linux-kernel - Re: [PATCH -mm] memcg: prevent from OOM with too many dirty pages

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Message-ID: <20120620095546.GB8765@localhost>
Date:	Wed, 20 Jun 2012 17:55:46 +0800
From:	Fengguang Wu <fengguang.wu@...el.com>
To:	Mel Gorman <mgorman@...e.de>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Michal Hocko <mhocko@...e.cz>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujtisu.com>,
	Minchan Kim <minchan@...nel.org>,
	Rik van Riel <riel@...hat.com>,
	Ying Han <yinghan@...gle.com>,
	Greg Thelen <gthelen@...gle.com>,
	Hugh Dickins <hughd@...gle.com>,
	Johannes Weiner <hannes@...xchg.org>
Subject: Re: [PATCH -mm] memcg: prevent from OOM with too many dirty pages

> > Finally, I wonder if there should be some timeout of that wait.  I
> > don't know why, but I wouldn't be surprised if we hit some glitch which
> > causes us to add one!
> > 
> 
> If we hit such a situation it means that flush is no longer working which
> is interesting in itself. I guess one possibility where it can occur is
> if we hit global dirty limits (or memcg dirty limits when they exist)
> and the page is backed by NFS that is disconnected. That would stall here
> potentially forever but it's already the case that a system that hits its
> dirty limits with a disconnected NFS is in trouble and a timeout here will
> not do much to help.

Agreed. I've run into such cases and cannot login even locally because
the shell will be blocked trying to write even 1 byte at startup time. 
Any opened shells are also stalled on writing to .bash_history etc.

Thanks,
Fengguang
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