On Mon 30-07-12 15:32:18, 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.
This is a bit misleading because there is no softlimit per zone...
> If that is the case, the current implementation will burn extra cpu
> cycles without making forward progress.
This scales with the number of groups which is bareable I guess. We do
not drop priority so the wasted round will not make a bigger pressure on
the reclaim.
> 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>
> ---
> mm/vmscan.c | 17 +++++++++++++++--
> 1 files changed, 15 insertions(+), 2 deletions(-)
>
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index 59e633c..747d903 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -1861,6 +1861,10 @@ static void shrink_zone(struct zone *zone, struct scan_control *sc)
> .priority = sc->priority,
> };
> struct mem_cgroup *memcg;
> + bool over_softlimit, ignore_softlimit = false;
> +
> +restart:
> + over_softlimit = false;
>
> memcg = mem_cgroup_iter(root, NULL, &reclaim);
> do {
> @@ -1879,10 +1883,14 @@ static void shrink_zone(struct zone *zone, struct scan_control *sc)
> * 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))
> + if (ignore_softlimit || !global_reclaim(sc) ||
> + sc->priority < DEF_PRIORITY - 2 ||
> + mem_cgroup_over_soft_limit(memcg)) {
> shrink_lruvec(lruvec, sc);
>
> + over_softlimit = true;
> + }
> +
> /*
> * Limit reclaim has historically picked one memcg and
> * scanned it with decreasing priority levels until
> @@ -1899,6 +1907,11 @@ static void shrink_zone(struct zone *zone, struct scan_control *sc)
> }
> memcg = mem_cgroup_iter(root, memcg, &reclaim);
> } while (memcg);
> +
> + if (!over_softlimit) {
Is this ever false? At least root cgroup is always above the limit.
Shouldn't we rather compare reclaimed pages?
> + ignore_softlimit = true;
> + goto restart;
> + }
> }
>
> /* Returns true if compaction should go ahead for a high-order request */
> --
> 1.7.7.3
>
--
Michal Hocko
SUSE Labs
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