[PATCH 09/14] mm, compaction: Ignore the fragmentation avoidance boost for isolation and compaction

Mel Gorman
2018-12-14T23:03:30Z

When pageblocks get fragmented, watermarks are artifically boosted to pages
are reclaimed to avoid further fragmentation events. However, compaction
is often either fragmentation-neutral or moving movable pages away from
unmovable/reclaimable pages. As the actual watermarks are preserved,
allow compaction to ignore the boost factor.

1-socket thpscale
4.20.0-rc6 4.20.0-rc6
finishscan-v1r4 noboost-v1r4
Amean fault-both-1 0.00 ( 0.00%) 0.00 * 0.00%*
Amean fault-both-3 3849.90 ( 0.00%) 3753.53 ( 2.50%)
Amean fault-both-5 5054.13 ( 0.00%) 5396.32 ( -6.77%)
Amean fault-both-7 7061.77 ( 0.00%) 7393.46 ( -4.70%)
Amean fault-both-12 11560.59 ( 0.00%) 12155.50 ( -5.15%)
Amean fault-both-18 16120.15 ( 0.00%) 16445.96 ( -2.02%)
Amean fault-both-24 19804.31 ( 0.00%) 20465.03 ( -3.34%)
Amean fault-both-30 25018.73 ( 0.00%) 20813.54 * 16.81%*
Amean fault-both-32 24380.19 ( 0.00%) 22384.02 ( 8.19%)

The impact on the scan rates is a mixed bag because this patch is very
sensitive to timing and whether the boost was active or not. However,
detailed tracing indicated that failure of migration due to a premature
ENOMEM triggered by watermark checks were eliminated.

Signed-off-by: Mel Gorman <mgorman@techsingularity.net>
---
mm/page_alloc.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 80535cd55a92..c7b80e62bfd9 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -3043,7 +3043,7 @@ int __isolate_free_page(struct page *page, unsigned int order)
* watermark, because we already know our high-order page
* exists.
*/
- watermark = min_wmark_pages(zone) + (1UL << order);
+ watermark = zone->_watermark[WMARK_MIN] + (1UL << order);
if (!zone_watermark_ok(zone, 0, watermark, 0, ALLOC_CMA))
return 0;

--
2.16.4