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Date: Sun, 4 Aug 2013 10:25:09 +0200
From: Michal Hocko <mhocko@suse.cz>
To: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Al Viro <viro@zeniv.linux.org.uk>, Hugh Dickins <hughd@google.com>,
        Wu Fengguang <fengguang.wu@intel.com>, Jan Kara <jack@suse.cz>,
        Mel Gorman <mgorman@suse.de>, linux-mm@kvack.org,
        Andi Kleen <ak@linux.intel.com>,
        Matthew Wilcox <willy@linux.intel.com>,
        "Kirill A. Shutemov" <kirill@shutemov.name>,
        Hillf Danton <dhillf@gmail.com>, Dave Hansen <dave@sr71.net>,
        Ning Qu <quning@google.com>, linux-fsdevel@vger.kernel.org,
        linux-kernel@vger.kernel.org,
        KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Subject: Re: [PATCH 02/23] memcg, thp: charge huge cache pages
Message-ID: <20130804082509.GC24005@dhcp22.suse.cz>
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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