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

Michal Hocko
2013-03-27T15:11:04Z

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...

To be honest, I do not care much which way to go.

> This just seems a little overelaborate. I think this path would be
> taken predominantly after cgroup creation and fork where we do a bunch
> of allocations anyway. And it happens asynchroneously from userspace,
> so it's not even really performance critical.

--
Michal Hocko
SUSE Labs