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>

1 files changed, 7 insertions, 7 deletions

diff --git a/mm/vmscan.c b/mm/vmscan.c
index db5722a07d4f..039f08d369a5 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -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;
 }