RE: Memory de-duplication (Persistent pages)

[Dan Magenheimer <dan.magenheimer@oracle.com>]

> > While I know nothing about OpenCL other than a quick read
> > in wikipedia, I suspect that putting an OpenCL abstraction
> > layer in the hypervisor is not going to be popular with
> > Xen developers. :-)
> 
> There's nothing to say that the GPU code has to live in the hypervisor.
> A tools domain that was already scanning for duplicates in other
> domains' memory (or for that matter in block traffic) could use
> whatever
> GPU resources it liked.
> 
> Even in the tmem case a domain could be given read-only access to the
> tmem pool (er, if IOMMUs support such a thing, which I don't recall off
> the top of my head) and supply hints to the hypervisor.  That way the
> hypervisor would still be scanning with the CPU but only on pages where
> it was likely to succeed.

While I agree this is not impossible, tmem is designed to
be highly concurrent and the data structures manage potentially
millions of pages with thousands of pages put/got per vcpu
per domain per second.  I think just trying to deal with the
locking from a tools domain would negate any performance gain
from a GPU.  And, in any case, the overhead of tmem deduplication
is unlikely to be large enough (except possibly in contrived
cases) to be worth the work.