linux-kernel - Re: [PATCH for 3.2.34] memcg: do not trigger OOM from add_to_page_cache

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Message-ID: <20121228163521.GB1455@dhcp22.suse.cz>
Date:	Fri, 28 Dec 2012 17:35:21 +0100
From:	Michal Hocko <mhocko@...e.cz>
To:	azurIt <azurit@...ox.sk>
Cc:	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	cgroups mailinglist <cgroups@...r.kernel.org>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Johannes Weiner <hannes@...xchg.org>
Subject: Re: [PATCH for 3.2.34] memcg: do not trigger OOM from
 add_to_page_cache_locked

On Mon 24-12-12 14:38:50, azurIt wrote:
> >OK, good to hear and fingers crossed. I will try to get back to the
> >original problem and a better solution sometimes early next year when
> >all the things settle a bit.
> 
> 
> Btw, i noticed one more thing when problem is happening (=when any
> cgroup is stucked), i fogot to mention it before, sorry :( . It's
> related to HDDs, something is slowing them down in a strange way. All
> services are working normally and i really cannot notice any slowness,
> the only thing which i noticed is affeceted is our backup software (
> www.Bacula.org ). When problem occurs at night, so it's happening when
> backup is running, backup is extremely slow and usually don't finish
> until i kill processes inside affected cgroup (=until i resolve the
> problem). Backup software is NOT doing big HDD bandwidth BUT it's
> doing quite huge number of disk operations (it needs to stat every
> file and directory). I believe that only speed of disk operations are
> affected and are very slow.

I would bet that this is caused by the blocked proceses in memcg oom
handler which hold i_mutex and the backup process wants to access the
same inode with an operation which requires the lock.
-- 
Michal Hocko
SUSE Labs
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