On Tue, Jul 31, 2012 at 8:35 AM, Michal Hocko <mhocko@xxxxxxx> 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
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