linux-kernel - Re: [PATCH RFC 3/3] mm, vmscan: correct prepare_kswapd

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Date:   Tue, 24 Jan 2017 17:01:07 -0500
From:   Rik van Riel <riel@...hat.com>
To:     Jia He <hejianet@...il.com>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Naoya Horiguchi <n-horiguchi@...jp.nec.com>,
        Michal Hocko <mhocko@...e.com>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        "Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>,
        Gerald Schaefer <gerald.schaefer@...ibm.com>,
        zhong jiang <zhongjiang@...wei.com>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Vaishali Thakkar <vaishali.thakkar@...cle.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Mel Gorman <mgorman@...hsingularity.net>,
        Vlastimil Babka <vbabka@...e.cz>,
        Minchan Kim <minchan@...nel.org>
Subject: Re: [PATCH RFC 3/3] mm, vmscan: correct prepare_kswapd_sleep return
 value

On Tue, 2017-01-24 at 15:49 +0800, Jia He wrote:
> When there is no reclaimable pages in the zone, even the zone is
> not balanced, we let kswapd go sleeping. That is prepare_kswapd_sleep
> will return true in this case.
> 
> Signed-off-by: Jia He <hejianet@...il.com>
> ---
>  mm/vmscan.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index 7396a0a..54445e2 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -3140,7 +3140,8 @@ static bool prepare_kswapd_sleep(pg_data_t
> *pgdat, int order, int classzone_idx)
>  		if (!managed_zone(zone))
>  			continue;
>  
> -		if (!zone_balanced(zone, order, classzone_idx))
> +		if (!zone_balanced(zone, order, classzone_idx)
> +			&& !zone_reclaimable_pages(zone))
>  			return false;
>  	}

This patch does the opposite of what your changelog
says.  The above keeps kswapd running forever if
the zone is not balanced, and there are no reclaimable
pages.