Compaction should finish when the migration and free scanner meet, i.e. they reach the same pageblock. Currently however, the test in compact_finished() simply just compares the exact pfns, which may yield a false negative when the free scanner position is in the middle of a pageblock and the migration scanner reaches the begining of the same pageblock. This hasn't been a problem until commit e14c720efdd7 ("mm, compaction: remember position within pageblock in free pages scanner") allowed the free scanner position to be in the middle of a pageblock between invocations. The hot-fix 1d5bfe1ffb5b ("mm, compaction: prevent infinite loop in compact_zone") prevented the issue by adding a special check in the migration scanner to satisfy the current detection of scanners meeting. However, the proper fix is to make the detection more robust. This patch introduces the compact_scanners_met() function that returns true when the free scanner position is in the same or lower pageblock than the migration scanner. The special case in isolate_migratepages() introduced by 1d5bfe1ffb5b is removed. Suggested-by: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx> Signed-off-by: Vlastimil Babka <vbabka@xxxxxxx> Cc: Minchan Kim <minchan@xxxxxxxxxx> Acked-by: Mel Gorman <mgorman@xxxxxxx> Acked-by: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx> Acked-by: Michal Nazarewicz <mina86@xxxxxxxxxx> Cc: Naoya Horiguchi <n-horiguchi@xxxxxxxxxxxxx> Cc: Christoph Lameter <cl@xxxxxxxxx> Acked-by: Rik van Riel <riel@xxxxxxxxxx> Cc: David Rientjes <rientjes@xxxxxxxxxx> --- mm/compaction.c | 22 ++++++++++++++-------- 1 file changed, 14 insertions(+), 8 deletions(-) diff --git a/mm/compaction.c b/mm/compaction.c index 16e1b57..d46aaeb 100644 --- a/mm/compaction.c +++ b/mm/compaction.c @@ -902,6 +902,16 @@ static bool suitable_migration_target(struct page *page) } /* + * Test whether the free scanner has reached the same or lower pageblock than + * the migration scanner, and compaction should thus terminate. + */ +static inline bool compact_scanners_met(struct compact_control *cc) +{ + return (cc->free_pfn >> pageblock_order) + <= (cc->migrate_pfn >> pageblock_order); +} + +/* * Based on information in the current compact_control, find blocks * suitable for isolating free pages from and then isolate them. */ @@ -1131,12 +1141,8 @@ static isolate_migrate_t isolate_migratepages(struct zone *zone, } acct_isolated(zone, cc); - /* - * Record where migration scanner will be restarted. If we end up in - * the same pageblock as the free scanner, make the scanners fully - * meet so that compact_finished() terminates compaction. - */ - cc->migrate_pfn = (end_pfn <= cc->free_pfn) ? low_pfn : cc->free_pfn; + /* Record where migration scanner will be restarted. */ + cc->migrate_pfn = low_pfn; return cc->nr_migratepages ? ISOLATE_SUCCESS : ISOLATE_NONE; } @@ -1151,7 +1157,7 @@ static int __compact_finished(struct zone *zone, struct compact_control *cc, return COMPACT_PARTIAL; /* Compaction run completes if the migrate and free scanner meet */ - if (cc->free_pfn <= cc->migrate_pfn) { + if (compact_scanners_met(cc)) { /* Let the next compaction start anew. */ zone->compact_cached_migrate_pfn[0] = zone->zone_start_pfn; zone->compact_cached_migrate_pfn[1] = zone->zone_start_pfn; @@ -1380,7 +1386,7 @@ static int compact_zone(struct zone *zone, struct compact_control *cc) * migrate_pages() may return -ENOMEM when scanners meet * and we want compact_finished() to detect it */ - if (err == -ENOMEM && cc->free_pfn > cc->migrate_pfn) { + if (err == -ENOMEM && !compact_scanners_met(cc)) { ret = COMPACT_PARTIAL; goto out; } -- 2.4.6 -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx"> email@xxxxxxxxx </a>