Commit 0db2cb8d authored Mar 15, 2016 by Michal Hocko Committed by Linus Torvalds Mar 15, 2016

mm, vmscan: make zone_reclaimable_pages more precise



zone_reclaimable_pages() is used in should_reclaim_retry() which uses it
to calculate the target for the watermark check.  This means that
precise numbers are important for the correct decision.
zone_reclaimable_pages uses zone_page_state which can contain stale data
with per-cpu diffs not synced yet (the last vmstat_update might have run
1s in the past).

Use zone_page_state_snapshot() in zone_reclaimable_pages() instead.
None of the current callers is in a hot path where getting the precise
value (which involves per-cpu iteration) would cause an unreasonable
overhead.

Signed-off-by: Michal Hocko <mhocko@suse.com>
Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Suggested-by: David Rientjes <rientjes@google.com>
Acked-by: David Rientjes <rientjes@google.com>
Acked-by: Hillf Danton <hillf.zj@alibaba-inc.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

parent d7206a70

mm/vmscan.c

+7 −7

Original line number	Diff line number	Diff line
		@@ -195,21 +195,21 @@ static unsigned long zone_reclaimable_pages(struct zone *zone)
		{
		unsigned long nr;

		nr = zone_page_state(zone, NR_ACTIVE_FILE) +
		zone_page_state(zone, NR_INACTIVE_FILE) +
		zone_page_state(zone, NR_ISOLATED_FILE);
		nr = zone_page_state_snapshot(zone, NR_ACTIVE_FILE) +
		zone_page_state_snapshot(zone, NR_INACTIVE_FILE) +
		zone_page_state_snapshot(zone, NR_ISOLATED_FILE);

		if (get_nr_swap_pages() > 0)
		nr += zone_page_state(zone, NR_ACTIVE_ANON) +
		zone_page_state(zone, NR_INACTIVE_ANON) +
		zone_page_state(zone, NR_ISOLATED_ANON);
		nr += zone_page_state_snapshot(zone, NR_ACTIVE_ANON) +
		zone_page_state_snapshot(zone, NR_INACTIVE_ANON) +
		zone_page_state_snapshot(zone, NR_ISOLATED_ANON);

		return nr;
		}

		bool zone_reclaimable(struct zone *zone)
		{
		return zone_page_state(zone, NR_PAGES_SCANNED) <
		return zone_page_state_snapshot(zone, NR_PAGES_SCANNED) <
		zone_reclaimable_pages(zone) * 6;
		}

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