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Thu, 06 Nov 2025 09:17:05 -0800 (PST) X-Relaying-Domain: purestorage.com Received: from dev-csander.dev.purestorage.com (dev-csander.dev.purestorage.com [10.7.70.37]) by c7-smtp-2023.dev.purestorage.com (Postfix) with ESMTP id 9C45D340410; Thu, 6 Nov 2025 10:17:04 -0700 (MST) Received: by dev-csander.dev.purestorage.com (Postfix, from userid 1557716354) id 9817DE401BC; Thu, 6 Nov 2025 10:17:04 -0700 (MST) From: Caleb Sander Mateos To: Ming Lei , Jens Axboe Cc: linux-block@vger.kernel.org, linux-kernel@vger.kernel.org, Caleb Sander Mateos Subject: [PATCH v3 1/2] ublk: use copy_{to,from}_iter() for user copy Date: Thu, 6 Nov 2025 10:16:46 -0700 Message-ID: <20251106171647.2590074-2-csander@purestorage.com> X-Mailer: git-send-email 2.45.2 In-Reply-To: <20251106171647.2590074-1-csander@purestorage.com> References: <20251106171647.2590074-1-csander@purestorage.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 Content-Type: text/plain; charset="utf-8" ublk_copy_user_pages()/ublk_copy_io_pages() currently uses iov_iter_get_pages2() to extract the pages from the iov_iter and memcpy()s between the bvec_iter and the iov_iter's pages one at a time. Switch to using copy_to_iter()/copy_from_iter() instead. This avoids the user page reference count increments and decrements and needing to split the memcpy() at user page boundaries. It also simplifies the code considerably. Ming reports a 40% throughput improvement when issuing I/O to the selftests null ublk server with zero-copy disabled. Signed-off-by: Caleb Sander Mateos Reviewed-by: Ming Lei --- drivers/block/ublk_drv.c | 62 +++++++++------------------------------- 1 file changed, 14 insertions(+), 48 deletions(-) diff --git a/drivers/block/ublk_drv.c b/drivers/block/ublk_drv.c index 97cc4bc0a6ce..40eee3e15a4c 100644 --- a/drivers/block/ublk_drv.c +++ b/drivers/block/ublk_drv.c @@ -911,58 +911,47 @@ static const struct block_device_operations ub_fops = =3D { .open =3D ublk_open, .free_disk =3D ublk_free_disk, .report_zones =3D ublk_report_zones, }; =20 -#define UBLK_MAX_PIN_PAGES 32 - struct ublk_io_iter { - struct page *pages[UBLK_MAX_PIN_PAGES]; struct bio *bio; struct bvec_iter iter; }; =20 -/* return how many pages are copied */ -static void ublk_copy_io_pages(struct ublk_io_iter *data, - size_t total, size_t pg_off, int dir) +/* return how many bytes are copied */ +static size_t ublk_copy_io_pages(struct ublk_io_iter *data, + struct iov_iter *uiter, int dir) { - unsigned done =3D 0; - unsigned pg_idx =3D 0; + size_t done =3D 0; =20 - while (done < total) { + for (;;) { struct bio_vec bv =3D bio_iter_iovec(data->bio, data->iter); - unsigned int bytes =3D min3(bv.bv_len, (unsigned)total - done, - (unsigned)(PAGE_SIZE - pg_off)); void *bv_buf =3D bvec_kmap_local(&bv); - void *pg_buf =3D kmap_local_page(data->pages[pg_idx]); + size_t copied; =20 if (dir =3D=3D ITER_DEST) - memcpy(pg_buf + pg_off, bv_buf, bytes); + copied =3D copy_to_iter(bv_buf, bv.bv_len, uiter); else - memcpy(bv_buf, pg_buf + pg_off, bytes); + copied =3D copy_from_iter(bv_buf, bv.bv_len, uiter); =20 - kunmap_local(pg_buf); kunmap_local(bv_buf); =20 - /* advance page array */ - pg_off +=3D bytes; - if (pg_off =3D=3D PAGE_SIZE) { - pg_idx +=3D 1; - pg_off =3D 0; - } - - done +=3D bytes; + done +=3D copied; + if (copied < bv.bv_len) + break; =20 /* advance bio */ - bio_advance_iter_single(data->bio, &data->iter, bytes); + bio_advance_iter_single(data->bio, &data->iter, copied); if (!data->iter.bi_size) { data->bio =3D data->bio->bi_next; if (data->bio =3D=3D NULL) break; data->iter =3D data->bio->bi_iter; } } + return done; } =20 static bool ublk_advance_io_iter(const struct request *req, struct ublk_io_iter *iter, unsigned int offset) { @@ -986,38 +975,15 @@ static bool ublk_advance_io_iter(const struct request= *req, */ static size_t ublk_copy_user_pages(const struct request *req, unsigned offset, struct iov_iter *uiter, int dir) { struct ublk_io_iter iter; - size_t done =3D 0; =20 if (!ublk_advance_io_iter(req, &iter, offset)) return 0; =20 - while (iov_iter_count(uiter) && iter.bio) { - unsigned nr_pages; - ssize_t len; - size_t off; - int i; - - len =3D iov_iter_get_pages2(uiter, iter.pages, - iov_iter_count(uiter), - UBLK_MAX_PIN_PAGES, &off); - if (len <=3D 0) - return done; - - ublk_copy_io_pages(&iter, len, off, dir); - nr_pages =3D DIV_ROUND_UP(len + off, PAGE_SIZE); - for (i =3D 0; i < nr_pages; i++) { - if (dir =3D=3D ITER_DEST) - set_page_dirty(iter.pages[i]); - put_page(iter.pages[i]); - } - done +=3D len; - } - - return done; + return ublk_copy_io_pages(&iter, uiter, dir); } =20 static inline bool ublk_need_map_req(const struct request *req) { return ublk_rq_has_data(req) && req_op(req) =3D=3D REQ_OP_WRITE; --=20 2.45.2