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

[Konrad Rzeszutek Wilk <konrad@xxxxxxxxxx>]

On Sat, Jun 09, 2012 at 02:29:55PM +0530, Aneesh Kumar K.V wrote:
> From: "Aneesh Kumar K.V" <aneesh.kumar@xxxxxxxxxxxxxxxxxx>
> 
> Add the hugetlb cgroup pointer to 3rd page lru.next. This limit
> the usage to hugetlb cgroup to only hugepages with 3 or more
> normal pages. I guess that is an acceptable limitation.

Can you explain in a bit more detail the reasoning behind this
please? Either in the code in the hugetlb_cgroup_from_page
or in the git commit (or better - in both).

> 
> Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@xxxxxxxxxxxxxxxxxx>
> ---
>  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)
> +		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)
> +		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));
>  	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);
>  	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
>  		 */
> -- 
> 1.7.10
> 
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