linux-kernel - Re: [v4][PATCH 2/6] mm: swap: make 'struct page' and swp_entry_t variants of swapcache

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Message-ID: <20130603061320.GA2795@blaptop>
Date:	Mon, 3 Jun 2013 15:13:20 +0900
From:	Minchan Kim <minchan@...nel.org>
To:	Dave Hansen <dave@...1.net>
Cc:	linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	akpm@...ux-foundation.org, mgorman@...e.de,
	tim.c.chen@...ux.intel.com
Subject: Re: [v4][PATCH 2/6] mm: swap: make 'struct page' and swp_entry_t
 variants of swapcache_free().

Hello Dave,

On Fri, May 31, 2013 at 11:38:58AM -0700, Dave Hansen wrote:
> 
> From: Dave Hansen <dave.hansen@...ux.intel.com>
> 
> swapcache_free() takes two arguments:
> 
> 	void swapcache_free(swp_entry_t entry, struct page *page)
> 
> Most of its callers (5/7) are from error handling paths haven't even
> instantiated a page, so they pass page=NULL.  Both of the callers
> that call in with a 'struct page' create and pass in a temporary
> swp_entry_t.
> 
> Now that we are deferring clearing page_private() until after
> swapcache_free() has been called, we can just create a variant
> that takes a 'struct page' and does the temporary variable in
> the helper.
> 
> That leaves all the other callers doing
> 
> 	swapcache_free(entry, NULL)
> 
> so create another helper for them that makes it clear that they
> need only pass in a swp_entry_t.
> 
> One downside here is that delete_from_swap_cache() now does
> an extra swap_address_space() call.  But, those are pretty
> cheap (just some array index arithmetic).

I lost from this description.

Old behavior

delete_from_swap_cache
        swap_address_space
        __delete_from_swap_cache
                swap_address_space


New behavior

delete_from_swap_cache
        __delete_from_swap_cache
                swap_address_space
                
So you removes a swap_address_space, not adding a extra call.
Am I missing something?

> 
> Signed-off-by: Dave Hansen <dave.hansen@...ux.intel.com>

Otherwise, looks good to me
Reviewed-by: Minchan Kim <minchan@...nel.org>

-- 
Kind regards,
Minchan Kim
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