Re: [PATCH 06/14] mm, compaction: Update compaction_result ordering

[Hillf Danton]

> 
> From: Michal Hocko <mhocko@xxxxxxxx>
> 
> compaction_result will be used as the primary feedback channel for
> compaction users. At the same time try_to_compact_pages (and potentially
> others) assume a certain ordering where a more specific feedback takes
> precendence. This gets a bit awkward when we have conflicting feedback
> from different zones. E.g one returing COMPACT_COMPLETE meaning the full
> zone has been scanned without any outcome while other returns with
> COMPACT_PARTIAL aka made some progress. The caller should get
> COMPACT_PARTIAL because that means that the compaction still can make
> some progress. The same applies for COMPACT_PARTIAL vs.
> COMPACT_PARTIAL_SKIPPED. Reorder PARTIAL to be the largest one so the
> larger the value is the more progress we have done.
> 
> Acked-by: Vlastimil Babka <vbabka@xxxxxxx>
> Signed-off-by: Michal Hocko <mhocko@xxxxxxxx>
> ---

Acked-by: Hillf Danton <hillf.zj@xxxxxxxxxxxxxxx>

>  include/linux/compaction.h | 26 ++++++++++++++++----------
>  1 file changed, 16 insertions(+), 10 deletions(-)
> 
> diff --git a/include/linux/compaction.h b/include/linux/compaction.h
> index 7c4de92d12cc..a7b9091ff349 100644
> --- a/include/linux/compaction.h
> +++ b/include/linux/compaction.h
> @@ -4,6 +4,8 @@
>  /* Return values for compact_zone() and try_to_compact_pages() */
>  /* When adding new states, please adjust include/trace/events/compaction.h */
>  enum compact_result {
> +	/* For more detailed tracepoint output - internal to compaction */
> +	COMPACT_NOT_SUITABLE_ZONE,
>  	/*
>  	 * compaction didn't start as it was not possible or direct reclaim
>  	 * was more suitable
> @@ -11,30 +13,34 @@ enum compact_result {
>  	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,
> 
> +	/* For more detailed tracepoint output - internal to compaction */
> +	COMPACT_NO_SUITABLE_PAGE,
>  	/* compaction should continue to another pageblock */
>  	COMPACT_CONTINUE,
> +
>  	/*
> -	 * direct compaction partially compacted a zone and there are suitable
> -	 * pages
> +	 * The full zone was compacted scanned but wasn't successfull to compact
> +	 * suitable pages.
>  	 */
> -	COMPACT_PARTIAL,
> +	COMPACT_COMPLETE,
>  	/*
>  	 * direct compaction has scanned part of the zone but wasn't successfull
>  	 * to compact suitable pages.
>  	 */
>  	COMPACT_PARTIAL_SKIPPED,
> +
> +	/* compaction terminated prematurely due to lock contentions */
> +	COMPACT_CONTENDED,
> +
>  	/*
> -	 * The full zone was compacted scanned but wasn't successfull to compact
> -	 * suitable pages.
> +	 * direct compaction partially compacted a zone and there might be
> +	 * suitable pages
>  	 */
> -	COMPACT_COMPLETE,
> -	/* For more detailed tracepoint output */
> -	COMPACT_NO_SUITABLE_PAGE,
> -	COMPACT_NOT_SUITABLE_ZONE,
> -	COMPACT_CONTENDED,
> +	COMPACT_PARTIAL,
>  };
> 
>  /* Used to signal whether compaction detected need_sched() or lock contention */
> --
> 2.8.0.rc3