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From: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
To: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Subject: Re: [PATCH 1/5] vmscan: remove all_unreclaimable check from direct reclaim path completely
Cc: kosaki.motohiro@jp.fujitsu.com, linux-kernel@vger.kernel.org,
        Andrew Morton <akpm@linux-foundation.org>,
        David Rientjes <rientjes@google.com>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Rik van Riel <riel@redhat.com>, Oleg Nesterov <oleg@redhat.com>,
        linux-mm <linux-mm@kvack.org>, Andrey Vagin <avagin@openvz.org>,
        Hugh Dickins <hughd@google.com>, Nick Piggin <npiggin@kernel.dk>,
        Minchan Kim <minchan.kim@gmail.com>,
        Johannes Weiner <hannes@cmpxchg.org>
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Date: Wed, 23 Mar 2011 16:55:12 +0900 (JST)
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> > Reported-by: Andrey Vagin <avagin@openvz.org>
> > Cc: Nick Piggin <npiggin@kernel.dk>
> > Cc: Minchan Kim <minchan.kim@gmail.com>
> > Cc: Johannes Weiner <hannes@cmpxchg.org>
> > Cc: Rik van Riel <riel@redhat.com>
> > Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
> > Signed-off-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
> 
> IIUC, I saw the pehnomenon which you pointed out, as
>  - all zone->all_unreclaimable = yes
>  - zone_reclaimable() returns true
>  - no pgscan proceeds.
> 
> on a swapless system. So, I'd like to vote for this patch.
> 
> But hmm...what happens all of pages are isolated or locked and now under freeing ?
> I think we should have alternative safe-guard logic for avoiding to call
> oom-killer. Hmm.

Yes, this patch has small risk. but 1) this logic didn't work about two
years (see changelog) 2) memcg haven't use this logic and I haven't get
any bug report from memcg developers. therefore I decided to take most
simple way.

Of cource, I'll make another protection if I'll get any regression report.