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

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Date:	Mon, 5 Nov 2012 18:03:48 -0800
From:	Arun Sharma <asharma@...com>
To:	Minchan Kim <minchan@...nel.org>
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

On 11/5/12 5:49 PM, Minchan Kim wrote:

>> 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? :)

By using a new anonymous map and faulting pages in.

The fragmented virtual memory is released via MADV_DONTNEED and if the 
malloc/free activity on the system is dominated by one process, chances 
are that the newly faulted in page is the one released by the same 
process :)

The net effect is that physical pages within a single address space are 
rearranged so larger allocations can be satisfied.

  -Arun
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