linux-kernel - Re: [ofa-general] Re: [patch 0/6] MMU Notifiers V6

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Message-ID: <20080209015659.GC7051@v2.random>
Date:	Sat, 9 Feb 2008 02:56:59 +0100
From:	Andrea Arcangeli <andrea@...ranet.com>
To:	Christoph Lameter <clameter@....com>
Cc:	Roland Dreier <rdreier@...co.com>, a.p.zijlstra@...llo.nl,
	izike@...ranet.com, steiner@....com, linux-kernel@...r.kernel.org,
	avi@...ranet.com, linux-mm@...ck.org, daniel.blueman@...drics.com,
	Robin Holt <holt@....com>, general@...ts.openfabrics.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	kvm-devel@...ts.sourceforge.net, Rik van Riel <riel@...hat.com>
Subject: Re: [ofa-general] Re: [patch 0/6] MMU Notifiers V6

On Fri, Feb 08, 2008 at 05:27:03PM -0800, Christoph Lameter wrote:
> Pages will still be on the LRU and cycle through rmap again and again. 
> If page migration is used on those pages then the code may make repeated 
> attempt to migrate the page thinking that the page count must at some 
> point drop.
>
> I do not think that the page count was intended to be used to pin pages 
> permanently. If we had a marker on such pages then we could take them off 
> the LRU and not try to migrate them.

The VM shouldn't break if try_to_unmap doesn't actually make the page
freeable for whatever reason. Permanent pins shouldn't happen anyway,
so defining an ad-hoc API for that doesn't sound too appealing. Not
sure if old hardware deserves those special lru-size-reduction
optimizations but it's not my call (certainly swapoff/mlock would get
higher priority in that lru-size-reduction area).
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