Re: [PATCH] mm/hugetlb: create hugetlb cgroup file in hugetlb_init

[Simon Jeons <simon.jeons-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>]

On Wed, 2012-12-12 at 12:23 +0100, Michal Hocko wrote:
> On Wed 12-12-12 18:44:13, Xishi Qiu wrote:
> > On 2012/12/12 18:19, Michal Hocko wrote:
> > 
> > > On Wed 12-12-12 16:25:59, Jianguo Wu wrote:
> > >> Build kernel with CONFIG_HUGETLBFS=y,CONFIG_HUGETLB_PAGE=y
> > >> and CONFIG_CGROUP_HUGETLB=y, then specify hugepagesz=xx boot option,
> > >> system will boot fail.
> > >>
> > >> This failure is caused by following code path:
> > >> setup_hugepagesz
> > >> 	hugetlb_add_hstate
> > >> 		hugetlb_cgroup_file_init
> > >> 			cgroup_add_cftypes
> > >> 				kzalloc <--slab is *not available* yet
> > >>
> > >> For this path, slab is not available yet, so memory allocated will be
> > >> failed, and cause WARN_ON() in hugetlb_cgroup_file_init().
> > >>
> > >> So I move hugetlb_cgroup_file_init() into hugetlb_init().
> > > 
> > > I do not think this is a good idea. hugetlb_init is in __init section as
> > > well so what guarantees that the slab is initialized by then? Isn't this
> > > just a good ordering that makes this working?
> > 
> > Hi Michal,
> > 
> > __initcall functions will be called in
> > start_kernel()
> > 	rest_init()  // -> slab is already
> > 		kernel_init()
> > 			kernel_init_freeable()
> > 				do_basic_setup()
> > 					do_initcalls()
> > 
> > and setup_hugepagesz() will be called in
> > start_kernel()
> > 	parse_early_param()  // -> before mm_init() -> kmem_cache_init()
> > 
> > Is this right?
> 
> Yes this is right. I just noticed that kmem_cache_init_late is an __init
> function as well and didn't realize it is called directly. Sorry about
> the confusion.
> Anyway I still think it would be a better idea to move the call into the
> hugetlb_cgroup_create callback where it is more logical IMO but now that
> I'm looking at other controllers (blk and kmem.tcp) they all do this from
> init calls as well. So it doesn't make sense to have hugetlb behave
> differently.

Which callback in cgroup_subsys should hugetlb_cgroup_create associated?
Currently, there is no such callback.  

> 
> So
> Acked-by: Michal Hocko <mhocko-AlSwsSmVLrQ@public.gmane.org>
> 
> Thanks!