linux-kernel - Re: [RFC] Support volatile range for anon vma

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Message-ID: <20121102023220.GA3326@bbox>
Date:	Fri, 2 Nov 2012 11:32:20 +0900
From:	Minchan Kim <minchan@...nel.org>
To:	Christoph Lameter <cl@...ux.com>
Cc:	linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	John Stultz <john.stultz@...aro.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Android Kernel Team <kernel-team@...roid.com>,
	Robert Love <rlove@...gle.com>, Mel Gorman <mel@....ul.ie>,
	Hugh Dickins <hughd@...gle.com>,
	Dave Hansen <dave@...ux.vnet.ibm.com>,
	Rik van Riel <riel@...hat.com>,
	Dave Chinner <david@...morbit.com>, Neil Brown <neilb@...e.de>,
	Mike Hommey <mh@...ndium.org>, Taras Glek <tglek@...illa.com>,
	KOSAKI Motohiro <kosaki.motohiro@...il.com>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Subject: Re: [RFC] Support volatile range for anon vma

Hi Christoph,

On Thu, Nov 01, 2012 at 08:26:09PM +0000, Christoph Lameter wrote:
> On Fri, 26 Oct 2012, Minchan Kim wrote:
> 
> > I guess it would improve system performance very well.
> > But as I wrote down in description, downside of the patch is that we have to
> > age anon lru although we don't have swap. But gain via the patch is bigger than
> > loss via aging of anon lru when memory pressure happens. I don't see other downside
> > other than it. What do you think about it?
> > (I didn't implement anon lru aging in case of no-swap but it's trivial
> > once we decide)
> 
> 
> I am a bit confused like some of the others as to why this patch is
> necessary since we already have DONT_NEED.

Totally, my fault. I should have written clearly.

DONT_NEED have to zap all pte entries/tlb flush when system call
happens so DONT_NEED isn't cheap.
Even, later if user accesses address again, page fault happens.

This patch is to remove above two overheads.
while I discussed with KOSAKI, I found there was trial of simillar
goal by Rik. https://lkml.org/lkml/2007/4/17/53
But as I look over the code, it seems to have a cost about setting PG_lazyfree
on all pages of range which isn't in my implementation.

Anyway, I would like to know where Rik's patch wasn't merged at that time.

> 
> --
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-- 
Kind regards,
Minchan Kim
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