On Wed, Oct 14, 2020 at 9:15 AM David Hildenbrand <david@xxxxxxxxxx> wrote: > > On 14.10.20 17:22, David Hildenbrand wrote: > > Hi everybody, > > > > Michal Privoznik played with "free page reporting" in QEMU/virtio-balloon > > with hugetlbfs and reported that this results in [1] > > > > 1. WARNING: CPU: 13 PID: 2438 at mm/page_counter.c:57 page_counter_uncharge+0x4b/0x5 > > > > 2. Any hugetlbfs allocations failing. (I assume because some accounting is wrong) > > > > > > QEMU with free page hinting uses fallocate(FALLOC_FL_PUNCH_HOLE) > > to discard pages that are reported as free by a VM. The reporting > > granularity is in pageblock granularity. So when the guest reports > > 2M chunks, we fallocate(FALLOC_FL_PUNCH_HOLE) one huge page in QEMU. > > > > I was also able to reproduce (also with virtio-mem, which similarly > > uses fallocate(FALLOC_FL_PUNCH_HOLE)) on latest v5.9 > > (and on v5.7.X from F32). > > > > Looks like something with fallocate(FALLOC_FL_PUNCH_HOLE) accounting > > is broken with cgroups. I did *not* try without cgroups yet. > > > > Any ideas? Hi David, I may be able to dig in and take a look. How do I reproduce this though? I just fallocate(FALLOC_FL_PUNCH_HOLE) one 2MB page in a hugetlb region? > > Just tried without the hugetlb controller, seems to work just fine. > > I'd like to note that > - The controller was not activated > - I had to compile the hugetlb controller out to make it work. > > -- > Thanks, > > David / dhildenb >
