linux-kernel - Re: [PATCH v2] dm: optimize flushes

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Message-ID: <96148bb3-42e3-a5e2-63fb-ad7f67ba4fea@redhat.com>
Date: Tue, 28 May 2024 13:37:53 +0200 (CEST)
From: Mikulas Patocka <mpatocka@...hat.com>
To: Mike Snitzer <snitzer@...nel.org>
cc: Benjamin Marzinski <bmarzins@...hat.com>, Yang Yang <yang.yang@...o.com>, 
    Alasdair Kergon <agk@...hat.com>, dm-devel@...ts.linux.dev, 
    linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] dm: optimize flushes



On Thu, 23 May 2024, Mike Snitzer wrote:

> On Thu, May 23, 2024 at 07:46:25PM +0200, Mikulas Patocka wrote:
> > Hi
> > 
> > Here I'm resending the patch, with more comments and explanations added.
> > 
> > Mikulas
> > 
> > 
> > From: Mikulas Patocka <mpatocka@...hat.com>
> > 
> > Device mapper sends flush bios to all the targets and the targets send it
> > to the underlying device. That may be inefficient, for example if a table
> > contains 10 linear targets pointing to the same physical device, then
> > device mapper would send 10 flush bios to that device - despite the fact
> > that only one bio would be sufficient.
> > 
> > This commit optimizes the flush behavior. It introduces a per-target
> > variable flush_bypasses_map - it is set when the target supports flush
> > optimization - currently, the dm-linear and dm-stripe targets support it.
> > When all the targets in a table have flush_bypasses_map,
> > flush_bypasses_map on the table is set. __send_empty_flush tests if the
> > table has flush_bypasses_map - and if it has, no flush bios are sent to
> > the targets via the "map" method and the list dm_table->devices is
> > iterated and the flush bios are sent to each member of the list.
> > 
> > Signed-off-by: Mikulas Patocka <mpatocka@...hat.com>
> > Suggested-by: Yang Yang <yang.yang@...o.com>
> 
> Nicely done, please feel free to stage for 6.11 (create a new
> 'dm-6.11' branch starting from 'dm-6.10' -- we'll need to rebase
> dm-6.11 to 6.10-rc2 or so but at least we'll get this commit in the
> pipeline, push to 'for-next').
> 
> Reviewed-by: Mike Snitzer <snitzer@...nel.org>

OK, done.

Mikulas