(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 ?
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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