_ctx_to_truesize(ctx);
>>>> -		curr_skb  = virtnet_skb_append_frag(head_skb, curr_skb, page,
>>>> +		curr_skb  = virtnet_skb_append_frag(rq, head_skb, curr_skb, page,
>>>>    						    buf, len, truesize);
>>>>    		if (!curr_skb)
>>>>    			goto err_skb;
>>>> @@ -2527,7 +2470,7 @@ static struct sk_buff *receive_mergeable(struct net_device *dev,
>>>>    	return head_skb;
>>>>    err_skb:
>>>> -	put_page(page);
>>>> +	virtnet_put_page(rq, page, true);
>>>>    	mergeable_buf_free(rq, num_buf, dev, stats);
>>>>    err_buf:
>>>> @@ -2666,32 +2609,42 @@ static void receive_buf(struct virtnet_info *vi, struct receive_queue *rq,
>>>>    static int add_recvbuf_small(struct virtnet_info *vi, struct receive_queue *rq,
>>>>    			     gfp_t gfp)
>>>>    {
>>>> -	char *buf;
>>>>    	unsigned int xdp_headroom = virtnet_get_headroom(vi);
>>>>    	void *ctx = (void *)(unsigned long)xdp_headroom;
>>>>    	int len = vi->hdr_len + VIRTNET_RX_PAD + GOOD_PACKET_LEN + xdp_headroom;
>>>> +	unsigned int offset;
>>>> +	struct page *page;
>>>> +	dma_addr_t addr;
>>>> +	char *buf;
>>>>    	int err;
>>>>    	len = SKB_DATA_ALIGN(len) +
>>>>    	      SKB_DATA_ALIGN(sizeof(struct skb_shared_info));
>>>> -	if (unlikely(!skb_page_frag_refill(len, &rq->alloc_frag, gfp)))
>>>> -		return -ENOMEM;
>>>> -
>>>> -	buf = virtnet_rq_alloc(rq, len, gfp);
>>>> -	if (unlikely(!buf))
>>>> +	page = page_pool_alloc_frag(rq->page_pool, &offset, len, gfp);
>>>> +	if (unlikely(!page))
>>>>    		return -ENOMEM;
>>>> +	buf = page_address(page) + offset;
>>>>    	buf += VIRTNET_RX_PAD + xdp_headroom;
>>>> -	virtnet_rq_init_one_sg(rq, buf, vi->hdr_len + GOOD_PACKET_LEN);
>>>> +	if (rq->use_page_pool_dma) {
>>>> +		addr = page_pool_get_dma_addr(page) + offset;
>>>> +		addr += VIRTNET_RX_PAD + xdp_headroom;
>>>> -	err = virtqueue_add_inbuf_premapped(rq->vq, rq->sg, 1, buf, ctx, gfp);
>>>> -	if (err < 0) {
>>>> -		virtnet_rq_unmap(rq, buf, 0);
>>>> -		put_page(virt_to_head_page(buf));
>>>> +		sg_init_table(rq->sg, 1);
>>>> +		sg_fill_dma(rq->sg, addr, vi->hdr_len + GOOD_PACKET_LEN);
>>>> +		err = virtqueue_add_inbuf_premapped(rq->vq, rq->sg, 1,
>>>> +						    buf, ctx, gfp);
>>>> +	} else {
>>>> +		sg_init_one(rq->sg, buf, vi->hdr_len + GOOD_PACKET_LEN);
>>>> +		err = virtqueue_add_inbuf_ctx(rq->vq, rq->sg, 1,
>>>> +					      buf, ctx, gfp);
>>>>    	}
>>>> +	if (err < 0)
>>>> +		page_pool_put_page(rq->page_pool, virt_to_head_page(buf),
>>>> +				   -1, false);
>>>>    	return err;
>>>>    }
>>>> @@ -2764,13 +2717,15 @@ static unsigned int get_mergeable_buf_len(struct receive_queue *rq,
>>>>    static int add_recvbuf_mergeable(struct virtnet_info *vi,
