From 06ed29989f39f5129d4f76f4a2d7ce2efa46a6a1 Mon Sep 17 00:00:00 2001 From: Vlastimil Babka Date: Fri, 7 Oct 2016 16:57:35 -0700 Subject: [PATCH] mm, compaction: make whole_zone flag ignore cached scanner positions Patch series "make direct compaction more deterministic") This is mostly a followup to Michal's oom detection rework, which highlighted the need for direct compaction to provide better feedback in reclaim/compaction loop, so that it can reliably recognize when compaction cannot make further progress, and allocation should invoke OOM killer or fail. We've discussed this at LSF/MM [1] where I proposed expanding the async/sync migration mode used in compaction to more general "priorities". This patchset adds one new priority that just overrides all the heuristics and makes compaction fully scan all zones. I don't currently think that we need more fine-grained priorities, but we'll see. Other than that there's some smaller fixes and cleanups, mainly related to the THP-specific hacks. I've tested this with stress-highalloc in GFP_KERNEL order-4 and THP-like order-9 scenarios. There's some improvement for compaction stats for the order-4, which is likely due to the better watermarks handling. In the previous version I reported mostly noise wrt compaction stats, and decreased direct reclaim - now the reclaim is without difference. I believe this is due to the less aggressive compaction priority increase in patch 6. "before" is a mmotm tree prior to 4.7 release plus the first part of the series that was sent and merged separately before after order-4: Compaction stalls 27216 30759 Compaction success 19598 25475 Compaction failures 7617 5283 Page migrate success 370510 464919 Page migrate failure 25712 27987 Compaction pages isolated 849601 1041581 Compaction migrate scanned 143146541 101084990 Compaction free scanned 208355124 144863510 Compaction cost 1403 1210 order-9: Compaction stalls 7311 7401 Compaction success 1634 1683 Compaction failures 5677 5718 Page migrate success 194657 183988 Page migrate failure 4753 4170 Compaction pages isolated 498790 456130 Compaction migrate scanned 565371 524174 Compaction free scanned 4230296 4250744 Compaction cost 215 203 [1] https://lwn.net/Articles/684611/ This patch (of 11): A recent patch has added whole_zone flag that compaction sets when scanning starts from the zone boundary, in order to report that zone has been fully scanned in one attempt. For allocations that want to try really hard or cannot fail, we will want to introduce a mode where scanning whole zone is guaranteed regardless of the cached positions. This patch reuses the whole_zone flag in a way that if it's already passed true to compaction, the cached scanner positions are ignored. Employing this flag during reclaim/compaction loop will be done in the next patch. This patch however converts compaction invoked from userspace via procfs to use this flag. Before this patch, the cached positions were first reset to zone boundaries and then read back from struct zone, so there was a window where a parallel compaction could replace the reset values, making the manual compaction less effective. Using the flag instead of performing reset is more robust. [akpm@linux-foundation.org: coding-style fixes] Link: http://lkml.kernel.org/r/20160810091226.6709-2-vbabka@suse.cz Signed-off-by: Vlastimil Babka Tested-by: Lorenzo Stoakes Acked-by: 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 | 43 +++++++++++++++++++++---------------------- mm/internal.h | 2 +- 2 files changed, 22 insertions(+), 23 deletions(-) diff --git a/mm/compaction.c b/mm/compaction.c index 9affb2908304..c684ca141e4b 100644 --- a/mm/compaction.c +++ b/mm/compaction.c @@ -1492,23 +1492,29 @@ static enum compact_result compact_zone(struct zone *zone, struct compact_contro /* * Setup to move all movable pages to the end of the zone. Used cached - * information on where the scanners should start but check that it - * is initialised by ensuring the values are within zone boundaries. + * information on where the scanners should start (unless we explicitly + * want to compact the whole zone), but check that it is initialised + * by ensuring the values are within zone boundaries. */ - cc->migrate_pfn = zone->compact_cached_migrate_pfn[sync]; - cc->free_pfn = zone->compact_cached_free_pfn; - if (cc->free_pfn < start_pfn || cc->free_pfn >= end_pfn) { - cc->free_pfn = pageblock_start_pfn(end_pfn - 1); - zone->compact_cached_free_pfn = cc->free_pfn; - } - if (cc->migrate_pfn < start_pfn || cc->migrate_pfn >= end_pfn) { + if (cc->whole_zone) { cc->migrate_pfn = start_pfn; - zone->compact_cached_migrate_pfn[0] = cc->migrate_pfn; - zone->compact_cached_migrate_pfn[1] = cc->migrate_pfn; - } + cc->free_pfn = pageblock_start_pfn(end_pfn - 1); + } else { + cc->migrate_pfn = zone->compact_cached_migrate_pfn[sync]; + cc->free_pfn = zone->compact_cached_free_pfn; + if (cc->free_pfn < start_pfn || cc->free_pfn >= end_pfn) { + cc->free_pfn = pageblock_start_pfn(end_pfn - 1); + zone->compact_cached_free_pfn = cc->free_pfn; + } + if (cc->migrate_pfn < start_pfn || cc->migrate_pfn >= end_pfn) { + cc->migrate_pfn = start_pfn; + zone->compact_cached_migrate_pfn[0] = cc->migrate_pfn; + zone->compact_cached_migrate_pfn[1] = cc->migrate_pfn; + } - if (cc->migrate_pfn == start_pfn) - cc->whole_zone = true; + if (cc->migrate_pfn == start_pfn) + cc->whole_zone = true; + } cc->last_migrated_pfn = 0; @@ -1747,14 +1753,6 @@ static void __compact_pgdat(pg_data_t *pgdat, struct compact_control *cc) INIT_LIST_HEAD(&cc->freepages); INIT_LIST_HEAD(&cc->migratepages); - /* - * When called via /proc/sys/vm/compact_memory - * this makes sure we compact the whole zone regardless of - * cached scanner positions. - */ - if (is_via_compact_memory(cc->order)) - __reset_isolation_suitable(zone); - if (is_via_compact_memory(cc->order) || !compaction_deferred(zone, cc->order)) compact_zone(zone, cc); @@ -1790,6 +1788,7 @@ static void compact_node(int nid) .order = -1, .mode = MIGRATE_SYNC, .ignore_skip_hint = true, + .whole_zone = true, }; __compact_pgdat(NODE_DATA(nid), &cc); diff --git a/mm/internal.h b/mm/internal.h index 1501304f87a4..5214bf8e3171 100644 --- a/mm/internal.h +++ b/mm/internal.h @@ -179,7 +179,7 @@ struct compact_control { enum migrate_mode mode; /* Async or sync migration mode */ bool ignore_skip_hint; /* Scan blocks even if marked skip */ bool direct_compaction; /* False from kcompactd or /proc/... */ - bool whole_zone; /* Whole zone has been scanned */ + bool whole_zone; /* Whole zone should/has been scanned */ int order; /* order a direct compactor needs */ const gfp_t gfp_mask; /* gfp mask of a direct compactor */ const unsigned int alloc_flags; /* alloc flags of a direct compactor */ -- 2.20.1