linux-kernel - Re: [PATCH 3/5] mm: vmscan: remove old flusher wakeup from direct reclaim path

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Message-ID: <20170126132147.GC7827@dhcp22.suse.cz>
Date:   Thu, 26 Jan 2017 14:21:47 +0100
From:   Michal Hocko <mhocko@...nel.org>
To:     Johannes Weiner <hannes@...xchg.org>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Mel Gorman <mgorman@...e.de>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, kernel-team@...com
Subject: Re: [PATCH 3/5] mm: vmscan: remove old flusher wakeup from direct
 reclaim path

On Mon 23-01-17 13:16:39, Johannes Weiner wrote:
> Direct reclaim has been replaced by kswapd reclaim in pretty much all
> common memory pressure situations, so this code most likely doesn't
> accomplish the described effect anymore. The previous patch wakes up
> flushers for all reclaimers when we encounter dirty pages at the tail
> end of the LRU. Remove the crufty old direct reclaim invocation.
> 
> Signed-off-by: Johannes Weiner <hannes@...xchg.org>

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

> ---
>  mm/vmscan.c | 17 -----------------
>  1 file changed, 17 deletions(-)
> 
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index 56ea8d24041f..915fc658de41 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -2757,8 +2757,6 @@ static unsigned long do_try_to_free_pages(struct zonelist *zonelist,
>  					  struct scan_control *sc)
>  {
>  	int initial_priority = sc->priority;
> -	unsigned long total_scanned = 0;
> -	unsigned long writeback_threshold;
>  retry:
>  	delayacct_freepages_start();
>  
> @@ -2771,7 +2769,6 @@ static unsigned long do_try_to_free_pages(struct zonelist *zonelist,
>  		sc->nr_scanned = 0;
>  		shrink_zones(zonelist, sc);
>  
> -		total_scanned += sc->nr_scanned;
>  		if (sc->nr_reclaimed >= sc->nr_to_reclaim)
>  			break;
>  
> @@ -2784,20 +2781,6 @@ static unsigned long do_try_to_free_pages(struct zonelist *zonelist,
>  		 */
>  		if (sc->priority < DEF_PRIORITY - 2)
>  			sc->may_writepage = 1;
> -
> -		/*
> -		 * Try to write back as many pages as we just scanned.  This
> -		 * tends to cause slow streaming writers to write data to the
> -		 * disk smoothly, at the dirtying rate, which is nice.   But
> -		 * that's undesirable in laptop mode, where we *want* lumpy
> -		 * writeout.  So in laptop mode, write out the whole world.
> -		 */
> -		writeback_threshold = sc->nr_to_reclaim + sc->nr_to_reclaim / 2;
> -		if (total_scanned > writeback_threshold) {
> -			wakeup_flusher_threads(laptop_mode ? 0 : total_scanned,
> -						WB_REASON_VMSCAN);
> -			sc->may_writepage = 1;
> -		}
>  	} while (--sc->priority >= 0);
>  
>  	delayacct_freepages_end();
> -- 
> 2.11.0
> 
> --
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-- 
Michal Hocko
SUSE Labs