Re: [PATCH 1/7] memcg: add high/low watermark to res_counter

[Ying Han <yinghan@google.com>]

On Mon, May 9, 2011 at 4:49 PM, KAMEZAWA Hiroyuki
<kamezawa.hiroyu@jp.fujitsu.com> wrote:
> On Mon, 9 May 2011 14:49:17 +0200
> Michal Hocko <mhocko@suse.cz> wrote:
>
>> On Mon 09-05-11 12:18:17, Johannes Weiner wrote:
>> > On Mon, May 09, 2011 at 04:10:47PM +0900, KAMEZAWA Hiroyuki wrote:
>> [...]
>> > What I am wondering, though: we already have a limit to push back
>> > memcgs when we need memory, the soft limit.  The 'need for memory' is
>> > currently defined as global memory pressure, which we know may be too
>> > late.  The problem is not having no limit, the problem is that we want
>> > to control the time of when this limit is enforced.  So instead of
>> > adding another limit, could we instead add a knob like
>> >
>> >     memory.force_async_soft_reclaim
>> >
>> > that asynchroneously pushes back to the soft limit instead of having
>> > another, separate limit to configure?
>>
>
> Hmm, ok to me.

I don't have problem of the actual tunable for this, but I don't think
setting the soft_limit as the target for per-memcg background reclaim
is feasible in some cases. That will be too aggressive than it is necessary.

>
>> Sound much better than a separate watermark to me. I am just wondering
>> how we would implement soft unlimited groups with background reclaim.
>> Btw. is anybody relying on such configuration? To me it sounds like
>> something should be either limited or unlimited and making it half of
>> both is hacky.
>
> I don't think of soft-unlimited configuration. I don't want to handle it
> in some automatic way.
>
> Anyway, I'll add
>  - _automatic_ background reclaim against the limit of memory, which works
>    regarless of softlimit.

I agree to have the background reclaim first w/ automatic watermark
setting and then adding a configurable knob on top of that. So I
assume we keep the same concept of high/low_wmarks, and what's the
suggested default value for the watermarks? The default value now is
equal to hard_limit which disables he per-memcg background reclaim.
Under the new scheme which we remove the configurable tunable, we need
to set it internally based on the hard_limit.

--Ying

>  - An interface for force softlimit.
>
> Thanks,
> -Kame
>
>

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