Re: [PATCH] mm/memcontrol: Disable on PREEMPT_RT

[Sebastian Andrzej Siewior <bigeasy-hfZtesqFncYOwBW4kG4KsQ@public.gmane.org>]

On 2021-12-13 11:08:26 [+0100], Michal Hocko wrote:
> 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).

Okay. So instead of disabling it entirely you suggest I should take
another stab at it? Okay. Disabling softlimit, where should I start with
it? Should mem_cgroup_write() for RES_SOFT_LIMIT always return an error
or something else?
In the meantime I try to swap in my memcg memory…

Sebastian