On Thu, Feb 06, 2020 at 10:05:43AM +0100, David Hildenbrand wrote: > >> commit bf50e69f63d21091e525185c3ae761412be0ba72 > >> Author: Dave Hansen <dave@xxxxxxxxxxxxxxxxxx> > >> Date: Thu Apr 7 10:43:25 2011 -0700 > >> > >> virtio balloon: kill tell-host-first logic > >> > >> The virtio balloon driver has a VIRTIO_BALLOON_F_MUST_TELL_HOST > >> feature bit. Whenever the bit is set, the guest kernel must > >> always tell the host before we free pages back to the allocator. > >> Without this feature, we might free a page (and have another > >> user touch it) while the hypervisor is unprepared for it. > >> > >> But, if the bit is _not_ set, we are under no obligation to > >> reverse the order; we're under no obligation to do _anything_. > >> As of now, qemu-kvm defines the bit, but doesn't set it. > > > > Well this is not what the spec says in the end. > > I didn't check the spec, maybe I should do that :) > > > To continue that commit message: > > > > This patch makes the "tell host first" logic the only case. This > > should make everybody happy, and reduce the amount of untested or > > untestable code in the kernel. > > Yeah, but this comment explains that the current deflate is only in > place, because it makes the code simpler (to support both cases). Of > course, doing the deflate might result in performance improvements. > (e.g., MADV_WILLNEED) > > > > > you can try proposing the change to the virtio TC, see what do others > > think. > > We can just drop the comment from this patch for now. The tell_host host > not be an issue AFAIKS. I guess it's a good idea. > -- > Thanks, > > David / dhildenb
