linux-kernel - Re: [PATCH -V8 10/16] hugetlb/cgroup: Add the cgroup pointer to page lru

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Message-ID: <87oboq5ifb.fsf@skywalker.in.ibm.com>
Date:	Mon, 11 Jun 2012 14:33:52 +0530
From:	"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>
To:	Michal Hocko <mhocko@...e.cz>
Cc:	linux-mm@...ck.org, kamezawa.hiroyu@...fujitsu.com,
	dhillf@...il.com, rientjes@...gle.com, akpm@...ux-foundation.org,
	hannes@...xchg.org, linux-kernel@...r.kernel.org,
	cgroups@...r.kernel.org
Subject: Re: [PATCH -V8 10/16] hugetlb/cgroup: Add the cgroup pointer to page lru

Michal Hocko <mhocko@...e.cz> writes:

> On Sat 09-06-12 14:29:55, Aneesh Kumar K.V wrote:
>> From: "Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>
>> 
>> Add the hugetlb cgroup pointer to 3rd page lru.next.
>
> Interesting and I really like the idea much more than tracking by
> page_cgroup.
>
>> This limit the usage to hugetlb cgroup to only hugepages with 3 or
>> more normal pages. I guess that is an acceptable limitation.
>
> Agreed.
>
>> Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@...ux.vnet.ibm.com>
>
> Other than some nits I like this.
> Thanks!
>
>> ---
>>  include/linux/hugetlb_cgroup.h |   31 +++++++++++++++++++++++++++++++
>>  mm/hugetlb.c                   |    4 ++++
>>  2 files changed, 35 insertions(+)
>> 
>> diff --git a/include/linux/hugetlb_cgroup.h b/include/linux/hugetlb_cgroup.h
>> index 5794be4..ceff1d5 100644
>> --- a/include/linux/hugetlb_cgroup.h
>> +++ b/include/linux/hugetlb_cgroup.h
>> @@ -26,6 +26,26 @@ struct hugetlb_cgroup {
>>  };
>>  
>>  #ifdef CONFIG_CGROUP_HUGETLB_RES_CTLR
>> +static inline struct hugetlb_cgroup *hugetlb_cgroup_from_page(struct page *page)
>> +{
>> +	if (!PageHuge(page))
>> +		return NULL;
>> +	if (compound_order(page) < 3)
>
> Why 3? I think you wanted 2 here, right?

Yes that should be 2. I updated that in an earlier. Already in v9
version I have locally.

>
>> +		return NULL;
>> +	return (struct hugetlb_cgroup *)page[2].lru.next;
>> +}
>> +
>> +static inline
>> +int set_hugetlb_cgroup(struct page *page, struct hugetlb_cgroup *h_cg)
>> +{
>> +	if (!PageHuge(page))
>> +		return -1;
>> +	if (compound_order(page) < 3)
>
> Here as well.
>
>> +		return -1;
>> +	page[2].lru.next = (void *)h_cg;
>> +	return 0;
>> +}
>> +
>>  static inline bool hugetlb_cgroup_disabled(void)
>>  {
>>  	if (hugetlb_subsys.disabled)
>> @@ -43,6 +63,17 @@ 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);
>>  #else
>> +static inline struct hugetlb_cgroup *hugetlb_cgroup_from_page(struct page *page)
>> +{
>> +	return NULL;
>> +}
>> +
>> +static inline
>> +int set_hugetlb_cgroup(struct page *page, struct hugetlb_cgroup *h_cg)
>> +{
>> +	return 0;
>> +}
>> +
>>  static inline bool hugetlb_cgroup_disabled(void)
>>  {
>>  	return true;
>> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
>> index e899a2d..1ca2d8f 100644
>> --- a/mm/hugetlb.c
>> +++ b/mm/hugetlb.c
>> @@ -28,6 +28,7 @@
>>  
>>  #include <linux/io.h>
>>  #include <linux/hugetlb.h>
>> +#include <linux/hugetlb_cgroup.h>
>>  #include <linux/node.h>
>>  #include "internal.h"
>>  
>> @@ -591,6 +592,7 @@ static void update_and_free_page(struct hstate *h, struct page *page)
>>  				1 << PG_active | 1 << PG_reserved |
>>  				1 << PG_private | 1 << PG_writeback);
>>  	}
>> +	BUG_ON(hugetlb_cgroup_from_page(page));
>
> What about VM_BUG_ON?

Will do, So when do one decide to choose VM_BUG_ON against BUG_ON ?

>
>>  	set_compound_page_dtor(page, NULL);
>>  	set_page_refcounted(page);
>>  	arch_release_hugepage(page);
>> @@ -643,6 +645,7 @@ static void prep_new_huge_page(struct hstate *h, struct page *page, int nid)
>>  	INIT_LIST_HEAD(&page->lru);
>>  	set_compound_page_dtor(page, free_huge_page);
>>  	spin_lock(&hugetlb_lock);
>> +	set_hugetlb_cgroup(page, NULL);
>
> Why inside the spin lock?

All page[2].lru.next update is protected by hugetlb_lock . It should not
really matter here, because the pages are not yet available to use.

>
>>  	h->nr_huge_pages++;
>>  	h->nr_huge_pages_node[nid]++;
>>  	spin_unlock(&hugetlb_lock);
>> @@ -892,6 +895,7 @@ static struct page *alloc_buddy_huge_page(struct hstate *h, int nid)
>>  		INIT_LIST_HEAD(&page->lru);
>>  		r_nid = page_to_nid(page);
>>  		set_compound_page_dtor(page, free_huge_page);
>> +		set_hugetlb_cgroup(page, NULL);
>>  		/*
>>  		 * We incremented the global counters already
>>  		 */
>> -- 

-aneesh

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