Message-ID: <502DEC32.6070807@parallels.com>
Date: Fri, 17 Aug 2012 11:01:06 +0400
From: Glauber Costa <glommer@parallels.com>
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To: Michal Hocko <mhocko@suse.cz>
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>,
        Pekka Enberg <penberg@cs.helsinki.fi>,
        Suleiman Souhlal <suleiman@google.com>
Subject: Re: [PATCH v2 08/11] memcg: disable kmem code when not in use.
References: <1344517279-30646-1-git-send-email-glommer@parallels.com> <1344517279-30646-9-git-send-email-glommer@parallels.com> <20120817070241.GA18600@dhcp22.suse.cz>
In-Reply-To: <20120817070241.GA18600@dhcp22.suse.cz>
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On 08/17/2012 11:02 AM, Michal Hocko wrote:
> On Thu 09-08-12 17:01:16, Glauber Costa wrote:
>> We can use jump labels to patch the code in or out when not used.
>>
>> Because the assignment: memcg->kmem_accounted = true is done after the
>> jump labels increment, we guarantee that the root memcg will always be
>> selected until all call sites are patched (see memcg_kmem_enabled).
> 
> Not that it would be really important because kmem_accounted goes away
> in a subsequent patch but I think the wording is a bit misleading here.
> First of all there is no guanratee that kmem_accounted=true is seen
> before atomic_inc(&key->enabled) because there is no memory barrier and
> the lock serves just a leave barrier. But I do not think this is
> important at all because key->enabled is what matters here. Even if
> memcg_kmem_enabled is true we do not consider it if the key is disabled,
> right?
> 

Right.

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