linux-kernel - Re: [PATCH 5/9] mm/rmap: extend rmap_walk

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Date:	Mon, 02 Dec 2013 15:09:42 -0500
From:	Naoya Horiguchi <n-horiguchi@...jp.nec.com>
To:	Joonsoo Kim <iamjoonsoo.kim@....com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Mel Gorman <mgorman@...e.de>, Hugh Dickins <hughd@...gle.com>,
	Rik van Riel <riel@...hat.com>,
	Ingo Molnar <mingo@...nel.org>,
	Hillf Danton <dhillf@...il.com>, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org, Joonsoo Kim <js1304@...il.com>
Subject: Re: [PATCH 5/9] mm/rmap: extend rmap_walk_xxx() to cope with
 different cases

On Thu, Nov 28, 2013 at 04:48:42PM +0900, Joonsoo Kim wrote:
> There are a lot of common parts in traversing functions, but there are
> also a little of uncommon parts in it. By assigning proper function
> pointer on each rmap_walker_control, we can handle these difference
> correctly.
> 
> Following are differences we should handle.
> 
> 1. difference of lock function in anon mapping case
> 2. nonlinear handling in file mapping case
> 3. prechecked condition:
> 	checking memcg in page_referenced(),
> 	checking VM_SHARE in page_mkclean()
> 	checking temporary vma in try_to_unmap()
> 4. exit condition:
> 	checking page_mapped() in try_to_unmap()
> 
> So, in this patch, I introduce 4 function pointers to
> handle above differences.
> 
> Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@....com>
> 
> diff --git a/include/linux/rmap.h b/include/linux/rmap.h
> index 0f65686..58624b4 100644
> --- a/include/linux/rmap.h
> +++ b/include/linux/rmap.h
> @@ -239,6 +239,12 @@ struct rmap_walk_control {
>  	int (*main)(struct page *, struct vm_area_struct *,
>  					unsigned long, void *);
>  	void *arg;	/* argument to main function */
> +	int (*main_done)(struct page *page);	/* check exit condition */
> +	int (*file_nonlinear)(struct page *, struct address_space *,
> +					struct vm_area_struct *vma);
> +	struct anon_vma *(*anon_lock)(struct page *);
> +	int (*vma_skip)(struct vm_area_struct *, void *);

Can you add some comments about how these callbacks work and when it
should be set to for future users?  For example, anon_lock() are
used to override the default behavior and it's not trivial.

> +	void *skip_arg;	/* argument to vma_skip function */

I think that it's better to move this field into the structure pointed
to by arg (which can be defined by each caller in its own way) and pass
arg to *vma_skip().

Thanks,
Naoya Horiguchi
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