From: Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx> Subject: mm, compaction: check early for huge pages encountered by the migration scanner When scanning for sources or targets, PageCompound is checked for huge pages as they can be skipped quickly but it happens relatively late after a lot of setup and checking. This patch short-cuts the check to make it earlier. It might still change when the lock is acquired but this has less overhead overall. The free scanner advances but the migration scanner does not. Typically the free scanner encounters more movable blocks that change state over the lifetime of the system and also tends to scan more aggressively as it's actively filling its portion of the physical address space with data. This could change in the future but for the moment, this worked better in practice and incurred fewer scan restarts. The impact on latency and allocation success rates is marginal but the free scan rates are reduced by 15% and system CPU usage is reduced by 3.3%. The 2-socket results are not materially different. Link: http://lkml.kernel.org/r/20190118175136.31341-15-mgorman@xxxxxxxxxxxxxxxxxxx Signed-off-by: Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx> Acked-by: Vlastimil Babka <vbabka@xxxxxxx> Cc: Andrea Arcangeli <aarcange@xxxxxxxxxx> Cc: Dan Carpenter <dan.carpenter@xxxxxxxxxx> Cc: David Rientjes <rientjes@xxxxxxxxxx> Cc: YueHaibing <yuehaibing@xxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- mm/compaction.c | 16 ++++++++++++---- 1 file changed, 12 insertions(+), 4 deletions(-) --- a/mm/compaction.c~mm-compaction-check-early-for-huge-pages-encountered-by-the-migration-scanner +++ a/mm/compaction.c @@ -1061,6 +1061,9 @@ static bool suitable_migration_source(st { int block_mt; + if (pageblock_skip_persistent(page)) + return false; + if ((cc->mode != MIGRATE_ASYNC) || !cc->direct_compaction) return true; @@ -1697,12 +1700,17 @@ static isolate_migrate_t isolate_migrate continue; /* - * For async compaction, also only scan in MOVABLE blocks. - * Async compaction is optimistic to see if the minimum amount - * of work satisfies the allocation. + * For async compaction, also only scan in MOVABLE blocks + * without huge pages. Async compaction is optimistic to see + * if the minimum amount of work satisfies the allocation. + * The cached PFN is updated as it's possible that all + * remaining blocks between source and target are unsuitable + * and the compaction scanners fail to meet. */ - if (!suitable_migration_source(cc, page)) + if (!suitable_migration_source(cc, page)) { + update_cached_migrate(cc, block_end_pfn); continue; + } /* Perform the isolation */ low_pfn = isolate_migratepages_block(cc, low_pfn, _
