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

Michal Hocko
2013-03-27T15:32:20Z

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.

--
Michal Hocko
SUSE Labs

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