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 > > I was unable to make this part of code behave in any reasonable > way - was shrinker usage tested? What's a good way to test that? > > Thanks! > Some companies are using deflate-on-oom for some kind of "auto ballooning" approach, although I don't think it's a good idea. In these scenarios, the total ramsize (cat /proc/meminfo) will not change on inflation/deflation. So from a system POV, inflated memory is simply allocated memory without affecting the total memory. VMs will automatically "reclaim" inflated memory when they need it - which is usually not what hypervisors want (especially when talking about using ballooning for memory hotunplug). So yes, it makes perfect sense that the shrinker is only registered for deflate-on-oom. -- Thanks, David / dhildenb
