linux-kernel - Re: [PATCH 5/5] mm, memcontrol: use vma_is

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Message-ID: <20150713130812.GA8115@cmpxchg.org>
Date:	Mon, 13 Jul 2015 09:08:12 -0400
From:	Johannes Weiner <hannes@...xchg.org>
To:	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Oleg Nesterov <oleg@...hat.com>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, Michal Hocko <mhocko@...e.cz>
Subject: Re: [PATCH 5/5] mm, memcontrol: use vma_is_anonymous() to check for
 anon VMA

On Mon, Jul 13, 2015 at 01:54:12PM +0300, Kirill A. Shutemov wrote:
> !vma->vm_file is not reliable to detect anon VMA, because not all
> drivers bother set it. Let's use vma_is_anonymous() instead.
> 
> Signed-off-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
> Cc: Johannes Weiner <hannes@...xchg.org>
> Cc: Michal Hocko <mhocko@...e.cz>
> ---
>  mm/memcontrol.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index acb93c554f6e..a624709f0dd7 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -4809,7 +4809,7 @@ static struct page *mc_handle_file_pte(struct vm_area_struct *vma,
>  	struct address_space *mapping;
>  	pgoff_t pgoff;
>  
> -	if (!vma->vm_file) /* anonymous vma */
> +	if (vma_is_anonymous(vma)) /* anonymous vma */
>  		return NULL;
>  	if (!(mc.flags & MOVE_FILE))
>  		return NULL;

The next line does vma->vm_file->f_mapping, so it had better be !NULL.

It's not about reliably detecting anonymous vs. file, it is about
whether there is a mapping against which we can do find_get_page().
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