memcg, vmscan: Fix forced scan of anonymous pages (2ab051e1) · Commits · 戴 / test

When memory cgoups are enabled, the code that decides to force to scan anonymous pages in get_scan_count() compares global values (free, high_watermark) to a value that is restricted to a memory cgroup (file). It make the code over-eager to force anon scan. For instance, it will force anon scan when scanning a memcg that is mainly populated by anonymous page, even when there is plenty of file pages to get rid of in others memcgs, even when swappiness == 0. It breaks user's expectation about swappiness and hurts performance. This patch makes sure that forced anon scan only happens when there not enough file pages for the all zone, not just in one random memcg. [hannes@cmpxchg.org: cleanups] Signed-off-by:

Jerome Marchand <jmarchan@redhat.com> Acked-by:

Michal Hocko <mhocko@suse.cz> Acked-by:

Johannes Weiner <hannes@cmpxchg.org> Reviewed-by:

Rik van Riel <riel@redhat.com> Cc: Mel Gorman <mgorman@suse.de> Signed-off-by:

Johannes Weiner <hannes@cmpxchg.org> Signed-off-by:

Andrew Morton <akpm@linux-foundation.org> Signed-off-by:

Linus Torvalds <torvalds@linux-foundation.org>

mm/vmscan.c

+13 −7

Original line number	Diff line number	Diff line
		@@ -1930,11 +1930,6 @@ static void get_scan_count(struct lruvec *lruvec, int swappiness,
		goto out;
		}

		anon = get_lru_size(lruvec, LRU_ACTIVE_ANON) +
		get_lru_size(lruvec, LRU_INACTIVE_ANON);
		file = get_lru_size(lruvec, LRU_ACTIVE_FILE) +
		get_lru_size(lruvec, LRU_INACTIVE_FILE);

		/*
		* Prevent the reclaimer from falling into the cache trap: as
		* cache pages start out inactive, every cache fault will tip
		@@ -1945,9 +1940,14 @@ static void get_scan_count(struct lruvec *lruvec, int swappiness,
		* anon pages. Try to detect this based on file LRU size.
		*/
		if (global_reclaim(sc)) {
		unsigned long free = zone_page_state(zone, NR_FREE_PAGES);
		unsigned long zonefile;
		unsigned long zonefree;

		zonefree = zone_page_state(zone, NR_FREE_PAGES);
		zonefile = zone_page_state(zone, NR_ACTIVE_FILE) +
		zone_page_state(zone, NR_INACTIVE_FILE);

		if (unlikely(file + free <= high_wmark_pages(zone))) {
		if (unlikely(zonefile + zonefree <= high_wmark_pages(zone))) {
		scan_balance = SCAN_ANON;
		goto out;
		}
		@@ -1982,6 +1982,12 @@ static void get_scan_count(struct lruvec *lruvec, int swappiness,
		*
		* anon in [0], file in [1]
		*/

		anon = get_lru_size(lruvec, LRU_ACTIVE_ANON) +
		get_lru_size(lruvec, LRU_INACTIVE_ANON);
		file = get_lru_size(lruvec, LRU_ACTIVE_FILE) +
		get_lru_size(lruvec, LRU_INACTIVE_FILE);

		spin_lock_irq(&zone->lru_lock);
		if (unlikely(reclaim_stat->recent_scanned[0] > anon / 4)) {
		reclaim_stat->recent_scanned[0] /= 2;

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