Depending on the workloads, some customers are hitting problem with OOM killer activated and the system locking up for a rather long period of time. For example, 

 1) BZ #1853862 - [mm] System locked up for over an hour during memory reclaim
 2) BZ #1857446 - ARO/Azure: excessive pod memory allocation causes node lockup 

There are two different problem here:

 1) The workload is consuming memory faster than the system can recover through memory reclaim.
 2) The systems seems to lockup when OOM killer was invoked to kill some tasks.

The first problem can be addressed if cgroup v2 is used by the customer as the following upstream commit and its derivatives can help to prevent the processes
from consuming memory too fast.

commit 0e4b01df865935007bd712cbc8e7299005b28894
Author: Chris Down <chris>
Date:   Mon, 23 Sep 2019 15:34:55 -0700

    mm, memcg: throttle allocators when failing reclaim over memory.high

However, cgroup v1 is still the default. Even though we are going to switch to cgroup v2 as the default soon, it takes time for customers to do the migration.

For existing cgroup v1 customers, we need to improve the memory reclaim and OOM handling code to a more updated code base of v5.6. Hopefully that can help to alleviate the problem.

For the second lockup problem, it is not clear what causes it. Dong Hai is investigating the core dump report in BZ #1853862 to find some clue. If a reproducer can be found, it will help us to locate the problem area more quickly. More work still need to be done.

-Longman