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

[Mel Gorman]

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@xxxxxxxxxxxxxxxxxxx>
---
 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