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Date: Tue, 13 Jun 2006 22:24:37 +1000
From: Nick Piggin <nickpiggin@yahoo.com.au>
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To: Peter Zijlstra <a.p.zijlstra@chello.nl>
CC: Andi Kleen <ak@suse.de>, Hugh Dickins <hugh@veritas.com>,
       Andrew Morton <akpm@osdl.org>, David Howells <dhowells@redhat.com>,
       Christoph Lameter <christoph@lameter.com>,
       Martin Bligh <mbligh@google.com>, Nick Piggin <npiggin@suse.de>,
       Linus Torvalds <torvalds@osdl.org>, linux-kernel@vger.kernel.org
Subject: Re: [PATCH 1/6] mm: tracking shared dirty pages
References: <20060613112120.27913.71986.sendpatchset@lappy>	 <20060613112131.27913.43169.sendpatchset@lappy>	 <p73zmghqn2z.fsf@verdi.suse.de> <1150200914.20886.135.camel@lappy>
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Peter Zijlstra wrote:
> On Tue, 2006-06-13 at 14:03 +0200, Andi Kleen wrote:
> 
>>Peter Zijlstra <a.p.zijlstra@chello.nl> writes:
>>
>>
>>>From: Peter Zijlstra <a.p.zijlstra@chello.nl>
>>>
>>>People expressed the need to track dirty pages in shared mappings.
>>
>>Why only shared mappings? Anonymous pages can be dirty too
>>and would need to be written to swap then before making progress.
> 
> 
> Anonymous pages are per definition dirty, as they don't have a
> persistent backing store.

They can be clean.

> Each eviction of an anonymous page requires IO
> to swap space. On swap-in pages are removed from the swap space to make
> place for other pages.

No they can remain in swap too.

Swap is a bit different because the memory usage patters are going
to be much different. There is no reason why something similar couldn't
be done for swap as well, however I don't think there is so much need
for it that has been demonstrated.

-- 
SUSE Labs, Novell Inc.
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