>
> From: Michal Hocko <mhocko@xxxxxxxx>
>
> 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.
>
> Suggested-by: David Rientjes <rientjes@xxxxxxxxxx>
> Signed-off-by: Michal Hocko <mhocko@xxxxxxxx>
> ---
Acked-by: Hillf Danton <hillf.zj@xxxxxxxxxxxxxxx>
> mm/vmscan.c | 14 +++++++-------
> 1 file changed, 7 insertions(+), 7 deletions(-)
>
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index 489212252cd6..9145e3f89eab 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -196,21 +196,21 @@ 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;
> }
>
> --
> 2.7.0.rc3
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