linux-kernel - Re: [RFC v2] Support volatile range for anon vma

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Date:	Tue, 6 Nov 2012 10:49:32 +0900
From:	Minchan Kim <minchan@...nel.org>
To:	Arun Sharma <asharma@...com>
Cc:	KOSAKI Motohiro <kosaki.motohiro@...il.com>,
	Paul Turner <pjt@...gle.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	John Stultz <john.stultz@...aro.org>,
	Christoph Lameter <cl@...ux.com>,
	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>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	sanjay@...gle.com, David Rientjes <rientjes@...gle.com>
Subject: Re: [RFC v2] Support volatile range for anon vma

Hello,

On Mon, Nov 05, 2012 at 03:54:43PM -0800, Arun Sharma wrote:
> On Wed, Oct 31, 2012 at 06:56:05PM -0400, KOSAKI Motohiro wrote:
> > glibc malloc discard freed memory by using MADV_DONTNEED
> > as tcmalloc. and it is often a source of large performance decrease.
> > because of MADV_DONTNEED discard memory immediately and
> > right after malloc() call fall into page fault and pagesize memset() path.
> > then, using DONTNEED increased zero fill and cache miss rate.
> 
> The memcg based solution that I posted a few months ago is working well
> for us. We see significantly less cpu in zero'ing pages.
> 
> Not everyone was comfortable with the security implications of recycling
> pages between processes in a memcg, although it was disabled by default
> and had to be explicitly opted-in.
> 
> Also, memory allocators have a second motivation in using madvise: to
> create virtually contiguous regions of memory from a fragmented address 
> space, without increasing the RSS.

I don't get it. How do we create contiguos region by madvise?
Just out of curiosity.
Could you elaborate that use case? :)

> 
>  -Arun
> 
> --
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-- 
Kind Regards,
Minchan Kim
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