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From: Christoph Hellwig <hch@lst.de>
To: Ming Lei <ming.lei@redhat.com>
Cc: Christoph Hellwig <hch@lst.de>,
	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 14:37:08 +0200	[thread overview]
Message-ID: <20190513123708.GA23671@lst.de> (raw)
In-Reply-To: <20190513120344.GA22993@lst.de>

On Mon, May 13, 2019 at 02:03:44PM +0200, Christoph Hellwig wrote:
> On Mon, May 13, 2019 at 05:45:45PM +0800, Ming Lei wrote:
> > 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"):
> 
> And we still allow to merge the segments with this patch.  The only
> difference is that these merges do get accounted as extra segments.

Trying mkfs.xfs there were no merges at all, which is expected as
it does perfectly sized direct I/O.

Trying mkfs.ext4 I see lots of bio merges.  But for those this patch
nothing changes at all, as we never decrement nr_phys_segments to start
with, we only every did that for request merges, and for those also
only for those on non-gappy devices due to the way the
req_gap_back_merge check was placed.

  reply	other threads:[~2019-05-13 12:37 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
2019-05-13 12:03     ` Christoph Hellwig
2019-05-13 12:37       ` Christoph Hellwig [this message]
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 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
     [not found] ` <CGME20190513063855epcas5p33ef8c4c0a0055bd0b66eadc859796f0f@epcms2p6>
2019-05-13  7:34   ` [PATCH 05/10] block: initialize the write priority in blk_rq_bio_prep Minwoo Im

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