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Date: Fri, 22 Mar 2013 13:41:40 +0400
From: Glauber Costa <glommer@parallels.com>
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To: Michal Hocko <mhocko@suse.cz>
CC: Li Zefan <lizefan@huawei.com>, Tejun Heo <tj@kernel.org>,
        LKML <linux-kernel@vger.kernel.org>, Cgroups <cgroups@vger.kernel.org>,
        <linux-mm@kvack.org>,
        KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>,
        Johannes Weiner <hannes@cmpxchg.org>
Subject: Re: [PATCH] memcg: fix memcg_cache_name() to use cgroup_name()
References: <514A60CD.60208@huawei.com> <20130321090849.GF6094@dhcp22.suse.cz> <20130321102257.GH6094@dhcp22.suse.cz> <514BB23E.70908@huawei.com> <20130322080749.GB31457@dhcp22.suse.cz> <514C1388.6090909@huawei.com> <514C14BF.3050009@parallels.com> <20130322093141.GE31457@dhcp22.suse.cz>
In-Reply-To: <20130322093141.GE31457@dhcp22.suse.cz>
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On 03/22/2013 01:31 PM, Michal Hocko wrote:
> On Fri 22-03-13 12:22:23, Glauber Costa wrote:
>> On 03/22/2013 12:17 PM, Li Zefan wrote:
>>>> GFP_TEMPORARY groups short lived allocations but the mem cache is not
>>>>> an ideal candidate of this type of allocations..
>>>>>
>>> I'm not sure I'm following you...
>>>
>>> char *memcg_cache_name()
>>> {
>>> 	char *name = alloc();
>>> 	return name;
>>> }
>>>
>>> kmem_cache_dup()
>>> {
>>> 	name = memcg_cache_name();
>>> 	kmem_cache_create_memcg(name);
>>> 	free(name);
>>> }
>>>
>>> Isn't this a short lived allocation?
>>>
>>
>> Hi,
>>
>> Thanks for identifying and fixing this.
>>
>> Li is right. The cache name will live long, but this is because the
>> slab/slub caches will strdup it internally. So the actual memcg
>> allocation is short lived.
> 
> OK, I have totally missed that. Sorry about the confusion. Then all the
> churn around the allocation is pointless, no?
> What about:

If we're really not concerned about stack, then yes. Even if always
running from workqueues, a PAGE_SIZEd stack variable seems risky to me.