>>>>    				 struct receive_queue *rq, gfp_t gfp)
>>>>    {
>>>> -	struct page_frag *alloc_frag = &rq->alloc_frag;
>>>>    	unsigned int headroom = virtnet_get_headroom(vi);
>>>>    	unsigned int tailroom = headroom ? sizeof(struct skb_shared_info) : 0;
>>>>    	unsigned int room = SKB_DATA_ALIGN(headroom + tailroom);
>>>>    	unsigned int len, hole;
>>>> -	void *ctx;
>>>> +	unsigned int offset;
>>>> +	struct page *page;
>>>> +	dma_addr_t addr;
>>>>    	char *buf;
>>>> +	void *ctx;
>>>>    	int err;
>>>>    	/* Extra tailroom is needed to satisfy XDP's assumption. This
>>>> @@ -2779,18 +2734,14 @@ static int add_recvbuf_mergeable(struct virtnet_info *vi,
>>>>    	 */
>>>>    	len = get_mergeable_buf_len(rq, &rq->mrg_avg_pkt_len, room);
>>>> -	if (unlikely(!skb_page_frag_refill(len + room, alloc_frag, gfp)))
>>>> -		return -ENOMEM;
>>>> -
>>>> -	if (!alloc_frag->offset && len + room + sizeof(struct virtnet_rq_dma) > alloc_frag->size)
>>>> -		len -= sizeof(struct virtnet_rq_dma);
>>>> -
>>>> -	buf = virtnet_rq_alloc(rq, len + room, gfp);
>>>> -	if (unlikely(!buf))
>>>> +	page = page_pool_alloc_frag(rq->page_pool, &offset, len + room, gfp);
>>>> +	if (unlikely(!page))
>>>>    		return -ENOMEM;
>>>> +	buf = page_address(page) + offset;
>>>>    	buf += headroom; /* advance address leaving hole at front of pkt */
>>>> -	hole = alloc_frag->size - alloc_frag->offset;
>>>> +
>>>> +	hole = PAGE_SIZE - (offset + len + room);
>>>>    	if (hole < len + room) {
>>>>    		/* To avoid internal fragmentation, if there is very likely not
>>>>    		 * enough space for another buffer, add the remaining space to
>>>> @@ -2800,18 +2751,27 @@ static int add_recvbuf_mergeable(struct virtnet_info *vi,
>>>>    		 */
>>>>    		if (!headroom)
>>>>    			len += hole;
>>>> -		alloc_frag->offset += hole;
>>>
>>> Hmm. All these allocations are tricky.
>>> So we used to advance offset by hole but with page pool api
>>> what advances pool->frag_offset? If nothing will not the next
>>> small allocation reuse the space and overlap the buffer?
>>
>> I tested with debug tracing and confirmed the issue triggers with
>> typical 1536-byte allocations. When len += hole extends the buffer into
>> 3072-4096, page_pool's internal frag_offset stays at 3072, so a
>> subsequent smaller allocation could overlap.
>> Since page_pool manages frag_offset internally and there's no API to
>> advance it past the hole, the fix is to remove the if (hole < len +
>> room) block entirely.
> 
> Well... but this means that fragmentation can waste memory
> which is not accounted for anywhere. Just add an API for this?

