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[Xen-devel] Re: [RFC PATCH 0/4] (Take 2): transcendent memory ("tmem") f

To: Dan Magenheimer <dan.magenheimer@xxxxxxxxxx>
Subject: [Xen-devel] Re: [RFC PATCH 0/4] (Take 2): transcendent memory ("tmem") for Linux
From: Rik van Riel <riel@xxxxxxxxxx>
Date: Thu, 09 Jul 2009 17:27:39 -0400
Cc: npiggin@xxxxxxx, akpm@xxxxxxxx, jeremy@xxxxxxxx, xen-devel@xxxxxxxxxxxxxxxxxxx, tmem-devel@xxxxxxxxxxxxxx, kurt.hackel@xxxxxxxxxx, Rusty Russell <rusty@xxxxxxxxxxxxxxx>, linux-kernel@xxxxxxxxxxxxxxx, dave.mccracken@xxxxxxxxxx, linux-mm@xxxxxxxxx, chris.mason@xxxxxxxxxx, sunil.mushran@xxxxxxxxxx, Avi Kivity <avi@xxxxxxxxxx>, Anthony Liguori <anthony@xxxxxxxxxxxxx>, Schwidefsky <schwidefsky@xxxxxxxxxx>, Marcelo Tosatti <mtosatti@xxxxxxxxxx>, alan@xxxxxxxxxxxxxxxxxxx, Balbir Singh <balbir@xxxxxxxxxxxxxxxxxx>
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Dan Magenheimer wrote:

I'm not saying either one is bad or good -- and I'm sure
each can be adapted to approximately deliver the value
of the other -- they are just approaching the same problem
from different perspectives.

Indeed.  Tmem and auto-ballooning have a simple mechanism,
but the policy required to make it work right could well
be too complex to ever get right.

CMM2 has a more complex mechanism, but the policy is
absolutely trivial.

CMM2 and auto-ballooning seem to give about similar
performance gains on zSystem.

I suspect that for Xen and KVM, we'll want to choose
for the approach that has the simpler policy, because
relying on different versions of different operating
systems to all get the policy of auto-ballooning or
tmem right is likely to result in bad interactions
between guests and other intractable issues.

All rights reversed.

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