From nobody Mon Nov 25 12:20:06 2024 Received: from szxga04-in.huawei.com (szxga04-in.huawei.com [45.249.212.190]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id E8E9A1D95A3; Mon, 28 Oct 2024 12:00:15 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=45.249.212.190 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1730116820; cv=none; b=Rzvfs8Jt8+cauy93mZKlYMbpmC7gQqbV3ihG2XsuvY2Om5etzoLYACfIjLOSVeMRKg77+CVBv9Dxbwh5iQ3x7DYDKguEdTI3e1fhFlPJRpbMIdRXwQCLtsCCz+kuJmwvCKUZdX2Av71XK8NDwDtJn+9tHsOGkZbZjKvBeeUeswo= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1730116820; c=relaxed/simple; bh=/Ogf/z0JTRia4FafOhGcEh4Ret7JEdI6NjcRq/bxgYI=; h=From:To:CC:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version:Content-Type; b=YDFp6ScRRhcU+CF7B6OG36FSnbAdCgP2UzIppyPhs9aJh6GTj1ei3CynGM5vLh1DNyRAaxw+LV8sci/NOCWcSZG4UYcC2ezCAz9PlajaBeO+XuYupTg+ArVc4xJIDI4zOWHv/rW5j4EOdUsrwZRHhhUgpaKu1o0PJxc94Xe1vw0= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=huawei.com; spf=pass smtp.mailfrom=huawei.com; arc=none smtp.client-ip=45.249.212.190 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=huawei.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=huawei.com Received: from mail.maildlp.com (unknown [172.19.88.234]) by szxga04-in.huawei.com (SkyGuard) with ESMTP id 4XcX413cz8z20r0s; Mon, 28 Oct 2024 19:59:13 +0800 (CST) Received: from dggpemf200006.china.huawei.com (unknown [7.185.36.61]) by mail.maildlp.com (Postfix) with ESMTPS id B1EDB14010C; Mon, 28 Oct 2024 20:00:10 +0800 (CST) Received: from localhost.localdomain (10.90.30.45) by dggpemf200006.china.huawei.com (7.185.36.61) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.2.1544.11; Mon, 28 Oct 2024 20:00:10 +0800 From: Yunsheng Lin To: , , CC: , , Yunsheng Lin , Alexander Duyck , Andrew Morton , Linux-MM , Alexander Duyck Subject: [PATCH net-next v23 3/7] mm: page_frag: use initial zero offset for page_frag_alloc_align() Date: Mon, 28 Oct 2024 19:53:38 +0800 Message-ID: <20241028115343.3405838-4-linyunsheng@huawei.com> X-Mailer: git-send-email 2.30.0 In-Reply-To: <20241028115343.3405838-1-linyunsheng@huawei.com> References: <20241028115343.3405838-1-linyunsheng@huawei.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable X-ClientProxiedBy: dggems705-chm.china.huawei.com (10.3.19.182) To dggpemf200006.china.huawei.com (7.185.36.61) Content-Type: text/plain; charset="utf-8" We are about to use page_frag_alloc_*() API to not just allocate memory for skb->data, but also use them to do the memory allocation for skb frag too. Currently the implementation of page_frag in mm subsystem is running the offset as a countdown rather than count-up value, there may have several advantages to that as mentioned in [1], but it may have some disadvantages, for example, it may disable skb frag coalescing and more correct cache prefetching We have a trade-off to make in order to have a unified implementation and API for page_frag, so use a initial zero offset in this patch, and the following patch will try to make some optimization to avoid the disadvantages as much as possible. 1. https://lore.kernel.org/all/f4abe71b3439b39d17a6fb2d410180f367cadf5c.cam= el@gmail.com/ CC: Alexander Duyck CC: Andrew Morton CC: Linux-MM Signed-off-by: Yunsheng Lin Reviewed-by: Alexander Duyck --- mm/page_frag_cache.c | 46 ++++++++++++++++++++++---------------------- 1 file changed, 23 insertions(+), 23 deletions(-) diff --git a/mm/page_frag_cache.c b/mm/page_frag_cache.c index 609a485cd02a..4c8e04379cb3 100644 --- a/mm/page_frag_cache.c +++ b/mm/page_frag_cache.c @@ -63,9 +63,13 @@ void *__page_frag_alloc_align(struct page_frag_cache *nc, unsigned int fragsz, gfp_t gfp_mask, unsigned int align_mask) { +#if (PAGE_SIZE < PAGE_FRAG_CACHE_MAX_SIZE) + unsigned int size =3D nc->size; +#else unsigned int size =3D PAGE_SIZE; +#endif + unsigned int offset; struct page *page; - int offset; =20 if (unlikely(!nc->va)) { refill: @@ -85,11 +89,24 @@ void *__page_frag_alloc_align(struct page_frag_cache *n= c, /* reset page count bias and offset to start of new frag */ nc->pfmemalloc =3D page_is_pfmemalloc(page); nc->pagecnt_bias =3D PAGE_FRAG_CACHE_MAX_SIZE + 1; - nc->offset =3D size; + nc->offset =3D 0; } =20 - offset =3D nc->offset - fragsz; - if (unlikely(offset < 0)) { + offset =3D __ALIGN_KERNEL_MASK(nc->offset, ~align_mask); + if (unlikely(offset + fragsz > size)) { + if (unlikely(fragsz > PAGE_SIZE)) { + /* + * The caller is trying to allocate a fragment + * with fragsz > PAGE_SIZE but the cache isn't big + * enough to satisfy the request, this may + * happen in low memory conditions. + * We don't release the cache page because + * it could make memory pressure worse + * so we simply return NULL here. + */ + return NULL; + } + page =3D virt_to_page(nc->va); =20 if (!page_ref_sub_and_test(page, nc->pagecnt_bias)) @@ -100,33 +117,16 @@ void *__page_frag_alloc_align(struct page_frag_cache = *nc, goto refill; } =20 -#if (PAGE_SIZE < PAGE_FRAG_CACHE_MAX_SIZE) - /* if size can vary use size else just use PAGE_SIZE */ - size =3D nc->size; -#endif /* OK, page count is 0, we can safely set it */ set_page_count(page, PAGE_FRAG_CACHE_MAX_SIZE + 1); =20 /* reset page count bias and offset to start of new frag */ nc->pagecnt_bias =3D PAGE_FRAG_CACHE_MAX_SIZE + 1; - offset =3D size - fragsz; - if (unlikely(offset < 0)) { - /* - * The caller is trying to allocate a fragment - * with fragsz > PAGE_SIZE but the cache isn't big - * enough to satisfy the request, this may - * happen in low memory conditions. - * We don't release the cache page because - * it could make memory pressure worse - * so we simply return NULL here. - */ - return NULL; - } + offset =3D 0; } =20 nc->pagecnt_bias--; - offset &=3D align_mask; - nc->offset =3D offset; + nc->offset =3D offset + fragsz; =20 return nc->va + offset; } --=20 2.33.0