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SubjectRe: [PATCH 02/23] memcg, thp: charge huge cache pages
On Sun 04-08-13 05:17:04, Kirill A. Shutemov wrote:
> From: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
>
> mem_cgroup_cache_charge() has check for PageCompound(). The check
> prevents charging huge cache pages.
>
> I don't see a reason why the check is present. Looks like it's just
> legacy (introduced in 52d4b9a memcg: allocate all page_cgroup at boot).
>
> Let's just drop it.

If the page cache charging path only sees THP as compound pages then OK.
Can we keep at least VM_BUG_ON(PageCompound(page) && !PageTransHuge(page))

Otherwise mem_cgroup_charge_common would be confused and charge such a
page as order-0

> Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
> Cc: Michal Hocko <mhocko@suse.cz>
> Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
> Acked-by: Dave Hansen <dave.hansen@linux.intel.com>

Other than that, looks good to me.
Acked-by: Michal Hocko <mhocko@suse.cz>

> ---
> mm/memcontrol.c | 2 --
> 1 file changed, 2 deletions(-)
>
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index b6cd870..dc50c1a 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -3921,8 +3921,6 @@ int mem_cgroup_cache_charge(struct page *page, struct mm_struct *mm,
>
> if (mem_cgroup_disabled())
> return 0;
> - if (PageCompound(page))
> - return 0;
>
> if (!PageSwapCache(page))
> ret = mem_cgroup_charge_common(page, mm, gfp_mask, type);
> --
> 1.8.3.2
>

--
Michal Hocko
SUSE Labs


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