linux-kernel - Re: [PATCH] mm: memcg: keep root group unchanged if fail to create new

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Date:	Mon, 12 Dec 2011 14:11:18 +0100
From:	Michal Hocko <mhocko@...e.cz>
To:	Hillf Danton <dhillf@...il.com>
Cc:	Hugh Dickins <hughd@...gle.com>,
	Balbir Singh <bsingharora@...il.com>,
	David Rientjes <rientjes@...gle.com>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Johannes Weiner <hannes@...xchg.org>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	linux-mm@...ck.org, LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] mm: memcg: keep root group unchanged if fail to create
 new

On Sun 11-12-11 15:39:43, Hugh Dickins wrote:
> On Sun, 11 Dec 2011, Hillf Danton wrote:
> 
> > If the request is not to create root group and we fail to meet it,
> > we'd leave the root unchanged.
> 
> I didn't understand that at first: please say "we should" rather
> than "we'd", which I take to be an abbreviation for "we would".
> 
> > 
> > Signed-off-by: Hillf Danton <dhillf@...il.com>
> 
> Yes indeed, well caught:
> Acked-by: Hugh Dickins <hughd@...gle.com>
> 
> I wonder what was going through the author's mind when he wrote it
> that way?  I wonder if it's one of those bugs that creeps in when
> you start from a perfectly functional patch, then make refinements
> to suit feedback from reviewers.
> 
> On which topic: wouldn't this patch be better just to move the
> "root_mem_cgroup = memcg;" two lines lower down (and of course
> remove free_out's "root_mem_cgroup = NULL;" as you already did)?

Yes would look nicer.

> I can't see mem_cgroup_soft_limit_tree_init() relying on
> root_mem_cgroup at all.

It doesn't but it still needs some love to handle error case properly
AFAICS. We do not deallocate softlimit trees for nodes that succeeded.

[...]

Hilf could you update the patch please?
-- 
Michal Hocko
SUSE Labs
SUSE LINUX s.r.o.
Lihovarska 1060/12
190 00 Praha 9    
Czech Republic
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