linux-kernel - Re: [PATCH v3 1/3] mm: don't call __page_cache

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Message-ID: <20150401161358.GA12808@dhcp22.suse.cz>
Date:	Wed, 1 Apr 2015 18:13:58 +0200
From:	Michal Hocko <mhocko@...e.cz>
To:	Naoya Horiguchi <n-horiguchi@...jp.nec.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Hugh Dickins <hughd@...gle.com>, Mel Gorman <mgorman@...e.de>,
	Johannes Weiner <hannes@...xchg.org>,
	David Rientjes <rientjes@...gle.com>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Naoya Horiguchi <nao.horiguchi@...il.com>
Subject: Re: [PATCH v3 1/3] mm: don't call __page_cache_release for hugetlb

On Tue 31-03-15 08:50:45, Naoya Horiguchi wrote:
> __put_compound_page() calls __page_cache_release() to do some freeing works,
> but it's obviously for thps, not for hugetlb. We didn't care it because PageLRU
> is always cleared and page->mem_cgroup is always NULL for hugetlb.
> But it's not correct and has potential risks, so let's make it conditional.
> 
> Signed-off-by: Naoya Horiguchi <n-horiguchi@...jp.nec.com>

Reviewed-by: Michal Hocko <mhocko@...e.cz>

> ---
>  mm/swap.c | 10 +++++++++-
>  1 file changed, 9 insertions(+), 1 deletion(-)
> 
> diff --git v4.0-rc6.orig/mm/swap.c v4.0-rc6/mm/swap.c
> index cd3a5e64cea9..8e46823c3319 100644
> --- v4.0-rc6.orig/mm/swap.c
> +++ v4.0-rc6/mm/swap.c
> @@ -31,6 +31,7 @@
>  #include <linux/memcontrol.h>
>  #include <linux/gfp.h>
>  #include <linux/uio.h>
> +#include <linux/hugetlb.h>
>  
>  #include "internal.h"
>  
> @@ -75,7 +76,14 @@ static void __put_compound_page(struct page *page)
>  {
>  	compound_page_dtor *dtor;
>  
> -	__page_cache_release(page);
> +	/*
> +	 * __page_cache_release() is supposed to be called for thp, not for
> +	 * hugetlb. This is because hugetlb page does never have PageLRU set
> +	 * (it's never listed to any LRU lists) and no memcg routines should
> +	 * be called for hugetlb (it has a separate hugetlb_cgroup.)
> +	 */
> +	if (!PageHuge(page))
> +		__page_cache_release(page);
>  	dtor = get_compound_page_dtor(page);
>  	(*dtor)(page);
>  }
> -- 
> 1.9.3

-- 
Michal Hocko
SUSE Labs
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