From mboxrd@z Thu Jan 1 00:00:00 1970 From: akpm@linux-foundation.org Subject: [merged] bio-modify-__bio_add_page-to-accept-pages-that-dont-start-a-new-segment.patch removed from -mm tree Date: Sat, 13 Dec 2014 20:10:50 -0800 Message-ID: <548d0dca.Wv2oSdfDMTUleq0N%akpm@linux-foundation.org> Reply-To: linux-kernel@vger.kernel.org Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Return-path: Received: from mail.linuxfoundation.org ([140.211.169.12]:47978 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752526AbaLNEKm (ORCPT ); Sat, 13 Dec 2014 23:10:42 -0500 Sender: mm-commits-owner@vger.kernel.org List-Id: mm-commits@vger.kernel.org To: mlombard@redhat.com, axboe@kernel.dk, jet.chen@intel.com, ming.lei@canonical.com, thenzl@redhat.com, mm-commits@vger.kernel.org The patch titled Subject: bio: modify __bio_add_page() to accept pages that don't start a new segment has been removed from the -mm tree. Its filename was bio-modify-__bio_add_page-to-accept-pages-that-dont-start-a-new-segment.patch This patch was dropped because it was merged into mainline or a subsystem tree ------------------------------------------------------ From: Maurizio Lombardi Subject: bio: modify __bio_add_page() to accept pages that don't start a new segment The original behaviour is to refuse to add a new page if the maximum number of segments has been reached, regardless of the fact the page we are going to add can be merged into the last segment or not. Unfortunately, when the system runs under heavy memory fragmentation conditions, a driver may try to add multiple pages to the last segment. The original code won't accept them and EBUSY will be reported to userspace. This patch modifies the function so it refuses to add a page only in case the latter starts a new segment and the maximum number of segments has already been reached. The bug can be easily reproduced with the st driver: 1) set CONFIG_SCSI_MPT2SAS_MAX_SGE or CONFIG_SCSI_MPT3SAS_MAX_SGE to 16 2) modprobe st buffer_kbs=1024 3) #dd if=/dev/zero of=/dev/st0 bs=1M count=10 dd: error writing `/dev/st0': Device or resource busy Signed-off-by: Maurizio Lombardi Signed-off-by: Ming Lei Cc: Jet Chen Cc: Tomas Henzl Cc: Jens Axboe Signed-off-by: Andrew Morton --- block/bio.c | 54 +++++++++++++++++++++++++++----------------------- 1 file changed, 30 insertions(+), 24 deletions(-) diff -puN block/bio.c~bio-modify-__bio_add_page-to-accept-pages-that-dont-start-a-new-segment block/bio.c --- a/block/bio.c~bio-modify-__bio_add_page-to-accept-pages-that-dont-start-a-new-segment +++ a/block/bio.c @@ -748,6 +748,7 @@ static int __bio_add_page(struct request } } + bio->bi_iter.bi_size += len; goto done; } @@ -764,29 +765,32 @@ static int __bio_add_page(struct request return 0; /* - * we might lose a segment or two here, but rather that than - * make this too complex. + * setup the new entry, we might clear it again later if we + * cannot add the page + */ + bvec = &bio->bi_io_vec[bio->bi_vcnt]; + bvec->bv_page = page; + bvec->bv_len = len; + bvec->bv_offset = offset; + bio->bi_vcnt++; + bio->bi_phys_segments++; + bio->bi_iter.bi_size += len; + + /* + * Perform a recount if the number of segments is greater + * than queue_max_segments(q). */ - while (bio->bi_phys_segments >= queue_max_segments(q)) { + while (bio->bi_phys_segments > queue_max_segments(q)) { if (retried_segments) - return 0; + goto failed; retried_segments = 1; blk_recount_segments(q, bio); } /* - * setup the new entry, we might clear it again later if we - * cannot add the page - */ - bvec = &bio->bi_io_vec[bio->bi_vcnt]; - bvec->bv_page = page; - bvec->bv_len = len; - bvec->bv_offset = offset; - - /* * if queue has other restrictions (eg varying max sector size * depending on offset), it can specify a merge_bvec_fn in the * queue to get further control @@ -795,7 +799,7 @@ static int __bio_add_page(struct request struct bvec_merge_data bvm = { .bi_bdev = bio->bi_bdev, .bi_sector = bio->bi_iter.bi_sector, - .bi_size = bio->bi_iter.bi_size, + .bi_size = bio->bi_iter.bi_size - len, .bi_rw = bio->bi_rw, }; @@ -803,23 +807,25 @@ static int __bio_add_page(struct request * merge_bvec_fn() returns number of bytes it can accept * at this offset */ - if (q->merge_bvec_fn(q, &bvm, bvec) < bvec->bv_len) { - bvec->bv_page = NULL; - bvec->bv_len = 0; - bvec->bv_offset = 0; - return 0; - } + if (q->merge_bvec_fn(q, &bvm, bvec) < bvec->bv_len) + goto failed; } /* If we may be able to merge these biovecs, force a recount */ - if (bio->bi_vcnt && (BIOVEC_PHYS_MERGEABLE(bvec-1, bvec))) + if (bio->bi_vcnt > 1 && (BIOVEC_PHYS_MERGEABLE(bvec-1, bvec))) bio->bi_flags &= ~(1 << BIO_SEG_VALID); - bio->bi_vcnt++; - bio->bi_phys_segments++; done: - bio->bi_iter.bi_size += len; return len; + + failed: + bvec->bv_page = NULL; + bvec->bv_len = 0; + bvec->bv_offset = 0; + bio->bi_vcnt--; + bio->bi_iter.bi_size -= len; + blk_recount_segments(q, bio); + return 0; } /** _ Patches currently in -mm which might be from mlombard@redhat.com are origin.patch linux-next.patch