Re: [PATCH] mm/hugetlb_cgroup: Add list_del to remove unused page from hugepage_activelist when hugepage migration

[Wanpeng Li <liwp.linux-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>]

On Wed, Jul 11, 2012 at 03:15:19PM +0530, Aneesh Kumar K.V wrote:
>Wanpeng Li <liwp.linux-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> writes:
>
>> On Wed, Jul 11, 2012 at 02:02:23PM +0530, Aneesh Kumar K.V wrote:
>>>Wanpeng Li <liwp.linux-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> writes:
>>>
>>>> From: Wanpeng Li <liwp-23VcF4HTsmIX0ybBhKVfKdBPR1lH4CV8@public.gmane.org>
>>>>
>>>> hugepage_activelist is used to track currently used HugeTLB pages.
>>>> We can find the in-use HugeTLB pages to support HugeTLB cgroup
>>>> removal. Don't keep unused page in hugetlb_activelist too long.
>>>> Otherwise, on cgroup removal we should update the unused page's 
>>>> charge to parent count. To reduce this overhead, remove unused page 
>>>> from hugepage_activelist immediately.
>>>>
>>>> Signed-off-by: Wanpeng Li <liwp.linux-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
>>>> ---
>>>>  mm/hugetlb_cgroup.c |    1 +
>>>>  1 files changed, 1 insertions(+), 0 deletions(-)
>>>>
>>>> diff --git a/mm/hugetlb_cgroup.c b/mm/hugetlb_cgroup.c
>>>> index b834e8d..d819d66 100644
>>>> --- a/mm/hugetlb_cgroup.c
>>>> +++ b/mm/hugetlb_cgroup.c
>>>> @@ -398,6 +398,7 @@ void hugetlb_cgroup_migrate(struct page *oldhpage, struct page *newhpage)
>>>>  	spin_lock(&hugetlb_lock);
>>>>  	h_cg = hugetlb_cgroup_from_page(oldhpage);
>>>>  	set_hugetlb_cgroup(oldhpage, NULL);
>>>> +	list_del(&oldhpage->lru);
>>>>
>>>>  	/* move the h_cg details to new cgroup */
>>>>  	set_hugetlb_cgroup(newhpage, h_cg);
>>>
>>>put_page on the oldhpage will do that. If we do list_del here
>>>free_huge_page() will have error list_move().
>>
>> I don't know if move the page to other lists when migration in order 
>> to reduce overhead I mentioned make sense. :-)
>>
>
>Even if we are in the active_list, we don't get anything wrong because
>hugetlb cgroup is set to NULL for the old hugetlb page. The above patch is
>wrong and will result in crash when we try to put_page the oldhpage.

Hi aneesh, I am happy we are in the same company. I am a guy in LTC
China. I want to know if there any features or works about hugetlb
cgroup I can do with you!

Regards,
Wanpeng Li

>
>-aneesh
>
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