Commit 49433085 authored by Vlastimil Babka's avatar Vlastimil Babka Committed by Linus Torvalds
Browse files

mm, compaction: raise compaction priority after it withdrawns 

Mike Kravetz reports that "hugetlb allocations could stall for minutes or
hours when should_compact_retry() would return true more often then it
should.  Specifically, this was in the case where compact_result was
COMPACT_DEFERRED and COMPACT_PARTIAL_SKIPPED and no progress was being
made."

The problem is that the compaction_withdrawn() test in
should_compact_retry() includes compaction outcomes that are only possible
on low compaction priority, and results in a retry without increasing the
priority.  This may result in furter reclaim, and more incomplete
compaction attempts.

With this patch, compaction priority is raised when possible, or
should_compact_retry() returns false.

The COMPACT_SKIPPED result doesn't really fit together with the other
outcomes in compaction_withdrawn(), as that's a result caused by
insufficient order-0 pages, not due to low compaction priority.  With this
patch, it is moved to a new compaction_needs_reclaim() function, and for
that outcome we keep the current logic of retrying if it looks like
reclaim will be able to help.

Link: http://lkml.kernel.org/r/20190806014744.15446-4-mike.kravetz@oracle.com


Reported-by: default avatarMike Kravetz <mike.kravetz@oracle.com>
Signed-off-by: default avatarVlastimil Babka <vbabka@suse.cz>
Signed-off-by: default avatarMike Kravetz <mike.kravetz@oracle.com>
Tested-by: default avatarMike Kravetz <mike.kravetz@oracle.com>
Cc: Hillf Danton <hdanton@sina.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Michal Hocko <mhocko@kernel.org>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 5ee04716

include/linux/compaction.h

+17 −5
Original line number Diff line number Diff line
@@ -129,11 +129,8 @@ static inline bool compaction_failed(enum compact_result result) 
	return false;

}



/*

 * Compaction  has backed off for some reason. It might be throttling or

 * lock contention. Retrying is still worthwhile.

 */

static inline bool compaction_withdrawn(enum compact_result result)

/* Compaction needs reclaim to be performed first, so it can continue. */

static inline bool compaction_needs_reclaim(enum compact_result result)

{

	/*

	 * Compaction backed off due to watermark checks for order-0
@@ -142,6 +139,16 @@ static inline bool compaction_withdrawn(enum compact_result result) 
	if (result == COMPACT_SKIPPED)

		return true;



	return false;

}



/*

 * Compaction has backed off for some reason after doing some work or none

 * at all. It might be throttling or lock contention. Retrying might be still

 * worthwhile, but with a higher priority if allowed.

 */

static inline bool compaction_withdrawn(enum compact_result result)

{

	/*

	 * If compaction is deferred for high-order allocations, it is

	 * because sync compaction recently failed. If this is the case
@@ -207,6 +214,11 @@ static inline bool compaction_failed(enum compact_result result) 
	return false;

}



static inline bool compaction_needs_reclaim(enum compact_result result)

{

	return false;

}



static inline bool compaction_withdrawn(enum compact_result result)

{

	return true;

mm/page_alloc.c

+12 −4
Original line number Diff line number Diff line
@@ -3954,15 +3954,23 @@ should_compact_retry(struct alloc_context *ac, int order, int alloc_flags, 
	if (compaction_failed(compact_result))

		goto check_priority;



	/*

	 * compaction was skipped because there are not enough order-0 pages

	 * to work with, so we retry only if it looks like reclaim can help.

	 */

	if (compaction_needs_reclaim(compact_result)) {

		ret = compaction_zonelist_suitable(ac, order, alloc_flags);

		goto out;

	}



	/*

	 * make sure the compaction wasn't deferred or didn't bail out early

	 * due to locks contention before we declare that we should give up.

	 * But do not retry if the given zonelist is not suitable for

	 * compaction.

	 * But the next retry should use a higher priority if allowed, so

	 * we don't just keep bailing out endlessly.

	 */

	if (compaction_withdrawn(compact_result)) {

		ret = compaction_zonelist_suitable(ac, order, alloc_flags);

		goto out;

		goto check_priority;

	}



	/*

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