From: Vlastimil Babka <vbabka@xxxxxxx> Subject: mm, compaction: use correct watermark when checking compaction success The __compact_finished() function uses low watermark in a check that has to pass if the direct compaction is to finish and allocation should succeed. This is too pessimistic, as the allocation will typically use min watermark. It may happen that during compaction, we drop below the low watermark (due to parallel activity), but still form the target high-order page. By checking against low watermark, we might needlessly continue compaction. Similarly, __compaction_suitable() uses low watermark in a check whether allocation can succeed without compaction. Again, this is unnecessarily pessimistic. After this patch, these check will use direct compactor's alloc_flags to determine the watermark, which is effectively the min watermark. Link: http://lkml.kernel.org/r/20160810091226.6709-8-vbabka@xxxxxxx Signed-off-by: Vlastimil Babka <vbabka@xxxxxxx> Tested-by: Lorenzo Stoakes <lstoakes@xxxxxxxxx> Acked-by: Michal Hocko <mhocko@xxxxxxxx> Cc: Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx> Cc: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx> Cc: David Rientjes <rientjes@xxxxxxxxxx> Cc: Rik van Riel <riel@xxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- mm/compaction.c | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-) diff -puN mm/compaction.c~mm-compaction-use-correct-watermark-when-checking-compaction-success mm/compaction.c --- a/mm/compaction.c~mm-compaction-use-correct-watermark-when-checking-compaction-success +++ a/mm/compaction.c @@ -1316,7 +1316,7 @@ static enum compact_result __compact_fin return COMPACT_CONTINUE; /* Compaction run is not finished if the watermark is not met */ - watermark = low_wmark_pages(zone); + watermark = zone->watermark[cc->alloc_flags & ALLOC_WMARK_MASK]; if (!zone_watermark_ok(zone, cc->order, watermark, cc->classzone_idx, cc->alloc_flags)) @@ -1381,7 +1381,7 @@ static enum compact_result __compaction_ if (is_via_compact_memory(order)) return COMPACT_CONTINUE; - watermark = low_wmark_pages(zone); + watermark = zone->watermark[alloc_flags & ALLOC_WMARK_MASK]; /* * If watermarks for high-order allocation are already met, there * should be no need for compaction at all. @@ -1395,7 +1395,7 @@ static enum compact_result __compaction_ * This is because during migration, copies of pages need to be * allocated and for a short time, the footprint is higher */ - watermark += (2UL << order); + watermark = low_wmark_pages(zone) + (2UL << order); if (!__zone_watermark_ok(zone, 0, watermark, classzone_idx, alloc_flags, wmark_target)) return COMPACT_SKIPPED; _ -- To unsubscribe from this list: send the line "unsubscribe mm-commits" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
