Re: [PATCH] mm: vmscan: check mem cgroup over reclaimed

[Ying Han <yinghan@google.com>]

On Sun, Jan 22, 2012 at 5:55 PM, Hillf Danton <dhillf@gmail.com> wrote:
> To avoid reduction in performance of reclaimee, checking overreclaim is added
> after shrinking lru list, when pages are reclaimed from mem cgroup.
>
> If over reclaim occurs, shrinking remaining lru lists is skipped, and no more
> reclaim for reclaim/compaction.
>
> Signed-off-by: Hillf Danton <dhillf@gmail.com>
> ---
>
> --- a/mm/vmscan.c       Mon Jan 23 00:23:10 2012
> +++ b/mm/vmscan.c       Mon Jan 23 09:57:20 2012
> @@ -2086,6 +2086,7 @@ static void shrink_mem_cgroup_zone(int p
>        unsigned long nr_reclaimed, nr_scanned;
>        unsigned long nr_to_reclaim = sc->nr_to_reclaim;
>        struct blk_plug plug;
> +       bool memcg_over_reclaimed = false;
>
>  restart:
>        nr_reclaimed = 0;
> @@ -2103,6 +2104,11 @@ restart:
>
>                                nr_reclaimed += shrink_list(lru, nr_to_scan,
>                                                            mz, sc, priority);
> +
> +                               memcg_over_reclaimed = !scanning_global_lru(mz)
> +                                       && (nr_reclaimed >= nr_to_reclaim);
> +                               if (memcg_over_reclaimed)
> +                                       goto out;

Why we need the change here? Do we have number to demonstrate?


>                        }
>                }
>                /*
> @@ -2116,6 +2122,7 @@ restart:
>                if (nr_reclaimed >= nr_to_reclaim && priority < DEF_PRIORITY)
>                        break;
>        }
> +out:
>        blk_finish_plug(&plug);
>        sc->nr_reclaimed += nr_reclaimed;
>
> @@ -2127,7 +2134,8 @@ restart:
>                shrink_active_list(SWAP_CLUSTER_MAX, mz, sc, priority, 0);
>
>        /* reclaim/compaction might need reclaim to continue */
> -       if (should_continue_reclaim(mz, nr_reclaimed,
> +       if (!memcg_over_reclaimed &&
> +           should_continue_reclaim(mz, nr_reclaimed,
>                                        sc->nr_scanned - nr_scanned, sc))

This changes the existing logic. What if the nr_reclaimed is greater
than nr_to_reclaim, but smaller than pages_for_compaction? The
existing logic is to continue reclaiming.

--Ying

>                goto restart;

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