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Commit dc67647b authored by Joonsoo Kim's avatar Joonsoo Kim Committed by Linus Torvalds
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mm/cma: change fallback behaviour for CMA freepage 



Freepage with MIGRATE_CMA can be used only for MIGRATE_MOVABLE and they
should not be expanded to other migratetype buddy list to protect them
from unmovable/reclaimable allocation.  Implementing these requirements in
__rmqueue_fallback(), that is, finding largest possible block of freepage
has bad effect that high order freepage with MIGRATE_CMA are broken
continually although there are suitable order CMA freepage.  Reason is
that they are not be expanded to other migratetype buddy list and next
__rmqueue_fallback() invocation try to finds another largest block of
freepage and break it again.  So, MIGRATE_CMA fallback should be handled
separately.  This patch introduces __rmqueue_cma_fallback(), that just
wrapper of __rmqueue_smallest() and call it before __rmqueue_fallback() if
migratetype == MIGRATE_MOVABLE.

This results in unintended behaviour change that MIGRATE_CMA freepage is
always used first rather than other migratetype as movable allocation's
fallback.  But, as already mentioned above, MIGRATE_CMA can be used only
for MIGRATE_MOVABLE, so it is better to use MIGRATE_CMA freepage first as
much as possible.  Otherwise, we needlessly take up precious freepages
with other migratetype and increase chance of fragmentation.

Signed-off-by: default avatarJoonsoo Kim <iamjoonsoo.kim@lge.com>
Acked-by: default avatarVlastimil Babka <vbabka@suse.cz>
Cc: Mel Gorman <mgorman@suse.de>
Cc: David Rientjes <rientjes@google.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Zhang Yanfei <zhangyanfei@cn.fujitsu.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 30467e0b

mm/page_alloc.c

+19 −17
Original line number Diff line number Diff line
@@ -1032,11 +1032,9 @@ struct page *__rmqueue_smallest(struct zone *zone, unsigned int order, 
static int fallbacks[MIGRATE_TYPES][4] = {

	[MIGRATE_UNMOVABLE]   = { MIGRATE_RECLAIMABLE, MIGRATE_MOVABLE,     MIGRATE_RESERVE },

	[MIGRATE_RECLAIMABLE] = { MIGRATE_UNMOVABLE,   MIGRATE_MOVABLE,     MIGRATE_RESERVE },

	[MIGRATE_MOVABLE]     = { MIGRATE_RECLAIMABLE, MIGRATE_UNMOVABLE,   MIGRATE_RESERVE },

#ifdef CONFIG_CMA

	[MIGRATE_MOVABLE]     = { MIGRATE_CMA,         MIGRATE_RECLAIMABLE, MIGRATE_UNMOVABLE, MIGRATE_RESERVE },

	[MIGRATE_CMA]         = { MIGRATE_RESERVE }, /* Never used */

#else

	[MIGRATE_MOVABLE]     = { MIGRATE_RECLAIMABLE, MIGRATE_UNMOVABLE,   MIGRATE_RESERVE },

#endif

	[MIGRATE_RESERVE]     = { MIGRATE_RESERVE }, /* Never used */

#ifdef CONFIG_MEMORY_ISOLATION
@@ -1044,6 +1042,17 @@ static int fallbacks[MIGRATE_TYPES][4] = { 
#endif

};



#ifdef CONFIG_CMA

static struct page *__rmqueue_cma_fallback(struct zone *zone,

					unsigned int order)

{

	return __rmqueue_smallest(zone, order, MIGRATE_CMA);

}

#else

static inline struct page *__rmqueue_cma_fallback(struct zone *zone,

					unsigned int order) { return NULL; }

#endif



/*

 * Move the free pages in a range to the free lists of the requested type.

 * Note that start_page and end_pages are not aligned on a pageblock
@@ -1195,19 +1204,8 @@ __rmqueue_fallback(struct zone *zone, unsigned int order, int start_migratetype) 
					struct page, lru);

			area->nr_free--;



			if (!is_migrate_cma(migratetype)) {

				try_to_steal_freepages(zone, page,

							start_migratetype,

			try_to_steal_freepages(zone, page, start_migratetype,

								migratetype);

			} else {

				/*

				 * When borrowing from MIGRATE_CMA, we need to

				 * release the excess buddy pages to CMA

				 * itself, and we do not try to steal extra

				 * free pages.

				 */

				buddy_type = migratetype;

			}



			/* Remove the page from the freelists */

			list_del(&page->lru);
@@ -1249,6 +1247,10 @@ static struct page *__rmqueue(struct zone *zone, unsigned int order, 
	page = __rmqueue_smallest(zone, order, migratetype);



	if (unlikely(!page) && migratetype != MIGRATE_RESERVE) {

		if (migratetype == MIGRATE_MOVABLE)

			page = __rmqueue_cma_fallback(zone, order);



		if (!page)

			page = __rmqueue_fallback(zone, order, migratetype);



		/*