I will add a page_pool_frag_offset_add() api in v5 and send the patch.

> 
> 
>>>
>>>
>>>>    	}
>>>> -	virtnet_rq_init_one_sg(rq, buf, len);
>>>> -
>>>>    	ctx = mergeable_len_to_ctx(len + room, headroom);
>>>> -	err = virtqueue_add_inbuf_premapped(rq->vq, rq->sg, 1, buf, ctx, gfp);
>>>> -	if (err < 0) {
>>>> -		virtnet_rq_unmap(rq, buf, 0);
>>>> -		put_page(virt_to_head_page(buf));
>>>> +
>>>> +	if (rq->use_page_pool_dma) {
>>>> +		addr = page_pool_get_dma_addr(page) + offset;
>>>> +		addr += headroom;
>>>> +
>>>> +		sg_init_table(rq->sg, 1);
>>>> +		sg_fill_dma(rq->sg, addr, len);
>>>> +		err = virtqueue_add_inbuf_premapped(rq->vq, rq->sg, 1,
>>>> +						    buf, ctx, gfp);
>>>> +	} else {
>>>> +		sg_init_one(rq->sg, buf, len);
>>>> +		err = virtqueue_add_inbuf_ctx(rq->vq, rq->sg, 1,
>>>> +					      buf, ctx, gfp);
>>>>    	}
>>>> +	if (err < 0)
>>>> +		page_pool_put_page(rq->page_pool, virt_to_head_page(buf),
>>>> +				   -1, false);
>>>>    	return err;
>>>>    }
>>>> @@ -3128,7 +3088,10 @@ static int virtnet_enable_queue_pair(struct virtnet_info *vi, int qp_index)
>>>>    		return err;
>>>>    	err = xdp_rxq_info_reg_mem_model(&vi->rq[qp_index].xdp_rxq,
>>>> -					 MEM_TYPE_PAGE_SHARED, NULL);
>>>> +					 vi->rq[qp_index].page_pool ?
>>>> +						MEM_TYPE_PAGE_POOL :
>>>> +						MEM_TYPE_PAGE_SHARED,
>>>> +					 vi->rq[qp_index].page_pool);
>>>>    	if (err < 0)
>>>>    		goto err_xdp_reg_mem_model;
>>>> @@ -3168,6 +3131,81 @@ static void virtnet_update_settings(struct virtnet_info *vi)
>>>>    		vi->duplex = duplex;
>>>>    }
>>>> +static int virtnet_create_page_pools(struct virtnet_info *vi)
>>>> +{
>>>> +	int i, err;
>>>> +
>>>> +	if (!vi->mergeable_rx_bufs && vi->big_packets)
>>>> +		return 0;
>>>> +
>>>> +	for (i = 0; i < vi->max_queue_pairs; i++) {
>>>> +		struct receive_queue *rq = &vi->rq[i];
>>>> +		struct page_pool_params pp_params = { 0 };
>>>> +		struct device *dma_dev;
>>>> +
>>>> +		if (rq->page_pool)
>>>> +			continue;
>>>> +
>>>> +		if (rq->xsk_pool)
>>>> +			continue;
>>>> +
>>>> +		pp_params.order = 0;
>>>> +		pp_params.pool_size = virtqueue_get_vring_size(rq->vq);
>>>> +		pp_params.nid = dev_to_node(vi->vdev->dev.parent);
>>>> +		pp_params.netdev = vi->dev;
>>>> +		pp_params.napi = &rq->napi;
>>>> +
>>>> +		/* Check if backend supports DMA API (e.g., vhost, virtio-pci).
>>>> +		 * If so, use page_pool's DMA mapping for premapped buffers.
>>>> +		 * Otherwise (e.g., VDUSE), page_pool only handles allocation.
>>>> +		 */
>>>> +		dma_dev = virtqueue_dma_dev(rq->vq);
>>>> +		if (dma_dev) {
>>>> +			pp_params.dev = dma_dev;
>>>> +			pp_params.flags = PP_FLAG_DMA_MAP;
>>>> +			pp_params.dma_dir = DMA_FROM_DEVICE;
>>>> +			rq->use_page_pool_dma = true;
>>>> +		} else {
>>>> +			pp_params.dev = vi->vdev->dev.parent;
>>>> +			pp_params.flags = 0;
