On Fri, Jun 16, 2017 at 04:20:02PM +0200, David Hildenbrand wrote: > Hi, > > this is an idea that is based on Andrea Arcangeli's original idea to > host enforce guest access to memory given up using virtio-balloon using > userfaultfd in the hypervisor. While looking into the details, I > realized that host-enforcing virtio-balloon would result in way too many > problems (mainly backwards compatibility) and would also have some > conceptual restrictions that I want to avoid. So I developed the idea of > virtio-mem - "paravirtualized memory". Thanks! I went over this quickly, will read some more in the coming days. I would like to ask for some clarifications on one part meanwhile: > Q: Why not reuse virtio-balloon? > > A: virtio-balloon is for cooperative memory management. It has a fixed > page size We are fixing that with VIRTIO_BALLOON_F_PAGE_CHUNKS btw. I would appreciate you looking into that patchset. > and will deflate in certain situations. What does this refer to? > Any change we > introduce will break backwards compatibility. Why does this have to be the case? > virtio-balloon was not > designed to give guarantees. Nobody can hinder the guest from > deflating/reusing inflated memory. Reusing without deflate is forbidden with TELL_HOST, right? > In addition, it might make perfect > sense to have both, virtio-balloon and virtio-mem at the same time, > especially looking at the DEFLATE_ON_OOM or STATS features of > virtio-balloon. While virtio-mem is all about guarantees, virtio- > balloon is about cooperation. Thanks, and I intend to look more into this next week. -- MST
