On Wed, Jul 17, 2019 at 04:10:47PM +0200, David Hildenbrand wrote: > On 17.07.19 13:20, Michael S. Tsirkin wrote: > > Wei, others, > > > > ATM virtio_balloon_shrinker_scan will only get registered > > when deflate on oom feature bit is set. > > > > Not sure whether that's intentional. Assuming it is: > > > > virtio_balloon_shrinker_scan will try to locate and free > > pages that are processed by host. > > The above seems broken in several ways: > > - count ignores the free page list completely > > - if free pages are being reported, pages freed > > by shrinker will just get re-allocated again > > Trying to answer your questions (not sure if I fully understood what you > mean) > > virtio_balloon_shrinker_scan() will not be called due to inflation > requests (balloon_page_alloc()). It will be called whenever the system > is OOM, e.g., when starting a new application. > > I assume you were expecting the shrinker getting called due to > balloon_page_alloc(). however, that is not the case as we pass > "__GFP_NORETRY". Right but it's possible we exhaust all memory, then someone else asks for a single page and that invokes the shrinker. > > To test, something like: > > 1. Start a VM with > > -device virtio-balloon-pci,deflate-on-oom=true > > 2. Inflate the balloon, e.g., > > QMP: balloon 1024 > QMP: info balloon > -> 1024 > > See how "MemTotal" in /proc/meminfo in the guest won't change > > 3. Run a workload that exhausts memory in the guest (OOM). > > See how the balloon was automatically deflated > > QMP: info balloon > -> Something bigger than 1024 > > > Not sure if it is broken, last time I played with it, it worked, but > that was ~1-2 years ago. > > -- > > Thanks, > > David / dhildenb Sorry I was unclear. The question was about VIRTIO_BALLOON_F_FREE_PAGE_HINT specifically. -- MST
