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SubjectRe: [PATCH] mm: vmscan: check mem cgroup over reclaimed
On Mon, Jan 23, 2012 at 09:55:07AM +0800, Hillf Danton 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;

Since this merge window, scanning_global_lru() is always false when
the memory controller is enabled, i.e. most common configurations and
distribution kernels.

This will with quite likely have bad effects on zone balancing,
pressure balancing between anon/file lru etc, while you haven't shown
that any workloads actually benefit from this.

Submitting patches like this without mentioning a problematic scenario
and numbers that demonstrate that the patch improve it is not helpful.


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