Re: [PATCH 25/34] mm: vmscan: Check if reclaim should really aborteven if compaction_ready() is true for one zone

[Greg KH]

On Mon, Jul 23, 2012 at 02:38:38PM +0100, Mel Gorman wrote:
> commit 0cee34fd72c582b4f8ad8ce00645b75fb4168199 upstream.
> 
> Stable note: Not tracked on Bugzilla. THP and compaction was found to
> 	aggressively reclaim pages and stall systems under different
> 	situations that was addressed piecemeal over time.
> 
> If compaction can proceed for a given zone, shrink_zones() does not
> reclaim any more pages from it. After commit [e0c2327: vmscan: abort
> reclaim/compaction if compaction can proceed], do_try_to_free_pages()
> tries to finish as soon as possible once one zone can compact.
> 
> This was intended to prevent slabs being shrunk unnecessarily but
> there are side-effects. One is that a small zone that is ready for
> compaction will abort reclaim even if the chances of successfully
> allocating a THP from that zone is small. It also means that reclaim
> can return too early even though sc->nr_to_reclaim pages were not
> reclaimed.
> 
> This partially reverts the commit until it is proven that slabs are
> really being shrunk unnecessarily but preserves the check to return
> 1 to avoid OOM if reclaim was aborted prematurely.
> 
> [aarcange@xxxxxxxxxx: This patch replaces a revert from Andrea]
> Signed-off-by: Mel Gorman <mgorman@xxxxxxx>
> Reviewed-by: Rik van Riel <riel@xxxxxxxxxx>
> Cc: Andrea Arcangeli <aarcange@xxxxxxxxxx>
> Cc: Minchan Kim <minchan.kim@xxxxxxxxx>
> Cc: Dave Jones <davej@xxxxxxxxxx>
> Cc: Jan Kara <jack@xxxxxxx>
> Cc: Andy Isaacson <adi@xxxxxxxxxxxxx>
> Cc: Nai Xia <nai.xia@xxxxxxxxx>
> Cc: Johannes Weiner <jweiner@xxxxxxxxxx>
> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
> Signed-off-by: Mel Gorman <mgorman@xxxxxxx>
> ---
>  mm/vmscan.c |   19 +++++++++----------
>  1 file changed, 9 insertions(+), 10 deletions(-)
> 
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index f109f2d..bc31f32 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -2129,7 +2129,8 @@ static inline bool compaction_ready(struct zone *zone, struct scan_control *sc)
>   *
>   * This function returns true if a zone is being reclaimed for a costly
>   * allocation and compaction is ready to begin. This indicates to the caller
> - * that it should retry the allocation or fail.
> + * that it should consider retrying the allocation instead of
> + * further reclaim.
>   */
>  static bool shrink_zones(int priority, struct zonelist *zonelist,
>  					struct scan_control *sc)

This hunk didn't apply (the original commit from Linus's tree also
didn't apply due to some context changes in the rest of the patch.)  So
I took the original comment changes from Linus's tree, and the context
changes from this one and applied that.

Franken-patches, the story of my life...

greg k-h
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