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

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Message-ID: <20101208065650.GP3158@balbir.in.ibm.com>
Date:	Wed, 8 Dec 2010 12:26:50 +0530
From:	Balbir Singh <balbir@...ux.vnet.ibm.com>
To:	Minchan Kim <minchan.kim@...il.com>
Cc:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	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

* MinChan Kim <minchan.kim@...il.com> [2010-12-08 11:15:19]:

> 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?
> 

The idea seems interesting, I am in the process of refreshing my
patches for unmapped page cache control. I presume the process of
filling the victim list will be similar to what I have or unmapped
page cache isolation.

> 
> > Thanks,
> > -Kame
> >
> >
> >
> >
> 
> 
> 
> -- 
> Kind regards,
> Minchan Kim

-- 
	Three Cheers,
	Balbir
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