linux-kernel - Re: [PATCH 2/9] mm: fix check for reclaimable pages in PF

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Date:   Wed, 1 Mar 2017 16:02:59 +0100
From:   Michal Hocko <mhocko@...nel.org>
To:     Johannes Weiner <hannes@...xchg.org>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Jia He <hejianet@...il.com>, Mel Gorman <mgorman@...e.de>,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        kernel-team@...com
Subject: Re: [PATCH 2/9] mm: fix check for reclaimable pages in PF_MEMALLOC
 reclaim throttling

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@...xchg.org>

Acked-by: Michal Hocko <mhocko@...e.com>

> ---
>  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