Re: Balloon device in qemu?

[Andrea Arcangeli <andrea@qumranet.com>]

On Mon, Aug 04, 2008 at 10:32:58AM +0200, Gerd Hoffmann wrote:
> #define KVM_CAP_SYNC_MMU 16  /* Changes to host mmap are reflected in
> guest */
> 
> This one I guess ...

That doesn't currently tell if kvm is using mmu notifiers though,
because it's set unconditionally. If we want to use it to tell if kvm
is using mmu notifiers we've to wrap it around an #ifdef or to use the
awk hack, which is trivial to add.

I'm more worried about the fact that with Anthony's plan ballooning
will be unusable for a long while on enterprise distros, as it will
take a while before they run on a >=2.6.27 kernel. So I wonder if a
compact layer is worth it. But surely initially we can modify
KVM_CAP_SYNC_MMU to not be set if kernel isn't compiled with
CONFIG_MMU_NOTIFIER=y and we can add the compact layer later if needed.