On Thu, Nov 15, 2018 at 04:53:04PM +0800, Ming Lei wrote: > It is wrong to use bio->bi_vcnt to figure out how many segments > there are in the bio even though CLONED flag isn't set on this bio, > because this bio may be splitted or advanced. > > So always use bio_segments() in blk_recount_segments(), and it shouldn't > cause any performance loss now because the physical segment number is figured > out in blk_queue_split() and BIO_SEG_VALID is set meantime since > bdced438acd83ad83a6c ("block: setup bi_phys_segments after splitting"). > > Cc: Dave Chinner <dchin...@redhat.com> > Cc: Kent Overstreet <kent.overstr...@gmail.com> > Fixes: 7f60dcaaf91 ("block: blk-merge: fix blk_recount_segments()")
>From what I can tell, the problem was originally introduced by 76d8137a3113 ("blk-merge: recaculate segment if it isn't less than max segments") Is that right? > Cc: Mike Snitzer <snit...@redhat.com> > Cc: dm-de...@redhat.com > Cc: Alexander Viro <v...@zeniv.linux.org.uk> > Cc: linux-fsde...@vger.kernel.org > Cc: Shaohua Li <s...@kernel.org> > Cc: linux-r...@vger.kernel.org > Cc: linux-er...@lists.ozlabs.org > Cc: David Sterba <dste...@suse.com> > Cc: linux-bt...@vger.kernel.org > Cc: Darrick J. Wong <darrick.w...@oracle.com> > Cc: linux-...@vger.kernel.org > Cc: Gao Xiang <gaoxian...@huawei.com> > Cc: Christoph Hellwig <h...@lst.de> > Cc: Theodore Ts'o <ty...@mit.edu> > Cc: linux-e...@vger.kernel.org > Cc: Coly Li <col...@suse.de> > Cc: linux-bca...@vger.kernel.org > Cc: Boaz Harrosh <o...@electrozaur.com> > Cc: Bob Peterson <rpete...@redhat.com> > Cc: cluster-devel@redhat.com > Signed-off-by: Ming Lei <ming....@redhat.com> > --- > block/blk-merge.c | 8 +------- > 1 file changed, 1 insertion(+), 7 deletions(-) > > diff --git a/block/blk-merge.c b/block/blk-merge.c > index cb9f49bcfd36..153a659fde74 100644 > --- a/block/blk-merge.c > +++ b/block/blk-merge.c > @@ -429,13 +429,7 @@ void blk_recalc_rq_segments(struct request *rq) > > void blk_recount_segments(struct request_queue *q, struct bio *bio) > { > - unsigned short seg_cnt; > - > - /* estimate segment number by bi_vcnt for non-cloned bio */ > - if (bio_flagged(bio, BIO_CLONED)) > - seg_cnt = bio_segments(bio); > - else > - seg_cnt = bio->bi_vcnt; > + unsigned short seg_cnt = bio_segments(bio); > > if (test_bit(QUEUE_FLAG_NO_SG_MERGE, &q->queue_flags) && > (seg_cnt < queue_max_segments(q))) > -- > 2.9.5 >