From: Konstantin Khlebnikov <khlebnikov@yandex-team.ru>
To: Tejun Heo <tj@kernel.org>
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 18:06:46 +0300 [thread overview]
Message-ID: <ed5d930c-88c6-c8e4-4a6c-529701caa993@yandex-team.ru> (raw)
In-Reply-To: <20190923145242.GF2233839@devbig004.ftw2.facebook.com>
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.
>
>> during copying amount of dirty memory always stays around at 16MiB.
>
> The following is the test part of a slightly modified version of your
> test script which should run fine on any modern systems.
>
> for mode in 0 1; do
> if [ $mode == 0 ]; then
> prefix=''
> else
> prefix='systemd-run --user --scope -p MemoryMax=64M'
> fi
>
> echo COPY
> time $prefix cp -r dummy copy
>
> grep Dirty /proc/meminfo
>
> echo SYNC
> time sync
>
> rm -fr copy
> done
>
> and the result looks like the following.
>
> $ ./test-writebehind.sh
> SIZE
> 3.3G dummy
> COPY
>
> real 0m2.859s
> user 0m0.015s
> sys 0m2.843s
> Dirty: 3416780 kB
> SYNC
>
> real 0m34.008s
> user 0m0.000s
> sys 0m0.008s
> COPY
> Running scope as unit: run-r69dca5326a9a435d80e036435ff9e1da.scope
>
> real 0m32.267s
> user 0m0.032s
> sys 0m4.186s
> Dirty: 14304 kB
> SYNC
>
> real 0m1.783s
> user 0m0.000s
> sys 0m0.006s
>
> This is how we are solving the massive dirtier problem. It's easy,
> works pretty well and can easily be tailored to the specific
> requirements.
>
> 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.
next prev parent reply other threads:[~2019-09-23 15:06 UTC|newest]
Thread overview: 21+ 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 [this message]
2019-09-23 15:19 ` Tejun Heo
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
2019-09-23 0:36 ` [mm] e0e7df8d5b: will-it-scale.per_process_ops -7.3% regression kernel test robot
2019-09-23 19:11 ` Konstantin Khlebnikov
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