From 984fdba6a32e4e9819ebc06ca3acec6582ffd99f Mon Sep 17 00:00:00 2001 From: Vlastimil Babka Date: Fri, 7 Oct 2016 16:57:57 -0700 Subject: [PATCH] mm, compaction: use proper alloc_flags in __compaction_suitable() The __compaction_suitable() function checks the low watermark plus a compact_gap() gap to decide if there's enough free memory to perform compaction. This check uses direct compactor's alloc_flags, but that's wrong, since these flags are not applicable for freepage isolation. For example, alloc_flags may indicate access to memory reserves, making compaction proceed, and then fail watermark check during the isolation. A similar problem exists for ALLOC_CMA, which may be part of alloc_flags, but not during freepage isolation. In this case however it makes sense to use ALLOC_CMA both in __compaction_suitable() and __isolate_free_page(), since there's actually nothing preventing the freepage scanner to isolate from CMA pageblocks, with the assumption that a page that could be migrated once by compaction can be migrated also later by CMA allocation. Thus we should count pages in CMA pageblocks when considering compaction suitability and when isolating freepages. To sum up, this patch should remove some false positives from __compaction_suitable(), and allow compaction to proceed when free pages required for compaction reside in the CMA pageblocks. Link: http://lkml.kernel.org/r/20160810091226.6709-10-vbabka@suse.cz Signed-off-by: Vlastimil Babka Tested-by: Lorenzo Stoakes Cc: Michal Hocko Cc: Mel Gorman Cc: Joonsoo Kim Cc: David Rientjes Cc: Rik van Riel Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- mm/compaction.c | 12 ++++++++++-- mm/page_alloc.c | 2 +- 2 files changed, 11 insertions(+), 3 deletions(-) diff --git a/mm/compaction.c b/mm/compaction.c index bbf41ee99142..658c009d60cc 100644 --- a/mm/compaction.c +++ b/mm/compaction.c @@ -1392,11 +1392,19 @@ static enum compact_result __compaction_suitable(struct zone *zone, int order, /* * Watermarks for order-0 must be met for compaction to be able to - * isolate free pages for migration targets. + * isolate free pages for migration targets. This means that the + * watermark and alloc_flags have to match, or be more pessimistic than + * the check in __isolate_free_page(). We don't use the direct + * compactor's alloc_flags, as they are not relevant for freepage + * isolation. We however do use the direct compactor's classzone_idx to + * skip over zones where lowmem reserves would prevent allocation even + * if compaction succeeds. + * ALLOC_CMA is used, as pages in CMA pageblocks are considered + * suitable migration targets */ watermark = low_wmark_pages(zone) + compact_gap(order); if (!__zone_watermark_ok(zone, 0, watermark, classzone_idx, - alloc_flags, wmark_target)) + ALLOC_CMA, wmark_target)) return COMPACT_SKIPPED; /* diff --git a/mm/page_alloc.c b/mm/page_alloc.c index a2214c64ed3c..637b0e907df0 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -2491,7 +2491,7 @@ int __isolate_free_page(struct page *page, unsigned int order) if (!is_migrate_isolate(mt)) { /* Obey watermarks as if the page was being allocated */ watermark = low_wmark_pages(zone) + (1 << order); - if (!zone_watermark_ok(zone, 0, watermark, 0, 0)) + if (!zone_watermark_ok(zone, 0, watermark, 0, ALLOC_CMA)) return 0; __mod_zone_freepage_state(zone, -(1UL << order), mt);