linux-kernel - Re: [PATCH 3/9] mm: remove seemingly spurious reclaimability check from laptop

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Message-ID: <20170301150620.GC11730@dhcp22.suse.cz>
Date:   Wed, 1 Mar 2017 16:06:21 +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 3/9] mm: remove seemingly spurious reclaimability check
 from laptop_mode gating

On Tue 28-02-17 16:40:01, Johannes Weiner wrote:
> 1d82de618ddd ("mm, vmscan: make kswapd reclaim in terms of nodes")
> allowed laptop_mode=1 to start writing not just when the priority
> drops to DEF_PRIORITY - 2 but also when the node is unreclaimable.
> That appears to be a spurious change in this patch as I doubt the
> series was tested with laptop_mode, and neither is that particular
> change mentioned in the changelog. Remove it, it's still recent.

The less pgdat_reclaimable we have the better IMHO. If this is really
needed then I would appreciate a proper explanation because each such
a heuristic is just a head scratcher - especially after few years when
all the details are long forgotten.

> Signed-off-by: Johannes Weiner <hannes@...xchg.org>

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

> ---
>  mm/vmscan.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index f006140f58c6..911957b66622 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -3288,7 +3288,7 @@ static int balance_pgdat(pg_data_t *pgdat, int order, int classzone_idx)
>  		 * If we're getting trouble reclaiming, start doing writepage
>  		 * even in laptop mode.
>  		 */
> -		if (sc.priority < DEF_PRIORITY - 2 || !pgdat_reclaimable(pgdat))
> +		if (sc.priority < DEF_PRIORITY - 2)
>  			sc.may_writepage = 1;
>  
>  		/* Call soft limit reclaim before calling shrink_node. */
> -- 
> 2.11.1

-- 
Michal Hocko
SUSE Labs