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Date:	Tue, 01 Dec 2009 23:57:21 -0500
From:	Rik van Riel <riel@...hat.com>
To:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
CC:	Larry Woodman <lwoodman@...hat.com>, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org, akpm@...ux-foundation.org,
	Hugh Dickins <hugh.dickins@...cali.co.uk>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Andrea Arcangeli <aarcange@...hat.com>
Subject: Re: [PATCH] Replace page_mapping_inuse() with page_mapped()

On 12/01/2009 10:28 PM, KOSAKI Motohiro wrote:
>> On 12/01/2009 09:55 PM, KOSAKI Motohiro wrote:
>>      
>>>> btw, current shrink_active_list() have unnecessary page_mapping_inuse() call.
>>>> it prevent to drop page reference bit from unmapped cache page. it mean
>>>> we protect unmapped cache page than mapped page. it is strange.
>>>>
>>>>          
>>> How about this?
>>>
>>> ---------------------------------
>>> SplitLRU VM replacement algorithm assume shrink_active_list() clear
>>> the page's reference bit. but unnecessary page_mapping_inuse() test
>>> prevent it.
>>>
>>> This patch remove it.
>>>
>>>        
>> Shrink_page_list ignores the referenced bit on pages
>> that are !page_mapping_inuse().
>>
>>                   if (sc->order<= PAGE_ALLOC_COSTLY_ORDER&&
>>                                           referenced&&
>> page_mapping_inuse(page)
>> &&  !(vm_flags&  VM_LOCKED))
>>                           goto activate_locked;
>>
>> The reason we leave the referenced bit on unmapped
>> pages is that we want the next reference to a deactivated
>> page cache page to move that page back to the active
>> list.  We do not want to require that such a page gets
>> accessed twice before being reactivated while on the
>> inactive list, because (1) we know it was a frequently
>> accessed page already and (2) ongoing streaming IO
>> might evict it from the inactive list before it gets accessed
>> twice.
>>
>> Arguably, we should just replace the page_mapping_inuse()
>> in both places with page_mapped() to simplify things.
>>      
> Ah, yes. /me was slept. thanks correct me.
>
>
>  From 61340720e6e66b645db8d5410e89fd3b67eda907 Mon Sep 17 00:00:00 2001
> From: KOSAKI Motohiro<kosaki.motohiro@...fujitsu.com>
> Date: Wed, 2 Dec 2009 12:05:26 +0900
> Subject: [PATCH] Replace page_mapping_inuse() with page_mapped()
>
> page reclaim logic need to distingish mapped and unmapped pages.
> However page_mapping_inuse() don't provide proper test way. it test
> the address space (i.e. file) is mmpad(). Why `page' reclaim need
> care unrelated page's mapped state? it's unrelated.
>
> Thus, This patch replace page_mapping_inuse() with page_mapped()
>
> Signed-off-by: KOSAKI Motohiro<kosaki.motohiro@...fujitsu.com>
>    
Reviewed-by: Rik van Riel <riel@...hat.com>
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