linux-kernel - Re: [PATCH] memcg: fix memcg_cache_name() to use cgroup

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Date:	Wed, 27 Mar 2013 19:19:58 +0400
From:	Glauber Costa <glommer@...allels.com>
To:	Michal Hocko <mhocko@...e.cz>
CC:	Johannes Weiner <hannes@...xchg.org>, Tejun Heo <tj@...nel.org>,
	Li Zefan <lizefan@...wei.com>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	<linux-mm@...ck.org>, <cgroups@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] memcg: fix memcg_cache_name() to use cgroup_name()

On 03/27/2013 07:11 PM, Michal Hocko wrote:
> On Wed 27-03-13 10:58:25, Johannes Weiner wrote:
>> On Wed, Mar 27, 2013 at 09:36:39AM +0100, Michal Hocko wrote:
> [...]
>>> +	/*
>>> +	 * kmem_cache_create_memcg duplicates the given name and
>>> +	 * cgroup_name for this name requires RCU context.
>>> +	 * This static temporary buffer is used to prevent from
>>> +	 * pointless shortliving allocation.
>>> +	 */
>>> +	if (!tmp_name) {
>>> +		tmp_name = kmalloc(PAGE_SIZE, GFP_KERNEL);
>>> +		WARN_ON_ONCE(!tmp_name);
>>
>> Just use the page allocator directly and get a free allocation failure
>> warning. 
> 
> WARN_ON_ONCE is probably pointless.
> 
>> Then again, order-0 pages are considered cheap enough that they never
>> even fail in our current implementation.
>>
>> Which brings me to my other point: why not just a simple single-page
>> allocation?
> 
> No objection from me. I was previously thinking about the "proper"
> size for something that is a file name. So I originally wanted to use
> PATH_MAX instead but ended up with PAGE_SIZE for reasons I do not
> remember now.

theoretically, this is PATH_MAX + max cache name.


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