Re: [PATCH V7 1/2] mm: memcg softlimit reclaim rework

[Ying Han <yinghan@google.com>]

On Tue, Jul 31, 2012 at 8:35 AM, Michal Hocko <mhocko@suse.cz> wrote:
> Sprry for my long silence in the last rounds. I was following
> discussions but didn't get to step in.

Thank you for stepping in this round :)
>
> On Mon 30-07-12 15:32:13, Ying Han wrote:
>> This patch reverts all the existing softlimit reclaim implementations and
>> instead integrates the softlimit reclaim into existing global reclaim logic.
>>
>> The new softlimit reclaim includes the following changes:
>
> The patch seems to be doing too many things but I do not want to get
> into "split it this way or that way" now. It is probably better to have
> it like this for now and take care about these details later.

It was split and then being suggested to put together.

>
> [...]
>> 3. forbid setting soft limit on root cgroup
>>
>> Setting a soft limit in the root cgroup does not make sense, as soft limits are
>> enforced hierarchically and the root cgroup is the hierarchical parent of every
>> other cgroup.  It would not provide the discrimination between groups that soft
>> limits are usually used for.
>>
>> With the current implementation of soft limits, it would only make global reclaim
>> more aggressive compared to target reclaim, but we absolutely don't want anyone
>> to rely on this behaviour.
>
> Hmm, maybe this one can go in sooner without the rest.

Well, I have no problem to split this out if that works for ppl.

>
> [...]
>> diff --git a/mm/vmscan.c b/mm/vmscan.c
>> index 3e0d0cd..59e633c 100644
>> --- a/mm/vmscan.c
>> +++ b/mm/vmscan.c
>> @@ -1866,7 +1866,22 @@ static void shrink_zone(struct zone *zone, struct scan_control *sc)
>>       do {
>>               struct lruvec *lruvec = mem_cgroup_zone_lruvec(zone, memcg);
>>
>> -             shrink_lruvec(lruvec, sc);
>> +             /*
>> +              * Reclaim from mem_cgroup if any of these conditions are met:
>> +              * - this is a targetted reclaim ( not global reclaim)
>> +              * - reclaim priority is less than  DEF_PRIORITY - 2
>> +              * - mem_cgroup or its ancestor ( not including root cgroup)
>> +              * exceeds its soft limit
>> +              *
>> +              * Note: The priority check is a balance of how hard to
>> +              * preserve the pages under softlimit. If the memcgs of the
>> +              * zone having trouble to reclaim pages above their softlimit,
>> +              * we have to reclaim under softlimit instead of burning more
>> +              * cpu cycles.
>> +              */
>> +             if (!global_reclaim(sc) || sc->priority < DEF_PRIORITY - 2 ||
>> +                             mem_cgroup_over_soft_limit(memcg))
>> +                     shrink_lruvec(lruvec, sc);
>>
>>               /*
>>                * Limit reclaim has historically picked one memcg and
> [...]
>
> Looks quite straightforward. I have to think about it some more but I
> like it for starter. Do you have any test results from the overcommitted
> system?

I ran some tests while over-commiting the soft limit and triggering
global reclaim. Let me post the result here.

--Ying
> --
> Michal Hocko
> SUSE Labs

--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@kvack.org.  For more info on Linux MM,
see: http://www.linux-mm.org/ .
Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>