Date: Wed, 15 Aug 2012 15:26:21 +0200
From: Michal Hocko <mhocko@suse.cz>
To: Glauber Costa <glommer@parallels.com>
Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, cgroups@vger.kernel.org,
        devel@openvz.org, Johannes Weiner <hannes@cmpxchg.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        kamezawa.hiroyu@jp.fujitsu.com, Christoph Lameter <cl@linux.com>,
        David Rientjes <rientjes@google.com>,
        Pekka Enberg <penberg@kernel.org>
Subject: Re: [PATCH v2 04/11] kmem accounting basic infrastructure
Message-ID: <20120815132621.GJ23985@dhcp22.suse.cz>
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 <1344517279-30646-5-git-send-email-glommer@parallels.com>
 <20120814162144.GC6905@dhcp22.suse.cz>
 <502B6D03.1080804@parallels.com>
 <20120815123931.GF23985@dhcp22.suse.cz>
 <502B9BD4.4070003@parallels.com>
 <20120815130228.GH23985@dhcp22.suse.cz>
 <502B9E5F.2080907@parallels.com>
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On Wed 15-08-12 17:04:31, Glauber Costa wrote:
> On 08/15/2012 05:02 PM, Michal Hocko wrote:
> > On Wed 15-08-12 16:53:40, Glauber Costa wrote:
> > [...]
> >>>>> This doesn't check for the hierachy so kmem_accounted might not be in 
> >>>>> sync with it's parents. mem_cgroup_create (below) needs to copy
> >>>>> kmem_accounted down from the parent and the above needs to check if this
> >>>>> is a similar dance like mem_cgroup_oom_control_write.
> >>>>>
> >>>>
> >>>> I don't see why we have to.
> >>>>
> >>>> I believe in a A/B/C hierarchy, C should be perfectly able to set a
> >>>> different limit than its parents. Note that this is not a boolean.
> >>>
> >>> Ohh, I wasn't clear enough. I am not against setting the _limit_ I just
> >>> meant that the kmem_accounted should be consistent within the hierarchy.
> >>>
> >>
> >> If a parent of yours is accounted, you get accounted as well. This is
> >> not the state in this patch, but gets added later. Isn't this enough ?
> > 
> > But if the parent is not accounted, you can set the children to be
> > accounted, right? Or maybe this is changed later in the series? I didn't
> > get to the end yet.
> > 
> 
> Yes, you can. Do you see any problem with that?

Well, if a child contributes with the kmem charges upwards the hierachy
then a parent can have kmem.usage > 0 with disabled accounting.
I am not saying this is a no-go but it definitely is confusing and I do
not see any good reason for it. I've considered it as an overlook rather
than a deliberate design decision.
-- 
Michal Hocko
SUSE Labs
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