Re: [PATCH] Revert "mm: vmscan: fix misused nr_reclaimed in shrink_mem_cgroup_zone()"

[Hillf Danton <dhillf@gmail.com>]

On Tue, Apr 10, 2012 at 3:42 AM, Ying Han <yinghan@google.com> wrote:
> This reverts commit c38446cc65e1f2b3eb8630c53943b94c4f65f670.
>
> Before the commit, the code makes senses to me but not after the commit. The
> "nr_reclaimed" is the number of pages reclaimed by scanning through the memcg's
> lru lists. The "nr_to_reclaim" is the target value for the whole function. For
> example, we like to early break the reclaim if reclaimed 32 pages under direct
> reclaim (not DEF_PRIORITY).
>
> After the reverted commit, the target "nr_to_reclaim" is decremented each time
> by "nr_reclaimed" but we still use it to compare the "nr_reclaimed". It just
> doesn't make sense to me...
>
I downloaded mm/vmscan.c from the next tree a couple minutes ago, and
see
		.nr_to_reclaim = SWAP_CLUSTER_MAX,
and
	nr_reclaimed = do_try_to_free_pages(zonelist, &sc, &shrink);

in try_to_free_pages().

I also see
		total_scanned += sc->nr_scanned;
		if (sc->nr_reclaimed >= sc->nr_to_reclaim)
			goto out;

in do_try_to_free_pages(),

then would you please say a few words about the sense
of the check of nr_to_reclaim?


> Signed-off-by: Ying Han <yinghan@google.com>
> ---
>  mm/vmscan.c |    7 +------
>  1 files changed, 1 insertions(+), 6 deletions(-)
>
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index 33c332b..1a51868 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -2107,12 +2107,7 @@ restart:
>                 * with multiple processes reclaiming pages, the total
>                 * freeing target can get unreasonably large.
>                 */
> -               if (nr_reclaimed >= nr_to_reclaim)
> -                       nr_to_reclaim = 0;
> -               else
> -                       nr_to_reclaim -= nr_reclaimed;
> -
> -               if (!nr_to_reclaim && priority < DEF_PRIORITY)
> +               if (nr_reclaimed >= nr_to_reclaim && priority < DEF_PRIORITY)
>                        break;
>        }
>        blk_finish_plug(&plug);
> --
> 1.7.7.3
>

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