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From: Tejun Heo <tj@kernel.org>
To: Konstantin Khlebnikov <khlebnikov@yandex-team.ru>
Cc: linux-fsdevel@vger.kernel.org, linux-mm@kvack.org,
	linux-kernel@vger.kernel.org, Jens Axboe <axboe@kernel.dk>,
	Michal Hocko <mhocko@suse.com>,
	Dave Chinner <david@fromorbit.com>, Mel Gorman <mgorman@suse.de>,
	Johannes Weiner <hannes@cmpxchg.org>,
	Linus Torvalds <torvalds@linux-foundation.org>
Subject: Re: [PATCH v2] mm: implement write-behind policy for sequential file writes
Date: Mon, 23 Sep 2019 08:19:12 -0700	[thread overview]
Message-ID: <20190923151912.GG2233839@devbig004.ftw2.facebook.com> (raw)
In-Reply-To: <ed5d930c-88c6-c8e4-4a6c-529701caa993@yandex-team.ru>

Hello,

On Mon, Sep 23, 2019 at 06:06:46PM +0300, Konstantin Khlebnikov wrote:
> On 23/09/2019 17.52, Tejun Heo wrote:
> >Hello, Konstantin.
> >
> >On Fri, Sep 20, 2019 at 10:39:33AM +0300, Konstantin Khlebnikov wrote:
> >>With vm.dirty_write_behind 1 or 2 files are written even faster and
> >
> >Is the faster speed reproducible?  I don't quite understand why this
> >would be.
> 
> Writing to disk simply starts earlier.

I see.

> >Generic write-behind would definitely have other benefits and also a
> >bunch of regression possibilities.  I'm not trying to say that
> >write-behind isn't a good idea but it'd be useful to consider that a
> >good portion of the benefits can already be obtained fairly easily.
> >
> 
> I'm afraid this could end badly if each simple task like file copying
> will require own systemd job and container with manual tuning.

At least the write window size part of it is pretty easy - the range
of acceptable values is fiarly wide - and setting up a cgroup and
running a command in it isn't that expensive.  It's not like these
need full-on containers.  That said, yes, there sure are benefits to
the kernel being able to detect and handle these conditions
automagically.

Thanks.

-- 
tejun

  reply	other threads:[~2019-09-23 15:19 UTC|newest]

Thread overview: 20+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-09-20  7:35 [PATCH v2] mm: implement write-behind policy for sequential file writes Konstantin Khlebnikov
2019-09-20  7:39 ` Konstantin Khlebnikov
2019-09-23 14:52   ` Tejun Heo
2019-09-23 15:06     ` Konstantin Khlebnikov
2019-09-23 15:19       ` Tejun Heo [this message]
2019-09-24  7:39       ` Dave Chinner
2019-09-24  9:00         ` Konstantin Khlebnikov
2019-09-25  7:18           ` Dave Chinner
2019-09-25  8:15             ` Konstantin Khlebnikov
2019-09-25 23:25               ` Dave Chinner
2019-09-25 12:54             ` Theodore Y. Ts'o
2019-09-24 19:08         ` Linus Torvalds
2019-09-25  8:00           ` Dave Chinner
2019-09-20 23:05 ` Linus Torvalds
2019-09-20 23:10   ` Linus Torvalds
2019-09-23 15:36     ` Jens Axboe
2019-09-23 16:05       ` Konstantin Khlebnikov
2019-09-24  9:29   ` Konstantin Khlebnikov
2019-09-22  7:47 ` kbuild test robot
     [not found] ` <20190923003658.GA15734@shao2-debian>
2019-09-23 19:11   ` [mm] e0e7df8d5b: will-it-scale.per_process_ops -7.3% regression Konstantin Khlebnikov

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