Date: Wed, 27 Mar 2013 16:47:00 +0100
From: Michal Hocko <mhocko@suse.cz>
To: Johannes Weiner <hannes@cmpxchg.org>
Cc: Tejun Heo <tj@kernel.org>, Glauber Costa <glommer@parallels.com>,
        Li Zefan <lizefan@huawei.com>,
        KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>, linux-mm@kvack.org,
        cgroups@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] memcg: fix memcg_cache_name() to use cgroup_name()
Message-ID: <20130327154700.GM16579@dhcp22.suse.cz>
References: <1364373399-17397-1-git-send-email-mhocko@suse.cz>
 <20130327145727.GD29052@cmpxchg.org>
 <20130327151104.GK16579@dhcp22.suse.cz>
 <20130327153226.GF29052@cmpxchg.org>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <20130327153226.GF29052@cmpxchg.org>
User-Agent: Mutt/1.5.21 (2010-09-15)
Sender: linux-kernel-owner@vger.kernel.org
Content-Length: 1942
Lines: 50

On Wed 27-03-13 11:32:26, Johannes Weiner wrote:
> On Wed, Mar 27, 2013 at 04:11:04PM +0100, 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.  Maybe we can use NAME_MAX instead. I just do not like to
> > use page allocator directly when allocatating something like strings
> > etc...
> 
> Don't grep for GFP_TEMPORARY then, we do it in a couple places :-)

This is what Li suggested in the beginning and right, I didn't like it.

> NAME_MAX is just for single dentry names, not path names, no?  Might
> be a little short.

Yes, Glauber confirmed that MAX_PATH is needed.

-- 
Michal Hocko
SUSE Labs
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/