On Fri 10-12-21 16:22:01, Sebastian Andrzej Siewior wrote:
[...]
I am sorry but I didn't get to read and digest the rest of the message
yet. Let me just point out this

The problematic part here is mem_cgroup_tree_per_node::lock which can
not be acquired with disabled interrupts on PREEMPT_RT.  The "locking
scope" is not always clear to me.  Also, if it is _just_ the counter,
then we might solve this differently.

I do not think you should be losing sleep over soft limit reclaim. This
is certainly not something to be used for RT workloads and rather than
touching that code I think it makes some sense to simply disallow soft
limit with RT enabled (i.e. do not allow to set any soft limit).
-- 
Michal Hocko
SUSE Labs