linux-kernel - Re: [resend][PATCH] mm, vmscan: fix do_try_to_free

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Date:	Thu, 14 Jun 2012 17:51:49 +0900
From:	Kamezawa Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To:	kosaki.motohiro@...il.com
CC:	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	akpm@...ux-foundation.org,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Nick Piggin <npiggin@...il.com>, Michal Hocko <mhocko@...e.cz>,
	Johannes Weiner <hannes@...xchg.org>,
	Mel Gorman <mel@....ul.ie>, Minchan Kim <minchan.kim@...il.com>
Subject: Re: [resend][PATCH] mm, vmscan: fix do_try_to_free_pages() livelock

(2012/06/14 17:13), kosaki.motohiro@...il.com wrote:
> From: KOSAKI Motohiro<kosaki.motohiro@...fujitsu.com>
> 
> Currently, do_try_to_free_pages() can enter livelock. Because of,
> now vmscan has two conflicted policies.
> 
> 1) kswapd sleep when it couldn't reclaim any page when reaching
>     priority 0. This is because to avoid kswapd() infinite
>     loop. That said, kswapd assume direct reclaim makes enough
>     free pages to use either regular page reclaim or oom-killer.
>     This logic makes kswapd ->  direct-reclaim dependency.
> 2) direct reclaim continue to reclaim without oom-killer until
>     kswapd turn on zone->all_unreclaimble. This is because
>     to avoid too early oom-kill.
>     This logic makes direct-reclaim ->  kswapd dependency.
> 
> In worst case, direct-reclaim may continue to page reclaim forever
> when kswapd sleeps forever.
> 
> We can't turn on zone->all_unreclaimable from direct reclaim path
> because direct reclaim path don't take any lock and this way is racy.
> 
> Thus this patch removes zone->all_unreclaimable field completely and
> recalculates zone reclaimable state every time.
> 
> Note: we can't take the idea that direct-reclaim see zone->pages_scanned
> directly and kswapd continue to use zone->all_unreclaimable. Because, it
> is racy. commit 929bea7c71 (vmscan: all_unreclaimable() use
> zone->all_unreclaimable as a name) describes the detail.
> 
> Reported-by: Aaditya Kumar<aaditya.kumar.30@...il.com>
> Reported-by: Ying Han<yinghan@...gle.com>
> Cc: Nick Piggin<npiggin@...il.com>
> Acked-by: Rik van Riel<riel@...hat.com>
> Cc: Michal Hocko<mhocko@...e.cz>
> Cc: Johannes Weiner<hannes@...xchg.org>
> Cc: Mel Gorman<mel@....ul.ie>
> Cc: KAMEZAWA Hiroyuki<kamezawa.hiroyu@...fujitsu.com>
> Cc: Minchan Kim<minchan.kim@...il.com>
> Signed-off-by: KOSAKI Motohiro<kosaki.motohiro@...fujitsu.com>

I like this.
Acked-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>

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