On Mon 17-09-18 09:04:02, Stefan Priebe - Profihost AG wrote:

Hi,

i had multiple memory stalls this weekend again. All kvm processes where
spinning trying to get > 100% CPU and i was not able to even login to
ssh. After 5-10 minutes i was able to login.

There were about 150GB free mem on the host.

Relevant settings (no local storage involved):
        vm.dirty_background_ratio:
            3
        vm.dirty_ratio:
            10
        vm.min_free_kbytes:
            10567004

# cat /sys/kernel/mm/transparent_hugepage/defrag
always defer [defer+madvise] madvise never

# cat /sys/kernel/mm/transparent_hugepage/enabled
[always] madvise never

After that i had the following traces on the host node:
https://pastebin.com/raw/0VhyQmAv

I would suggest reporting this in a new email thread. I would also
recommend to CC kvm guys (see MAINTAINERS file in the kernel source
tree) and trace qemu/kvm processes to see what they are doing at the
time when you see the stall.
-- 
Michal Hocko
SUSE Labs