Re: [PATCH 0/7] memcg background reclaim , yet another one.

[Ying Han <yinghan@google.com>]

On Tue, Apr 26, 2011 at 1:47 AM, KAMEZAWA Hiroyuki
<kamezawa.hiroyu@jp.fujitsu.com> wrote:
> On Tue, 26 Apr 2011 01:43:17 -0700
> Ying Han <yinghan@google.com> wrote:
>
>> On Tue, Apr 26, 2011 at 12:43 AM, KAMEZAWA Hiroyuki <
>> kamezawa.hiroyu@jp.fujitsu.com> wrote:
>>
>> > On Tue, 26 Apr 2011 00:19:46 -0700
>> > Ying Han <yinghan@google.com> wrote:
>> >
>> > > On Mon, Apr 25, 2011 at 6:38 PM, KAMEZAWA Hiroyuki
>> > > <kamezawa.hiroyu@jp.fujitsu.com> wrote:
>> > > > On Mon, 25 Apr 2011 15:21:21 -0700
>> > > > Ying Han <yinghan@google.com> wrote:
>
>>
>> > To clarify a bit, my question was meant to account it but not necessary to
>> > limit it. We can use existing cpu cgroup to do the cpu limiting, and I am
>> >
>> just wondering how to configure it for the memcg kswapd thread.
>>
>>    Let's say in the per-memcg-kswapd model, i can echo the kswapd thread pid
>> into the cpu cgroup ( the same set of process of memcg, but in a cpu
>> limiting cgroup instead).  If the kswapd is shared, we might need extra work
>> to account the cpu cycles correspondingly.
>>
>
> Hm ? statistics of elapsed_time isn't enough ?
>
> Now, I think limiting scan/sec interface is more promissing rather than time
> or thread controls. It's easier to understand.

I think it will work on the cpu accounting by recording the
elapsed_time per memcg workitem.

But, we might still need the cpu throttling as well. To give one use
cases from google, we'd rather kill a low priority job for running
tight on memory rather than having its reclaim thread affecting the
latency of high priority job. It is quite easy to understand how to
accomplish that in per-memcg-per-kswapd model, but harder in the
shared workqueue model. It is straight-forward to read  the cpu usage
by the cpuacct.usage* and limit the cpu usage by setting cpu.shares.
One concern we have here is the scan/sec implementation will make
things quite complex.

--Ying

>
> BTW, I think it's better to avoid the watermark reclaim work as kswapd.
> It's confusing because we've talked about global reclaim at LSF.
>
>
> Thanks,
> -Kame
>
>

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