>>>> +			rq->use_page_pool_dma = false;
>>>> +		}
>>>> +
>>>> +		rq->page_pool = page_pool_create(&pp_params);
>>>> +		if (IS_ERR(rq->page_pool)) {
>>>> +			err = PTR_ERR(rq->page_pool);
>>>> +			rq->page_pool = NULL;
>>>> +			goto err_cleanup;
>>>> +		}
>>>> +	}
>>>> +	return 0;
>>>> +
>>>> +err_cleanup:
>>>> +	while (--i >= 0) {
>>>> +		struct receive_queue *rq = &vi->rq[i];
>>>> +
>>>> +		if (rq->page_pool) {
>>>> +			page_pool_destroy(rq->page_pool);
>>>> +			rq->page_pool = NULL;
>>>> +		}
>>>> +	}
>>>> +	return err;
>>>> +}
>>>> +
>>>> +static void virtnet_destroy_page_pools(struct virtnet_info *vi)
>>>> +{
>>>> +	int i;
>>>> +
>>>> +	for (i = 0; i < vi->max_queue_pairs; i++) {
>>>> +		struct receive_queue *rq = &vi->rq[i];
>>>> +
>>>> +		if (rq->page_pool) {
>>>> +			page_pool_destroy(rq->page_pool);
>>>> +			rq->page_pool = NULL;
>>>> +		}
>>>> +	}
>>>> +}
>>>> +
>>>>    static int virtnet_open(struct net_device *dev)
>>>>    {
>>>>    	struct virtnet_info *vi = netdev_priv(dev);
>>>> @@ -6441,10 +6479,8 @@ static int virtnet_find_vqs(struct virtnet_info *vi)
>>>>    		vi->rq[i].min_buf_len = mergeable_min_buf_len(vi, vi->rq[i].vq);
>>>>    		vi->sq[i].vq = vqs[txq2vq(i)];
>>>>    	}
>>>> -
>>>>    	/* run here: ret == 0. */
>>>> -
>>>>    err_find:
>>>>    	kfree(ctx);
>>>>    err_ctx:
>>>> @@ -6945,6 +6981,14 @@ static int virtnet_probe(struct virtio_device *vdev)
>>>>    			goto free;
>>>>    	}
>>>> +	/* Create page pools for receive queues.
>>>> +	 * Page pools are created at probe time so they can be used
>>>> +	 * with premapped DMA addresses throughout the device lifetime.
>>>> +	 */
>>>> +	err = virtnet_create_page_pools(vi);
>>>> +	if (err)
>>>> +		goto free_irq_moder;
>>>> +
>>>>    #ifdef CONFIG_SYSFS
>>>>    	if (vi->mergeable_rx_bufs)
>>>>    		dev->sysfs_rx_queue_group = &virtio_net_mrg_rx_group;
>>>> @@ -6958,7 +7002,7 @@ static int virtnet_probe(struct virtio_device *vdev)
>>>>    		vi->failover = net_failover_create(vi->dev);
>>>>    		if (IS_ERR(vi->failover)) {
>>>>    			err = PTR_ERR(vi->failover);
>>>> -			goto free_vqs;
>>>> +			goto free_page_pools;
>>>>    		}
>>>>    	}
>>>> @@ -7075,7 +7119,10 @@ static int virtnet_probe(struct virtio_device *vdev)
>>>>    	unregister_netdev(dev);
>>>>    free_failover:
>>>>    	net_failover_destroy(vi->failover);
>>>> -free_vqs:
>>>> +free_page_pools:
>>>> +	virtnet_destroy_page_pools(vi);
>>>> +free_irq_moder:
>>>> +	virtnet_free_irq_moder(vi);
>>>>    	virtio_reset_device(vdev);
>>>>    	free_receive_page_frags(vi);
>>>>    	virtnet_del_vqs(vi);
>>>> @@ -7104,6 +7151,8 @@ static void remove_vq_common(struct virtnet_info *vi)
>>>>    	free_receive_page_frags(vi);
>>>> +	virtnet_destroy_page_pools(vi);
>>>> +
>>>>    	virtnet_del_vqs(vi);
>>>>    }
>>>> -- 
>>>> 2.47.3
>>>
>

