linux-kernel - Re: [PATCH v4 2/7] deactivate invalidated pages

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Date:	Wed, 8 Dec 2010 11:15:19 +0900
From:	Minchan Kim <minchan.kim@...il.com>
To:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Cc:	Johannes Weiner <hannes@...xchg.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Rik van Riel <riel@...hat.com>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	linux-mm <linux-mm@...ck.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Wu Fengguang <fengguang.wu@...el.com>,
	Nick Piggin <npiggin@...nel.dk>, Mel Gorman <mel@....ul.ie>,
	Balbir Singh <balbir@...ux.vnet.ibm.com>
Subject: Re: [PATCH v4 2/7] deactivate invalidated pages

On Wed, Dec 8, 2010 at 10:56 AM, KAMEZAWA Hiroyuki
<kamezawa.hiroyu@...fujitsu.com> wrote:
> On Wed, 8 Dec 2010 10:43:08 +0900
> Minchan Kim <minchan.kim@...il.com> wrote:
>
>> Hi Kame,
>>
> Hi,
>
>> > I wonder ...how about adding "victim" list for "Reclaim" pages ? Then, we don't need
>> > extra LRU rotation.
>>
>> It can make the code clean.
>> As far as I think, victim list does following as.
>>
>> 1. select victim pages by strong hint
>> 2. move the page from LRU to victim
>> 3. reclaimer always peeks victim list before diving into LRU list.
>> 4-1. If the victim pages is used by others or dirty, it can be moved
>> into LRU, again or remain the page in victim list.
>> If the page is remained victim, when do we move it into LRU again if
>> the reclaimer continues to fail the page?
> When sometone touches it.
>
>> We have to put the new rule.
>> 4-2. If the victim pages isn't used by others and clean, we can
>> reclaim the page asap.
>>
>> AFAIK, strong hints are just two(invalidation, readahead max window heuristic).
>> I am not sure it's valuable to add new hierarchy(ie, LRU, victim,
>> unevictable) for cleaning the minor codes.
>> In addition, we have to put the new rule so it would make the LRU code
>> complicated.
>> I remember how unevictable feature merge is hard.
>>
> yes, it was hard.
>
>> But I am not against if we have more usecases. In this case, it's
>> valuable to implement it although it's not easy.
>>
>
> I wonder "victim list" can be used for something like Cleancache, when
> we have very-low-latency backend devices.
> And we may able to have page-cache-limit, which Balbir proposed as.

Yes, I thought that, too. I think it would be a good feature in embedded system.

>
>  - kvictimed? will move unmappedd page caches to victim list
> This may work like a InactiveClean list which we had before and make
> sizing easy.
>

Before further discuss, we need customer's confirm.
We know very well it is very hard to merge if anyone doesn't use.

Balbir, What do think about it?


> Thanks,
> -Kame
>
>
>
>



-- 
Kind regards,
Minchan Kim
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