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

Dan Magenheimer
2009-07-12T20:41:06Z

> 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.