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

> On Thu, May 12, 2011 at 8:03 PM, KAMEZAWA Hiroyuki <
> kamezawa.hiroyu@jp.fujitsu.com> wrote:
>
> > On Thu, 12 May 2011 17:17:25 +0900
> > KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> wrote:
> >
> > > On Thu, 12 May 2011 13:22:37 +0900
> > > KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> 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 result...in 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.

Thanks,
-Kame








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