On 11.02.20 15:07, Michael S. Tsirkin wrote: > On Tue, Feb 11, 2020 at 01:19:31PM +0100, David Hildenbrand wrote: >>>> >>>> Did you see the discussion regarding unifying handling of >>>> inflate/deflate/free_page_hinting_free_page_reporting, requested by >>>> Michael? I think free page reporting is special and shall be left alone. >>> >>> Not sure what do you mean by "left alone here". Could you clarify? >> >> Don't try to unify handling like I proposed below, because it's >> semantics are special. >> >>> >>>> VIRTIO_BALLOON_F_REPORTING is nothing but a more advanced inflate, right >>>> (sg, inflate based on size - not "virtio pages")? >>> >>> >>> Not exactly - it's also initiated by guest as opposed to host, and >>> not guided by the ballon size request set by the host. >> >> True, but AFAIKS you could use existing INFLATE/DEFLATE in a similar >> way. There is no way for the hypervisor to nack a request. The balloon >> size is not glued to inflate/deflate requests. The guests manually >> updates it. > > Hmm how isn't it? num_pages is the only way to inflate/deflate. Usually, guests are nice and respond to num_pages changes in an appropriate way, except: - Triggering deflate: Unload the driver. Suspend/hibernate. OOM. (+ Reboot, although that's special) - Triggering inflate + deflate: Simple balloon compaction / page migration. But that's not what I meant. "actual" is updated by the guest, not by the host. So the "actual balloon size" is set by the guest. It's not glued to inflation/deflation requests. "num_pages" is the host request. AFAIKs, the guest could inflate/deflate (esp. temporarily) and communicate via "actual" the actual balloon size as he sees it. > Spec also says: > The device is driven either by the receipt of a configuration change notification, or by changing guest memory > needs, such as performing memory compaction or responding to out of memory conditions. > > so ignoring compaction/oom (later is under-specified, not a good example > to follow) yes inflate/deflate are tied to host specified configuration Yes, "num_pages" is the host request. But I'd say the statement (esp. "the device is driven by") in the spec is rather weak. It does not explicitly state when inflation/deflation is allowed IMHO. -- Thanks, David / dhildenb
