Re: [PATCH 2/9] mm: fix check for reclaimable pages in PF_MEMALLOC reclaim throttling

[Michal Hocko]

On Tue 28-02-17 16:40:00, Johannes Weiner wrote:
> PF_MEMALLOC direct reclaimers get throttled on a node when the sum of
> all free pages in each zone fall below half the min watermark. During
> the summation, we want to exclude zones that don't have reclaimables.
> Checking the same pgdat over and over again doesn't make sense.
> 
> Fixes: 599d0c954f91 ("mm, vmscan: move LRU lists to node")
> Signed-off-by: Johannes Weiner <hannes@xxxxxxxxxxx>

Acked-by: Michal Hocko <mhocko@xxxxxxxx>

> ---
>  mm/vmscan.c | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index 407b27831ff7..f006140f58c6 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -2838,8 +2838,10 @@ static bool pfmemalloc_watermark_ok(pg_data_t *pgdat)
>  
>  	for (i = 0; i <= ZONE_NORMAL; i++) {
>  		zone = &pgdat->node_zones[i];
> -		if (!managed_zone(zone) ||
> -		    pgdat_reclaimable_pages(pgdat) == 0)
> +		if (!managed_zone(zone))
> +			continue;
> +
> +		if (!zone_reclaimable_pages(zone))
>  			continue;
>  
>  		pfmemalloc_reserve += min_wmark_pages(zone);
> -- 
> 2.11.1

-- 
Michal Hocko
SUSE Labs