From 0bf1457f0cfca7bc026a82323ad34bcf58ad035d Mon Sep 17 00:00:00 2001 From: Johannes Weiner Date: Tue, 8 Apr 2014 16:04:10 -0700 Subject: [PATCH] mm: vmscan: do not swap anon pages just because free+file is low Page reclaim force-scans / swaps anonymous pages when file cache drops below the high watermark of a zone in order to prevent what little cache remains from thrashing. However, on bigger machines the high watermark value can be quite large and when the workload is dominated by a static anonymous/shmem set, the file set might just be a small window of used-once cache. In such situations, the VM starts swapping heavily when instead it should be recycling the no longer used cache. This is a longer-standing problem, but it's more likely to trigger after commit 81c0a2bb515f ("mm: page_alloc: fair zone allocator policy") because file pages can no longer accumulate in a single zone and are dispersed into smaller fractions among the available zones. To resolve this, do not force scan anon when file pages are low but instead rely on the scan/rotation ratios to make the right prediction. Signed-off-by: Johannes Weiner Acked-by: Rafael Aquini Cc: Rik van Riel Cc: Mel Gorman Cc: Hugh Dickins Cc: Suleiman Souhlal Cc: [3.12+] Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- mm/vmscan.c | 16 +--------------- 1 file changed, 1 insertion(+), 15 deletions(-) diff --git a/mm/vmscan.c b/mm/vmscan.c index 06879ead7380..9b6497eda806 100644 --- a/mm/vmscan.c +++ b/mm/vmscan.c @@ -1862,7 +1862,7 @@ static void get_scan_count(struct lruvec *lruvec, struct scan_control *sc, struct zone *zone = lruvec_zone(lruvec); unsigned long anon_prio, file_prio; enum scan_balance scan_balance; - unsigned long anon, file, free; + unsigned long anon, file; bool force_scan = false; unsigned long ap, fp; enum lru_list lru; @@ -1915,20 +1915,6 @@ static void get_scan_count(struct lruvec *lruvec, struct scan_control *sc, file = get_lru_size(lruvec, LRU_ACTIVE_FILE) + get_lru_size(lruvec, LRU_INACTIVE_FILE); - /* - * If it's foreseeable that reclaiming the file cache won't be - * enough to get the zone back into a desirable shape, we have - * to swap. Better start now and leave the - probably heavily - * thrashing - remaining file pages alone. - */ - if (global_reclaim(sc)) { - free = zone_page_state(zone, NR_FREE_PAGES); - if (unlikely(file + free <= high_wmark_pages(zone))) { - scan_balance = SCAN_ANON; - goto out; - } - } - /* * There is enough inactive page cache, do not reclaim * anything from the anonymous working set right now. -- 2.39.5