Commit 8348faf9 authored by Vlastimil Babka's avatar Vlastimil Babka Committed by Linus Torvalds

mm, compaction: require only min watermarks for non-costly orders

The __compaction_suitable() function checks the low watermark plus a
compact_gap() gap to decide if there's enough free memory to perform
compaction.  Then __isolate_free_page uses low watermark check to decide
if particular free page can be isolated.  In the latter case, using low
watermark is needlessly pessimistic, as the free page isolations are
only temporary.  For __compaction_suitable() the higher watermark makes
sense for high-order allocations where more freepages increase the
chance of success, and we can typically fail with some order-0 fallback
when the system is struggling to reach that watermark.  But for
low-order allocation, forming the page should not be that hard.  So
using low watermark here might just prevent compaction from even trying,
and eventually lead to OOM killer even if we are above min watermarks.

So after this patch, we use min watermark for non-costly orders in
__compaction_suitable(), and for all orders in __isolate_free_page().

[vbabka@suse.cz: clarify __isolate_free_page() comment]
 Link: http://lkml.kernel.org/r/7ae4baec-4eca-e70b-2a69-94bea4fb19fa@suse.cz
Link: http://lkml.kernel.org/r/20160810091226.6709-11-vbabka@suse.czSigned-off-by: default avatarVlastimil Babka <vbabka@suse.cz>
Tested-by: default avatarLorenzo Stoakes <lstoakes@gmail.com>
Acked-by: default avatarMichal Hocko <mhocko@suse.com>
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>
Signed-off-by: default avatarVlastimil Babka <vbabka@suse.cz>
Tested-by: default avatarLorenzo Stoakes <lstoakes@gmail.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 984fdba6
...@@ -1399,10 +1399,14 @@ static enum compact_result __compaction_suitable(struct zone *zone, int order, ...@@ -1399,10 +1399,14 @@ static enum compact_result __compaction_suitable(struct zone *zone, int order,
* isolation. We however do use the direct compactor's classzone_idx to * isolation. We however do use the direct compactor's classzone_idx to
* skip over zones where lowmem reserves would prevent allocation even * skip over zones where lowmem reserves would prevent allocation even
* if compaction succeeds. * if compaction succeeds.
* For costly orders, we require low watermark instead of min for
* compaction to proceed to increase its chances.
* ALLOC_CMA is used, as pages in CMA pageblocks are considered * ALLOC_CMA is used, as pages in CMA pageblocks are considered
* suitable migration targets * suitable migration targets
*/ */
watermark = low_wmark_pages(zone) + compact_gap(order); watermark = (order > PAGE_ALLOC_COSTLY_ORDER) ?
low_wmark_pages(zone) : min_wmark_pages(zone);
watermark += compact_gap(order);
if (!__zone_watermark_ok(zone, 0, watermark, classzone_idx, if (!__zone_watermark_ok(zone, 0, watermark, classzone_idx,
ALLOC_CMA, wmark_target)) ALLOC_CMA, wmark_target))
return COMPACT_SKIPPED; return COMPACT_SKIPPED;
......
...@@ -2489,8 +2489,13 @@ int __isolate_free_page(struct page *page, unsigned int order) ...@@ -2489,8 +2489,13 @@ int __isolate_free_page(struct page *page, unsigned int order)
mt = get_pageblock_migratetype(page); mt = get_pageblock_migratetype(page);
if (!is_migrate_isolate(mt)) { if (!is_migrate_isolate(mt)) {
/* Obey watermarks as if the page was being allocated */ /*
watermark = low_wmark_pages(zone) + (1 << order); * Obey watermarks as if the page was being allocated. We can
* emulate a high-order watermark check with a raised order-0
* watermark, because we already know our high-order page
* exists.
*/
watermark = min_wmark_pages(zone) + (1UL << order);
if (!zone_watermark_ok(zone, 0, watermark, 0, ALLOC_CMA)) if (!zone_watermark_ok(zone, 0, watermark, 0, ALLOC_CMA))
return 0; return 0;
......
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