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xen-devel
RE: [Xen-devel] Re: [RFC PATCH 0/4] (Take 2): transcendent memory ("tmem
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To: |
Avi Kivity <avi@xxxxxxxxxx> |
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Subject: |
RE: [Xen-devel] Re: [RFC PATCH 0/4] (Take 2): transcendent memory ("tmem") for Linux |
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From: |
Dan Magenheimer <dan.magenheimer@xxxxxxxxxx> |
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Date: |
Sun, 12 Jul 2009 13:39:07 -0700 (PDT) |
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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, Anthony, linux-mm@xxxxxxxxx, sunil.mushran@xxxxxxxxxx, alan@xxxxxxxxxxxxxxxxxxx, Liguori <anthony@xxxxxxxxxxxxx>, Schwidefsky <schwidefsky@xxxxxxxxxx>, Marcelo Tosatti <mtosatti@xxxxxxxxxx>, chris.mason@xxxxxxxxxx, Balbir Singh <balbir@xxxxxxxxxxxxxxxxxx> |
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Sun, 12 Jul 2009 13:40:39 -0700 |
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> CMM2 and tmem are not any different in this regard; both require OS
> modification, and both make information available to the
> hypervisor. In
> fact CMM2 is much more intrusive (but on the other hand provides much
> more information).
>
> > For those that believe it will be pervasive in the
> > future, finding the right balance is a critical step
> > in operating system evolution.
>
> You're arguing for CMM2 here IMO.
I'm arguing that both are a good thing and a step in
the right direction. In some ways, tmem is a bigger
step and in some ways CMM2 is a bigger step.
> My take on this is that precache (predecache?) / preswap can be
> implemented even without tmem by using write-through backing for the
> virtual disk. For swap this is actually slight;y more efficient than
> tmem preswap, for preuncache slightly less efficient (since
> there will
> be some double caching). So I'm more interested in other use
> cases of tmem/CMM2.
>
> Right, the transient uses of tmem when applied to disk objects
> (swap/pagecache) are very similar to disk caches. Which is
> why you can
> get a very similar effect when caching your virtual disks;
> this can be
> done without any guest modification.
Write-through backing and virtual disk cacheing offer a
similar effect, but it is far from the same.
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