linux-kernel - Re: [patch 1/4] mm: vmscan: remove remains of kswapd-managed zone->all

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Date:	Mon, 23 Jun 2014 09:49:00 +0200
From:	Michal Hocko <mhocko@...e.cz>
To:	Johannes Weiner <hannes@...xchg.org>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Mel Gorman <mgorman@...e.de>, Rik van Riel <riel@...hat.com>,
	linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [patch 1/4] mm: vmscan: remove remains of kswapd-managed
 zone->all_unreclaimable

On Fri 20-06-14 12:33:47, Johannes Weiner wrote:
> shrink_zones() has a special branch to skip the all_unreclaimable()
> check during hibernation, because a frozen kswapd can't mark a zone
> unreclaimable.
> 
> But ever since 6e543d5780e3 ("mm: vmscan: fix do_try_to_free_pages()
> livelock"), determining a zone to be unreclaimable is done by directly
> looking at its scan history and no longer relies on kswapd setting the
> per-zone flag.
> 
> Remove this branch and let shrink_zones() check the reclaimability of
> the target zones regardless of hibernation state.
> 
> Signed-off-by: Johannes Weiner <hannes@...xchg.org>

This code is really tricky :/

But the patch looks good to me.
Acked-by: Michal Hocko <mhocko@...e.cz>

> ---
>  mm/vmscan.c | 8 --------
>  1 file changed, 8 deletions(-)
> 
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index 0f16ffe8eb67..19b5b8016209 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -2534,14 +2534,6 @@ out:
>  	if (sc->nr_reclaimed)
>  		return sc->nr_reclaimed;
>  
> -	/*
> -	 * As hibernation is going on, kswapd is freezed so that it can't mark
> -	 * the zone into all_unreclaimable. Thus bypassing all_unreclaimable
> -	 * check.
> -	 */
> -	if (oom_killer_disabled)
> -		return 0;
> -
>  	/* Aborted reclaim to try compaction? don't OOM, then */
>  	if (aborted_reclaim)
>  		return 1;
> -- 
> 2.0.0
> 

-- 
Michal Hocko
SUSE Labs
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