From: Ming Lei <ming.lei@redhat.com>
To: Christoph Hellwig <hch@lst.de>
Cc: axboe@fb.com, Matias Bjorling <mb@lightnvm.io>,
linux-block@vger.kernel.org
Subject: Re: [PATCH 01/10] block: don't decrement nr_phys_segments for physically contigous segments
Date: Mon, 13 May 2019 17:45:45 +0800 [thread overview]
Message-ID: <20190513094544.GA30381@ming.t460p> (raw)
In-Reply-To: <20190513063754.1520-2-hch@lst.de>
On Mon, May 13, 2019 at 08:37:45AM +0200, Christoph Hellwig wrote:
> Currently ll_merge_requests_fn, unlike all other merge functions,
> reduces nr_phys_segments by one if the last segment of the previous,
> and the first segment of the next segement are contigous. While this
> seems like a nice solution to avoid building smaller than possible
Some workloads need this optimization, please see 729204ef49ec00b
("block: relax check on sg gap"):
If the last bvec of the 1st bio and the 1st bvec of the next
bio are physically contigious, and the latter can be merged
to last segment of the 1st bio, we should think they don't
violate sg gap(or virt boundary) limit.
Both Vitaly and Dexuan reported lots of unmergeable small bios
are observed when running mkfs on Hyper-V virtual storage, and
performance becomes quite low. This patch fixes that performance
issue.
It can be observed that thousands of 512byte bios in one request when
running mkfs related workloads.
> requests it causes a mismatch between the segments actually present
> in the request and those iterated over by the bvec iterators, including
> __rq_for_each_bio. This could cause overwrites of too small kmalloc
Request based drivers usually shouldn't iterate bio any more.
Thanks,
Ming
next prev parent reply other threads:[~2019-05-13 9:45 UTC|newest]
Thread overview: 27+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-05-13 6:37 fix nr_phys_segments vs iterators accounting Christoph Hellwig
2019-05-13 6:37 ` [PATCH 01/10] block: don't decrement nr_phys_segments for physically contigous segments Christoph Hellwig
2019-05-13 9:45 ` Ming Lei [this message]
2019-05-13 12:03 ` Christoph Hellwig
2019-05-13 12:37 ` Christoph Hellwig
2019-05-14 4:36 ` Ming Lei
2019-05-14 5:14 ` Christoph Hellwig
2019-05-14 9:05 ` Ming Lei
2019-05-14 13:51 ` Christoph Hellwig
2019-05-14 13:57 ` Hannes Reinecke
2019-05-14 14:27 ` Ming Lei
2019-05-14 14:31 ` Christoph Hellwig
2019-05-14 14:32 ` Christoph Hellwig
2019-05-13 6:37 ` [PATCH 02/10] block: force an unlimited segment size on queues with a virt boundary Christoph Hellwig
2019-05-15 8:19 ` Ming Lei
2019-05-13 6:37 ` [PATCH 03/10] block: remove the segment size check in bio_will_gap Christoph Hellwig
2019-05-15 8:34 ` Ming Lei
2019-05-13 6:37 ` [PATCH 04/10] block: remove the bi_seg_{front,back}_size fields in struct bio Christoph Hellwig
2019-05-13 6:37 ` [PATCH 05/10] block: initialize the write priority in blk_rq_bio_prep Christoph Hellwig
2019-05-13 7:34 ` Minwoo Im
2019-05-13 15:04 ` Chaitanya Kulkarni
2019-05-13 6:37 ` [PATCH 06/10] block: remove blk_init_request_from_bio Christoph Hellwig
2019-05-13 6:37 ` [PATCH 07/10] block: remove the bi_phys_segments field in struct bio Christoph Hellwig
2019-05-13 6:37 ` [PATCH 08/10] block: simplify blk_recalc_rq_segments Christoph Hellwig
2019-05-13 6:37 ` [PATCH 09/10] block: untangle the end of blk_bio_segment_split Christoph Hellwig
2019-05-13 6:37 ` [PATCH 10/10] block: mark blk_rq_bio_prep as inline Christoph Hellwig
2019-05-13 14:57 ` Chaitanya Kulkarni
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