Re: [PATCH net-next v4 1/2] virtio_net: add page_pool support for buffer allocation

Posted by Jason Wang 3 days, 17 hours ago

On Thu, Feb 5, 2026 at 3:36 AM Vishwanath Seshagiri <vishs@meta.com> wrote:
>
> Use page_pool for RX buffer allocation in mergeable and small buffer
> modes to enable page recycling and avoid repeated page allocator calls.
> skb_mark_for_recycle() enables page reuse in the network stack.
>
> Big packets mode is unchanged because it uses page->private for linked
> list chaining of multiple pages per buffer, which conflicts with
> page_pool's internal use of page->private.
>
> Implement conditional DMA premapping using virtqueue_dma_dev():
> - When non-NULL (vhost, virtio-pci): use PP_FLAG_DMA_MAP with page_pool
>   handling DMA mapping, submit via virtqueue_add_inbuf_premapped()
> - When NULL (VDUSE, direct physical): page_pool handles allocation only,
>   submit via virtqueue_add_inbuf_ctx()
>
> This preserves the DMA premapping optimization from commit 31f3cd4e5756b
> ("virtio-net: rq submits premapped per-buffer") while adding page_pool
> support as a prerequisite for future zero-copy features (devmem TCP,
> io_uring ZCRX).
>
> Page pools are created in probe and destroyed in remove (not open/close),
> following existing driver behavior where RX buffers remain in virtqueues
> across interface state changes.
>
> Signed-off-by: Vishwanath Seshagiri <vishs@meta.com>
> ---
>  drivers/net/Kconfig      |   1 +
>  drivers/net/virtio_net.c | 351 ++++++++++++++++++++++-----------------
>  2 files changed, 201 insertions(+), 151 deletions(-)
>

Looks good overall, just one spot.

> -static void virtnet_rq_init_one_sg(struct receive_queue *rq, void *buf, u32 len)
> -{
> -       struct virtnet_info *vi = rq->vq->vdev->priv;
> -       struct virtnet_rq_dma *dma;
> -       dma_addr_t addr;
> -       u32 offset;
> -       void *head;
> -
> -       BUG_ON(vi->big_packets && !vi->mergeable_rx_bufs);
> -
> -       head = page_address(rq->alloc_frag.page);
> -
> -       offset = buf - head;
> -
> -       dma = head;
> -
> -       addr = dma->addr - sizeof(*dma) + offset;
> -
> -       sg_init_table(rq->sg, 1);
> -       sg_fill_dma(rq->sg, addr, len);
> -}
> -
> -static void *virtnet_rq_alloc(struct receive_queue *rq, u32 size, gfp_t gfp)
> -{
> -       struct page_frag *alloc_frag = &rq->alloc_frag;
> -       struct virtnet_info *vi = rq->vq->vdev->priv;
> -       struct virtnet_rq_dma *dma;
> -       void *buf, *head;
> -       dma_addr_t addr;
>
>         BUG_ON(vi->big_packets && !vi->mergeable_rx_bufs);
>
> -       head = page_address(alloc_frag->page);
> -
> -       dma = head;
> -
> -       /* new pages */
> -       if (!alloc_frag->offset) {
> -               if (rq->last_dma) {
> -                       /* Now, the new page is allocated, the last dma
> -                        * will not be used. So the dma can be unmapped
> -                        * if the ref is 0.
> -                        */
> -                       virtnet_rq_unmap(rq, rq->last_dma, 0);
> -                       rq->last_dma = NULL;
> -               }
> -
> -               dma->len = alloc_frag->size - sizeof(*dma);
> -
> -               addr = virtqueue_map_single_attrs(rq->vq, dma + 1,
> -                                                 dma->len, DMA_FROM_DEVICE, 0);
> -               if (virtqueue_map_mapping_error(rq->vq, addr))
> -                       return NULL;
> -
> -               dma->addr = addr;
> -               dma->need_sync = virtqueue_map_need_sync(rq->vq, addr);
> -
> -               /* Add a reference to dma to prevent the entire dma from
> -                * being released during error handling. This reference
> -                * will be freed after the pages are no longer used.
> -                */
> -               get_page(alloc_frag->page);
> -               dma->ref = 1;
> -               alloc_frag->offset = sizeof(*dma);
> -
> -               rq->last_dma = dma;
> -       }
> -
> -       ++dma->ref;

This patch still uses virtnet_rq_unmap() for free_receive_page_frags()
which looks like a bug.

Thanks

[PATCH net-next v4 1/2] virtio_net: add page_pool support for buffer allocation
[PATCH net-next v4 2/2] selftests: virtio_net: add buffer circulation test