linux-kernel - Re: [PATCH -V8 15/16] hugetlb/cgroup: migrate hugetlb cgroup info from oldpage to new page during migration

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Date:	Tue, 12 Jun 2012 16:30:16 +0530
From:	"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>
To:	Kamezawa Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Cc:	linux-mm@...ck.org, dhillf@...il.com, rientjes@...gle.com,
	mhocko@...e.cz, akpm@...ux-foundation.org, hannes@...xchg.org,
	linux-kernel@...r.kernel.org, cgroups@...r.kernel.org
Subject: Re: [PATCH -V8 15/16] hugetlb/cgroup: migrate hugetlb cgroup info from oldpage to new page during migration

Kamezawa Hiroyuki <kamezawa.hiroyu@...fujitsu.com> writes:

> (2012/06/09 18:00), Aneesh Kumar K.V wrote:
>> From: "Aneesh Kumar K.V"<aneesh.kumar@...ux.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@...ux.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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