On Sun, Jun 17, 2012 at 7:54 PM, Kamezawa Hiroyuki
<kamezawa.hiroyu@xxxxxxxxxxxxxx> wrote:
> (2012/06/07 3:23), Ying Han wrote:
>> In memcg kernel, cgroup under its softlimit is not targeted under global
>> reclaim. It could be possible that all memcgs are under their softlimit for
>> a particular zone. If that is the case, the current implementation will
>> burn extra cpu cycles without making forward progress.
>>
>> The idea is from LSF discussion where we detect it after the first round of
>> scanning and restart the reclaim by not looking at softlimit at all. This
>> allows us to make forward progress on shrink_zone().
>>
>> Signed-off-by: Ying Han<yinghan@xxxxxxxxxx>
>
> Hm, how about adding sc->ignore_softlimit and preserve the result among priority loops ?
>
> Is it better to check 'ignore_softlimit' at every priority updates ?
The softlimit and usage_in_bytes could change on each memcg, and we
might have to check the ignore_softlimit on each priority loop.
--Ying
>
> Thanks,
> -Kame
>
>> ---
>> mm/vmscan.c | 18 ++++++++++++++++--
>> 1 files changed, 16 insertions(+), 2 deletions(-)
>>
>> diff --git a/mm/vmscan.c b/mm/vmscan.c
>> index 0560783..5d036f5 100644
>> --- a/mm/vmscan.c
>> +++ b/mm/vmscan.c
>> @@ -2142,6 +2142,10 @@ static void shrink_zone(int priority, struct zone *zone,
>> .priority = priority,
>> };
>> struct mem_cgroup *memcg;
>> + bool over_softlimit, ignore_softlimit = false;
>> +
>> +restart:
>> + over_softlimit = false;
>>
>> memcg = mem_cgroup_iter(root, NULL,&reclaim);
>> do {
>> @@ -2163,9 +2167,14 @@ static void shrink_zone(int priority, struct zone *zone,
>> * we have to reclaim under softlimit instead of burning more
>> * cpu cycles.
>> */
>> - if (!global_reclaim(sc) || priority< DEF_PRIORITY - 2 ||
>> - should_reclaim_mem_cgroup(memcg))
>> + if (ignore_softlimit || !global_reclaim(sc) ||
>> + priority< DEF_PRIORITY - 2 ||
>> + should_reclaim_mem_cgroup(memcg)) {
>> shrink_mem_cgroup_zone(priority,&mz, sc);
>> +
>> + over_softlimit = true;
>> + }
>> +
>> /*
>> * Limit reclaim has historically picked one memcg and
>> * scanned it with decreasing priority levels until
>> @@ -2182,6 +2191,11 @@ static void shrink_zone(int priority, struct zone *zone,
>> }
>> memcg = mem_cgroup_iter(root, memcg,&reclaim);
>> } while (memcg);
>> +
>> + if (!over_softlimit) {
>> + ignore_softlimit = true;
>> + goto restart;
>> + }
>> }
>>
>> /* Returns true if compaction should go ahead for a high-order request */
>
>
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