Re: [PATCH 05/14] mm, compaction: distinguish between full and partial COMPACT_COMPLETE

[Hillf Danton]

> 
> From: Michal Hocko <mhocko@xxxxxxxx>
> 
> COMPACT_COMPLETE now means that compaction and free scanner met. This is
> not very useful information if somebody just wants to use this feedback
> and make any decisions based on that. The current caller might be a poor
> guy who just happened to scan tiny portion of the zone and that could be
> the reason no suitable pages were compacted. Make sure we distinguish
> the full and partial zone walks.
> 
> Consumers should treat COMPACT_PARTIAL_SKIPPED as a potential success
> and be optimistic in retrying.
> 
> The existing users of COMPACT_COMPLETE are conservatively changed to
> use COMPACT_PARTIAL_SKIPPED as well but some of them should be probably
> reconsidered and only defer the compaction only for COMPACT_COMPLETE
> with the new semantic.
> 
> This patch shouldn't introduce any functional changes.
> 
> Acked-by: Vlastimil Babka <vbabka@xxxxxxx>
> Signed-off-by: Michal Hocko <mhocko@xxxxxxxx>
> ---

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

>  include/linux/compaction.h        | 10 +++++++++-
>  include/trace/events/compaction.h |  1 +
>  mm/compaction.c                   | 14 +++++++++++---
>  mm/internal.h                     |  1 +
>  4 files changed, 22 insertions(+), 4 deletions(-)
> 
> diff --git a/include/linux/compaction.h b/include/linux/compaction.h
> index 7e177d111c39..7c4de92d12cc 100644
> --- a/include/linux/compaction.h
> +++ b/include/linux/compaction.h
> @@ -21,7 +21,15 @@ enum compact_result {
>  	 * pages
>  	 */
>  	COMPACT_PARTIAL,
> -	/* The full zone was compacted */
> +	/*
> +	 * direct compaction has scanned part of the zone but wasn't successfull
> +	 * to compact suitable pages.
> +	 */
> +	COMPACT_PARTIAL_SKIPPED,
> +	/*
> +	 * The full zone was compacted scanned but wasn't successfull to compact
> +	 * suitable pages.
> +	 */
>  	COMPACT_COMPLETE,
>  	/* For more detailed tracepoint output */
>  	COMPACT_NO_SUITABLE_PAGE,
> diff --git a/include/trace/events/compaction.h b/include/trace/events/compaction.h
> index 6ba16c86d7db..36e2d6fb1360 100644
> --- a/include/trace/events/compaction.h
> +++ b/include/trace/events/compaction.h
> @@ -14,6 +14,7 @@
>  	EM( COMPACT_DEFERRED,		"deferred")		\
>  	EM( COMPACT_CONTINUE,		"continue")		\
>  	EM( COMPACT_PARTIAL,		"partial")		\
> +	EM( COMPACT_PARTIAL_SKIPPED,	"partial_skipped")	\
>  	EM( COMPACT_COMPLETE,		"complete")		\
>  	EM( COMPACT_NO_SUITABLE_PAGE,	"no_suitable_page")	\
>  	EM( COMPACT_NOT_SUITABLE_ZONE,	"not_suitable_zone")	\
> diff --git a/mm/compaction.c b/mm/compaction.c
> index 13709e33a2fc..e2e487cea5ea 100644
> --- a/mm/compaction.c
> +++ b/mm/compaction.c
> @@ -1304,7 +1304,10 @@ static enum compact_result __compact_finished(struct zone *zone, struct compact_
>  		if (cc->direct_compaction)
>  			zone->compact_blockskip_flush = true;
> 
> -		return COMPACT_COMPLETE;
> +		if (cc->whole_zone)
> +			return COMPACT_COMPLETE;
> +		else
> +			return COMPACT_PARTIAL_SKIPPED;
>  	}
> 
>  	if (is_via_compact_memory(cc->order))
> @@ -1463,6 +1466,10 @@ static enum compact_result compact_zone(struct zone *zone, struct compact_contro
>  		zone->compact_cached_migrate_pfn[0] = cc->migrate_pfn;
>  		zone->compact_cached_migrate_pfn[1] = cc->migrate_pfn;
>  	}
> +
> +	if (cc->migrate_pfn == start_pfn)
> +		cc->whole_zone = true;
> +
>  	cc->last_migrated_pfn = 0;
> 
>  	trace_mm_compaction_begin(start_pfn, cc->migrate_pfn,
> @@ -1693,7 +1700,8 @@ enum compact_result try_to_compact_pages(gfp_t gfp_mask, unsigned int order,
>  			goto break_loop;
>  		}
> 
> -		if (mode != MIGRATE_ASYNC && status == COMPACT_COMPLETE) {
> +		if (mode != MIGRATE_ASYNC && (status == COMPACT_COMPLETE ||
> +					status == COMPACT_PARTIAL_SKIPPED)) {
>  			/*
>  			 * We think that allocation won't succeed in this zone
>  			 * so we defer compaction there. If it ends up
> @@ -1939,7 +1947,7 @@ static void kcompactd_do_work(pg_data_t *pgdat)
>  						cc.classzone_idx, 0)) {
>  			success = true;
>  			compaction_defer_reset(zone, cc.order, false);
> -		} else if (status == COMPACT_COMPLETE) {
> +		} else if (status == COMPACT_PARTIAL_SKIPPED || status == COMPACT_COMPLETE) {
>  			/*
>  			 * We use sync migration mode here, so we defer like
>  			 * sync direct compaction does.
> diff --git a/mm/internal.h b/mm/internal.h
> index e9aacea1a0d1..4423dfe69382 100644
> --- a/mm/internal.h
> +++ b/mm/internal.h
> @@ -182,6 +182,7 @@ struct compact_control {
>  	enum migrate_mode mode;		/* Async or sync migration mode */
>  	bool ignore_skip_hint;		/* Scan blocks even if marked skip */
>  	bool direct_compaction;		/* False from kcompactd or /proc/... */
> +	bool whole_zone;		/* Whole zone has been scanned */
>  	int order;			/* order a direct compactor needs */
>  	const gfp_t gfp_mask;		/* gfp mask of a direct compactor */
>  	const int alloc_flags;		/* alloc flags of a direct compactor */
> --
> 2.8.0.rc3