From baf6a9a1db5a40ebfa5d3e761428d3deb2cc3a3b Mon Sep 17 00:00:00 2001 From: Vlastimil Babka Date: Mon, 8 May 2017 15:54:52 -0700 Subject: [PATCH] mm, compaction: finish whole pageblock to reduce fragmentation The main goal of direct compaction is to form a high-order page for allocation, but it should also help against long-term fragmentation when possible. Most lower-than-pageblock-order compactions are for non-movable allocations, which means that if we compact in a movable pageblock and terminate as soon as we create the high-order page, it's unlikely that the fallback heuristics will claim the whole block. Instead there might be a single unmovable page in a pageblock full of movable pages, and the next unmovable allocation might pick another pageblock and increase long-term fragmentation. To help against such scenarios, this patch changes the termination criteria for compaction so that the current pageblock is finished even though the high-order page already exists. Note that it might be possible that the high-order page formed elsewhere in the zone due to parallel activity, but this patch doesn't try to detect that. This is only done with sync compaction, because async compaction is limited to pageblock of the same migratetype, where it cannot result in a migratetype fallback. (Async compaction also eagerly skips order-aligned blocks where isolation fails, which is against the goal of migrating away as much of the pageblock as possible.) As a result of this patch, long-term memory fragmentation should be reduced. In testing based on 4.9 kernel with stress-highalloc from mmtests configured for order-4 GFP_KERNEL allocations, this patch has reduced the number of unmovable allocations falling back to movable pageblocks by 20%. The number Link: http://lkml.kernel.org/r/20170307131545.28577-9-vbabka@suse.cz Signed-off-by: Vlastimil Babka Acked-by: Mel Gorman Acked-by: Johannes Weiner Cc: Joonsoo Kim Cc: David Rientjes Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- mm/compaction.c | 36 ++++++++++++++++++++++++++++++++++-- mm/internal.h | 1 + 2 files changed, 35 insertions(+), 2 deletions(-) diff --git a/mm/compaction.c b/mm/compaction.c index 206847d35978..613c59e928cb 100644 --- a/mm/compaction.c +++ b/mm/compaction.c @@ -1318,6 +1318,17 @@ static enum compact_result __compact_finished(struct zone *zone, if (is_via_compact_memory(cc->order)) return COMPACT_CONTINUE; + if (cc->finishing_block) { + /* + * We have finished the pageblock, but better check again that + * we really succeeded. + */ + if (IS_ALIGNED(cc->migrate_pfn, pageblock_nr_pages)) + cc->finishing_block = false; + else + return COMPACT_CONTINUE; + } + /* Direct compactor: Is a suitable page free? */ for (order = cc->order; order < MAX_ORDER; order++) { struct free_area *area = &zone->free_area[order]; @@ -1338,8 +1349,29 @@ static enum compact_result __compact_finished(struct zone *zone, * other migratetype buddy lists. */ if (find_suitable_fallback(area, order, migratetype, - true, &can_steal) != -1) - return COMPACT_SUCCESS; + true, &can_steal) != -1) { + + /* movable pages are OK in any pageblock */ + if (migratetype == MIGRATE_MOVABLE) + return COMPACT_SUCCESS; + + /* + * We are stealing for a non-movable allocation. Make + * sure we finish compacting the current pageblock + * first so it is as free as possible and we won't + * have to steal another one soon. This only applies + * to sync compaction, as async compaction operates + * on pageblocks of the same migratetype. + */ + if (cc->mode == MIGRATE_ASYNC || + IS_ALIGNED(cc->migrate_pfn, + pageblock_nr_pages)) { + return COMPACT_SUCCESS; + } + + cc->finishing_block = true; + return COMPACT_CONTINUE; + } } return COMPACT_NO_SUITABLE_PAGE; diff --git a/mm/internal.h b/mm/internal.h index e7e709fd3043..0e4f558412fb 100644 --- a/mm/internal.h +++ b/mm/internal.h @@ -202,6 +202,7 @@ struct compact_control { bool direct_compaction; /* False from kcompactd or /proc/... */ bool whole_zone; /* Whole zone should/has been scanned */ bool contended; /* Signal lock or sched contention */ + bool finishing_block; /* Finishing current pageblock */ }; unsigned long