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SubjectRe: [PATCH -V8 15/16] hugetlb/cgroup: migrate hugetlb cgroup info from oldpage to new page during migration
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Kamezawa Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> writes:

> (2012/06/09 18:00), Aneesh Kumar K.V wrote:
>> From: "Aneesh Kumar K.V"<aneesh.kumar@linux.vnet.ibm.com>
>>
>> With HugeTLB pages, hugetlb cgroup is uncharged in compound page destructor. Since
>> we are holding a hugepage reference, we can be sure that old page won't
>> get uncharged till the last put_page().
>>
>> Signed-off-by: Aneesh Kumar K.V<aneesh.kumar@linux.vnet.ibm.com>
>
> one comment.
>
>> ---
>> include/linux/hugetlb_cgroup.h | 8 ++++++++
>> mm/hugetlb_cgroup.c | 21 +++++++++++++++++++++
>> mm/migrate.c | 5 +++++
>> 3 files changed, 34 insertions(+)
>>
>> diff --git a/include/linux/hugetlb_cgroup.h b/include/linux/hugetlb_cgroup.h
>> index ba4836f..b64d067 100644
>> --- a/include/linux/hugetlb_cgroup.h
>> +++ b/include/linux/hugetlb_cgroup.h
>> @@ -63,6 +63,8 @@ extern void hugetlb_cgroup_uncharge_page(int idx, unsigned long nr_pages,
>> extern void hugetlb_cgroup_uncharge_cgroup(int idx, unsigned long nr_pages,
>> struct hugetlb_cgroup *h_cg);
>> extern int hugetlb_cgroup_file_init(int idx) __init;
>> +extern void hugetlb_cgroup_migrate(struct page *oldhpage,
>> + struct page *newhpage);
>> #else
>> static inline struct hugetlb_cgroup *hugetlb_cgroup_from_page(struct page *page)
>> {
>> @@ -112,5 +114,11 @@ static inline int __init hugetlb_cgroup_file_init(int idx)
>> {
>> return 0;
>> }
>> +
>> +static inline void hugetlb_cgroup_migrate(struct page *oldhpage,
>> + struct page *newhpage)
>> +{
>> + return;
>> +}
>> #endif /* CONFIG_MEM_RES_CTLR_HUGETLB */
>> #endif
>> diff --git a/mm/hugetlb_cgroup.c b/mm/hugetlb_cgroup.c
>> index c2b7b8e..2d384fe 100644
>> --- a/mm/hugetlb_cgroup.c
>> +++ b/mm/hugetlb_cgroup.c
>> @@ -394,6 +394,27 @@ int __init hugetlb_cgroup_file_init(int idx)
>> return 0;
>> }
>>
>> +void hugetlb_cgroup_migrate(struct page *oldhpage, struct page *newhpage)
>> +{
>> + struct hugetlb_cgroup *h_cg;
>> +
>> + VM_BUG_ON(!PageHuge(oldhpage));
>> +
>> + if (hugetlb_cgroup_disabled())
>> + return;
>> +
>> + spin_lock(&hugetlb_lock);
>> + h_cg = hugetlb_cgroup_from_page(oldhpage);
>> + set_hugetlb_cgroup(oldhpage, NULL);
>> + cgroup_exclude_rmdir(&h_cg->css);
>> +
>> + /* move the h_cg details to new cgroup */
>> + set_hugetlb_cgroup(newhpage, h_cg);
>> + spin_unlock(&hugetlb_lock);
>> + cgroup_release_and_wakeup_rmdir(&h_cg->css);
>> + return;
>
>
> Why do you need cgroup_exclude/release rmdir here ? you holds hugetlb_lock()
> and charges will not be empty, here.
>

But even without empty charge, we can still remove the cgroup right ?
ie if we don't have any task but some charge in the cgroup because of
shared mmap in hugetlbfs.

-aneesh



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