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

[Waiman Long <longman@redhat.com>]

On 12/7/21 10:52, Sebastian Andrzej Siewior wrote:
> From: Thomas Gleixner <tglx@linutronix.de>
>
> MEMCG has a few constructs which are not compatible with PREEMPT_RT's
> requirements. This includes:
> - relying on disabled interrupts from spin_lock_irqsave() locking for
>    something not related to lock itself (like the per-CPU counter).
>
> - explicitly disabling interrupts and acquiring a spinlock_t based lock
>    like in memcg_check_events() -> eventfd_signal().
>
> - explicitly disabling interrupts and freeing memory like in
>    drain_obj_stock() -> obj_cgroup_put() -> obj_cgroup_release() ->
>    percpu_ref_exit().
>
> Commit 559271146efc ("mm/memcg: optimize user context object stock
> access") continued to optimize for the CPU local access which
> complicates the PREEMPT_RT locking requirements further.
>
> Disable MEMCG on PREEMPT_RT until the whole situation can be evaluated
> again.

Disabling MEMCG for PREEMPT_RT may be too drastic a step to take. For 
commit 559271146efc ("mm/memcg: optimize user context object stock 
access"), I can modify it to disable the optimization for PREEMPT_RT.

Cheers,
Longman


> [ bigeasy: commit description. ]
>
> Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
> Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
> ---
>   init/Kconfig |    1 +
>   1 file changed, 1 insertion(+)
>
> --- a/init/Kconfig
> +++ b/init/Kconfig
> @@ -943,6 +943,7 @@ config PAGE_COUNTER
>   
>   config MEMCG
>   	bool "Memory controller"
> +	depends on !PREEMPT_RT
>   	select PAGE_COUNTER
>   	select EVENTFD
>   	help
>