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

[Jianguo Wu]

On 2012/12/12 19:23, 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

Hi Michal,

Thanks for your review and comments:).
hugetlb_cgroup_create is a callback of hugetlb_subsys,
and hugetlb_cgroup_file_init add h->cgroup_files to hugetlb_subsys,
so we cann't move hugetlb_cgroup_file_init into hugetlb_cgroup_create, right?

Thanks,
Jianguo wu

> 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.
> 
> So
> Acked-by: Michal Hocko <mhocko@xxxxxxx>
> 
> Thanks!



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