Re: [PATCH] memcg: fix memcg_cache_name() to use cgroup_name()

[Michal Hocko]

On Wed 27-03-13 16:32:20, Michal Hocko wrote:
> On Wed 27-03-13 19:19:58, Glauber Costa wrote:
> > 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.
> 
> So do you prefer kmalloc(PATH_MAX) or the page allocator directly as
> Johannes suggests? I agree tha kamlloc(PAGE_SIZE) looks weird.

Removed WARN_ON_ONCE as suggested by Johannes and kept kmalloc with
PATH_MAX used instead of PAGE_SIZE. I've kept Glauber's acked-by but I
can remove it.
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