Commit d9436498 authored by Vlastimil Babka's avatar Vlastimil Babka Committed by Linus Torvalds
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mm, compaction: more reliably increase direct compaction priority 

During reclaim/compaction loop, compaction priority can be increased by
the should_compact_retry() function, but the current code is not
optimal.  Priority is only increased when compaction_failed() is true,
which means that compaction has scanned the whole zone.  This may not
happen even after multiple attempts with a lower priority due to
parallel activity, so we might needlessly struggle on the lower
priorities and possibly run out of compaction retry attempts in the
process.

After this patch we are guaranteed at least one attempt at the highest
compaction priority even if we exhaust all retries at the lower
priorities.

Link: http://lkml.kernel.org/r/20160906135258.18335-3-vbabka@suse.cz


Signed-off-by: default avatarVlastimil Babka <vbabka@suse.cz>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Mel Gorman <mgorman@techsingularity.net>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: David Rientjes <rientjes@google.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 3250845d

mm/page_alloc.c

+19 −14
Original line number Diff line number Diff line
@@ -3160,25 +3160,23 @@ static inline bool 
should_compact_retry(struct alloc_context *ac, int order, int alloc_flags,

		     enum compact_result compact_result,

		     enum compact_priority *compact_priority,

		     int compaction_retries)

		     int *compaction_retries)

{

	int max_retries = MAX_COMPACT_RETRIES;



	if (!order)

		return false;



	if (compaction_made_progress(compact_result))

		(*compaction_retries)++;



	/*

	 * compaction considers all the zone as desperately out of memory

	 * so it doesn't really make much sense to retry except when the

	 * failure could be caused by insufficient priority

	 */

	if (compaction_failed(compact_result)) {

		if (*compact_priority > MIN_COMPACT_PRIORITY) {

			(*compact_priority)--;

			return true;

		}

		return false;

	}

	if (compaction_failed(compact_result))

		goto check_priority;



	/*

	 * make sure the compaction wasn't deferred or didn't bail out early
@@ -3199,9 +3197,19 @@ should_compact_retry(struct alloc_context *ac, int order, int alloc_flags, 
	 */

	if (order > PAGE_ALLOC_COSTLY_ORDER)

		max_retries /= 4;

	if (compaction_retries <= max_retries)

	if (*compaction_retries <= max_retries)

		return true;



	/*

	 * Make sure there are attempts at the highest priority if we exhausted

	 * all retries or failed at the lower priorities.

	 */

check_priority:

	if (*compact_priority > MIN_COMPACT_PRIORITY) {

		(*compact_priority)--;

		*compaction_retries = 0;

		return true;

	}

	return false;

}

#else
@@ -3218,7 +3226,7 @@ static inline bool 
should_compact_retry(struct alloc_context *ac, unsigned int order, int alloc_flags,

		     enum compact_result compact_result,

		     enum compact_priority *compact_priority,

		     int compaction_retries)

		     int *compaction_retries)

{

	struct zone *zone;

	struct zoneref *z;
@@ -3620,9 +3628,6 @@ retry: 
	if (page)

		goto got_pg;



	if (order && compaction_made_progress(compact_result))

		compaction_retries++;



	/* Do not loop if specifically requested */

	if (gfp_mask & __GFP_NORETRY)

		goto nopage;
@@ -3657,7 +3662,7 @@ retry: 
	if (did_some_progress > 0 &&

			should_compact_retry(ac, order, alloc_flags,

				compact_result, &compact_priority,

				compaction_retries))

				&compaction_retries))

		goto retry;



	/* Reclaim has failed us, start killing things */

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