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

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Date:	Wed, 8 Dec 2010 10:56:37 +0900
From:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To:	Minchan Kim <minchan.kim@...il.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>
Subject: Re: [PATCH v4 2/7] deactivate invalidated pages

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.

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

Thanks,
-Kame



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