[Spice-devel] viewing continuous guest virtual memory as continuous in qemu
alevy at redhat.com
Tue Oct 11 05:21:17 PDT 2011
On Tue, Oct 11, 2011 at 01:28:12PM +0200, Gerd Hoffmann wrote:
> >AFAIU this works only when the guest allocates a continuous range of
> >physical pages. This is a large requirement from the guest, which I'd
> >like to drop.
> Is it? The world is moving to huge pages, with all the stuff needed
> for it like moving around userspace pages to compact memory and make
> huge page allocation easier. I think these days it is alot easier
> to allocate 2M of continuous physical memory than it used to be a
> few years ago. At least on linux, dunno about windows.
> When allocating stuff at boot time (say qxl kms driver) allocating
> even larger chunks shouldn't be a big issue. And having a single
> big guest memory chunk, then register that as qxl memory slot is
> what works best with the existing interfaces I guess.
Right, this would work. I was trying to avoid claiming a large chunk up
front. I was also trying to avoid having our own allocator, although I
think that's not really a problem (can be replaced with an in kernel
> Another option we can think about is a 64bit PCI bar for the
> surfaces which can be moved out of the low 4G.
I heard this suggested by Avi, so this would allow us to allocate a
large chunk without requiring any memory hole?
> >So I would like to have the guest use a regular
> >allocator, generating for instance two sequential pages in virtual
> >memory that are scattered in physical memory. Those two physical
> >guest page addresses (gp1 and gp2) correspond to two host virtual
> >memory addresses (hv1, hv2). I would now like to provide to
> >spice-server a single virtual address p that maps to those two pages
> >in sequence.
> Playing mapping tricks like this doesn't come for free. When doing
> it this way we probaby still want to register a big chunk of memory
> as qxl memory slot so we have the mapping cost only once, not for
> each and every surface we create and destroy.
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