linux-kernel - Re: [PATCH 0/2] memcg: mm_update_next

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Message-ID: <20140422105228.GJ29311@dhcp22.suse.cz>
Date:	Tue, 22 Apr 2014 12:52:29 +0200
From:	Michal Hocko <mhocko@...e.cz>
To:	Oleg Nesterov <oleg@...hat.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Peter Chiang <pchiang@...dia.com>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Balbir Singh <bsingharora@...il.com>,
	Johannes Weiner <hannes@...xchg.org>,
	"ccross@...roid.com" <ccross@...roid.com>,
	"lizefan@...wei.com" <lizefan@...wei.com>,
	"tj@...nel.org" <tj@...nel.org>, "pavel@....cz" <pavel@....cz>,
	"ebiederm@...ssion.com" <ebiederm@...ssion.com>,
	"guillaume@...infr.org" <guillaume@...infr.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 0/2] memcg: mm_update_next_owner() should skip kthreads

On Fri 18-04-14 20:44:41, Oleg Nesterov wrote:
> On 04/18, Michal Hocko wrote:
> >
> > On Fri 18-04-14 19:26:31, Oleg Nesterov wrote:
> > > On 04/18, Oleg Nesterov wrote:
> > > >
> > > > Hmm. I seem to see a bug in this function, it can be fulled by use_mm,
> > > > but I am not sure this can explain the problem. I'll send a patch.
> > >
> > > Untested, please review. But it really looks "obviously wrong", and note
> > > that unuse_mm() doesn't do mm_update_next_owner(). (just in case, do not
> > > confuse it with unuse_mm() in mm/swapfile.c).
> >
> > Both patches seem to be correct but I am missinng why they are marked as
> > memcg: when they are touching generic mm_update_next_owner path.
> 
> Well, this is because I didn't know which prefix should I use. I looked
> at git-blame to see who changed this function, picked the random 733eda7ac
> "memcg: clear mm->owner when last possible owner leaves" commit and copied
> "memcg" from there.
> 
> OTOH, mm->owner is used by mm/memcontrol.c, so perhaps the prefix is fine?

OK, I didn't realize memcg is the only user.

> I do not even understand why do we have CONFIG_MM_OWNER, perhaps it should
> die?

I have to dig into history to check why it has been introduced in the
first place. It might be possible it is not relevant anymore.
-- 
Michal Hocko
SUSE Labs
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