linux-kernel - Re: [RFC][PATCH 1/7] defer clearing of page

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Message-ID: <20130514145537.GS11497@suse.de>
Date:	Tue, 14 May 2013 15:55:37 +0100
From:	Mel Gorman <mgorman@...e.de>
To:	Dave Hansen <dave@...1.net>
Cc:	linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	akpm@...ux-foundation.org, tim.c.chen@...ux.intel.com
Subject: Re: [RFC][PATCH 1/7] defer clearing of page_private() for swap cache
 pages

On Tue, May 07, 2013 at 02:19:55PM -0700, Dave Hansen wrote:
> 
> From: Dave Hansen <dave.hansen@...ux.intel.com>
> 
> There are only two callers of swapcache_free() which actually
> pass in a non-NULL 'struct page'.  Both of them
> (__remove_mapping and delete_from_swap_cache())  create a
> temporary on-stack 'swp_entry_t' and set entry.val to
> page_private().
> 
> They need to do this since __delete_from_swap_cache() does
> set_page_private(page, 0) and destroys the information.
> 
> However, I'd like to batch a few of these operations on several
> pages together in a new version of __remove_mapping(), and I
> would prefer not to have to allocate temporary storage for
> each page.  The code is pretty ugly, and it's a bit silly
> to create these on-stack 'swp_entry_t's when it is so easy to
> just keep the information around in 'struct page'.
> 
> There should not be any danger in doing this since we are
> absolutely on the path of freeing these page.  There is no
> turning back, and no other rerferences can be obtained
> after it comes out of the radix tree.
> 
> Signed-off-by: Dave Hansen <dave.hansen@...ux.intel.com>

On it's own, this patch looks like it has a lot missing but when
combined with patch 2, it starts making sense so

Acked-by: Mel Gorman <mgorman@...e.de>

-- 
Mel Gorman
SUSE Labs
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