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    SubjectRe: [RFC][PATCH 0/7] memcg async reclaim
    On Thu, 12 May 2011 22:10:30 -0700
    Ying Han <> wrote:

    > On Thu, May 12, 2011 at 8:03 PM, KAMEZAWA Hiroyuki <
    >> wrote:
    > > On Thu, 12 May 2011 17:17:25 +0900
    > > KAMEZAWA Hiroyuki <> wrote:
    > >
    > > > On Thu, 12 May 2011 13:22:37 +0900
    > > > KAMEZAWA Hiroyuki <> wrote:
    > > > I'll check what codes in vmscan.c or /mm affects memcg and post a
    > > > required fix in step by step. I think I found some..
    > > >
    > >
    > > After some tests, I doubt that 'automatic' one is unnecessary until
    > > memcg's dirty_ratio is supported. And as Andrew pointed out,
    > > total cpu consumption is unchanged and I don't have workloads which
    > > shows me meaningful speed up.
    > >
    > The total cpu consumption is one way to measure the background reclaim,
    > another thing I would like to measure is a histogram of page fault latency
    > for a heavy page allocation application. I would expect with background
    > reclaim, we will get less variation on the page fault latency than w/o it.
    > Sorry i haven't got chance to run some tests to back it up. I will try to
    > get some data.

    My posted set needs some tweaks and fixes. I'll post re-tuned one in the
    next week. (But I'll be busy until Wednesday.)

    > > But I guess...with dirty_ratio, amount of dirty pages in memcg is
    > > limited and background reclaim can work enough without noise of
    > > write_page() while applications are throttled by dirty_ratio.
    > >
    > Definitely. I have run into the issue while debugging the soft_limit
    > reclaim. The background reclaim became very inefficient if we have dirty
    > pages greater than the soft_limit. Talking w/ Greg about it regarding his
    > per-memcg dirty page limit effort, we should consider setting the dirty
    > ratio which not allowing the dirty pages greater the reclaim watermarks
    > (here is the soft_limit).

    I think I got some positive some situation.

    On 8cpu, 24GB RAM system, under 300MB memcg, run 2 programs
    Program 1) while true; do cat ./test/1G > /dev/null;done
    This fills memcg with clean file cache.
    Program 2) malloc(200MB) and page-fault, free it in 200 times.

    And measure Program2's time.

    Case 1) running only Program2

    real 0m17.086s
    user 0m0.057s
    sys 0m17.257s

    Case 2) running Program 1 and 2 without async reclaim.

    [kamezawa@bluextal test]$ time ./catch_and_release > /dev/null

    real 0m26.182s
    user 0m0.115s
    sys 0m19.075s
    [kamezawa@bluextal test]$ time ./catch_and_release > /dev/null

    real 0m23.155s
    user 0m0.096s
    sys 0m18.175s
    [kamezawa@bluextal test]$ time ./catch_and_release > /dev/null

    real 0m24.667s
    user 0m0.108s
    sys 0m18.804s

    Case 3) running Program 1 and 2 with async reclaim of 8MB to limit.

    [kamezawa@bluextal test]$ time ./catch_and_release > /dev/null

    real 0m21.438s
    user 0m0.083s
    sys 0m17.864s
    [kamezawa@bluextal test]$ time ./catch_and_release > /dev/null

    real 0m23.010s
    user 0m0.079s
    sys 0m17.819s
    [kamezawa@bluextal test]$ time ./catch_and_release > /dev/null

    real 0m19.596s
    user 0m0.108s
    sys 0m18.053s

    If my test is correct, there are some meaningful positive effect.
    But I doubt there may be case with negative result case.

    I wonder to see posivie value, application shouldn't do 'write' ;)
    Anyway, I'll make a try in the next week, again.


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