When pageblocks get fragmented, watermarks are artifically boosted to reclaim pages to avoid further fragmentation events. However, compaction is often either fragmentation-neutral or moving movable pages away from unmovable/reclaimable pages. As the true watermarks are preserved, allow compaction to ignore the boost factor. The expected impact is very slight as the main benefit is that compaction is slightly more likely to succeed when the system has been fragmented very recently. On both 1-socket and 2-socket machines for THP-intensive allocation during fragmentation the success rate was increased by less than 1% which is marginal. 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 57ba9d1da519..05c9a81d54ed 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -2958,7 +2958,7 @@ 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
