>
> From: Michal Hocko <mhocko@xxxxxxxx>
>
> try_to_compact_pages can currently return COMPACT_SKIPPED even when the
> compaction is defered for some zone just because zone DMA is skipped
> in 99% of cases due to watermark checks. This makes COMPACT_DEFERRED
> basically unusable for the page allocator as a feedback mechanism.
>
> Make sure we distinguish those two states properly and switch their
> ordering in the enum. This would mean that the COMPACT_SKIPPED will be
> returned only when all eligible zones are skipped.
>
> As a result COMPACT_DEFERRED handling for THP in __alloc_pages_slowpath
> will be more precise and we would bail out rather than reclaim.
>
> Acked-by: Vlastimil Babka <vbabka@xxxxxxx>
> Signed-off-by: Michal Hocko <mhocko@xxxxxxxx>
> ---
Acked-by: Hillf Danton <hillf.zj@xxxxxxxxxxxxxxx>
> include/linux/compaction.h | 7 +++++--
> include/trace/events/compaction.h | 2 +-
> mm/compaction.c | 8 +++++---
> 3 files changed, 11 insertions(+), 6 deletions(-)
>
> diff --git a/include/linux/compaction.h b/include/linux/compaction.h
> index 4458fd94170f..7e177d111c39 100644
> --- a/include/linux/compaction.h
> +++ b/include/linux/compaction.h
> @@ -4,13 +4,16 @@
> /* Return values for compact_zone() and try_to_compact_pages() */
> /* When adding new states, please adjust include/trace/events/compaction.h */
> enum compact_result {
> - /* compaction didn't start as it was deferred due to past failures */
> - COMPACT_DEFERRED,
> /*
> * compaction didn't start as it was not possible or direct reclaim
> * was more suitable
> */
> COMPACT_SKIPPED,
> + /* compaction didn't start as it was deferred due to past failures */
> + COMPACT_DEFERRED,
> + /* compaction not active last round */
> + COMPACT_INACTIVE = COMPACT_DEFERRED,
> +
> /* compaction should continue to another pageblock */
> COMPACT_CONTINUE,
> /*
> diff --git a/include/trace/events/compaction.h b/include/trace/events/compaction.h
> index e215bf68f521..6ba16c86d7db 100644
> --- a/include/trace/events/compaction.h
> +++ b/include/trace/events/compaction.h
> @@ -10,8 +10,8 @@
> #include <trace/events/mmflags.h>
>
> #define COMPACTION_STATUS \
> - EM( COMPACT_DEFERRED, "deferred") \
> EM( COMPACT_SKIPPED, "skipped") \
> + EM( COMPACT_DEFERRED, "deferred") \
> EM( COMPACT_CONTINUE, "continue") \
> EM( COMPACT_PARTIAL, "partial") \
> EM( COMPACT_COMPLETE, "complete") \
> diff --git a/mm/compaction.c b/mm/compaction.c
> index b06de27b7f72..13709e33a2fc 100644
> --- a/mm/compaction.c
> +++ b/mm/compaction.c
> @@ -1637,7 +1637,7 @@ enum compact_result try_to_compact_pages(gfp_t gfp_mask, unsigned int order,
> int may_perform_io = gfp_mask & __GFP_IO;
> struct zoneref *z;
> struct zone *zone;
> - enum compact_result rc = COMPACT_DEFERRED;
> + enum compact_result rc = COMPACT_SKIPPED;
> int all_zones_contended = COMPACT_CONTENDED_LOCK; /* init for &= op */
>
> *contended = COMPACT_CONTENDED_NONE;
> @@ -1654,8 +1654,10 @@ enum compact_result try_to_compact_pages(gfp_t gfp_mask, unsigned int order,
> enum compact_result status;
> int zone_contended;
>
> - if (compaction_deferred(zone, order))
> + if (compaction_deferred(zone, order)) {
> + rc = max_t(enum compact_result, COMPACT_DEFERRED, rc);
> continue;
> + }
>
> status = compact_zone_order(zone, order, gfp_mask, mode,
> &zone_contended, alloc_flags,
> @@ -1726,7 +1728,7 @@ enum compact_result try_to_compact_pages(gfp_t gfp_mask, unsigned int order,
> * If at least one zone wasn't deferred or skipped, we report if all
> * zones that were tried were lock contended.
> */
> - if (rc > COMPACT_SKIPPED && all_zones_contended)
> + if (rc > COMPACT_INACTIVE && all_zones_contended)
> *contended = COMPACT_CONTENDED_LOCK;
>
> return rc;
> --
> 2.8.0.rc3
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