Re: [PATCH v2 2/4] mm/memcg: Disable threshold event handlers on PREEMPT_RT

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On Fri, Feb 11, 2022 at 11:35:35PM +0100, Sebastian Andrzej Siewior wrote:
> During the integration of PREEMPT_RT support, the code flow around
> memcg_check_events() resulted in `twisted code'. Moving the code around
> and avoiding then would then lead to an additional local-irq-save
> section within memcg_check_events(). While looking better, it adds a
> local-irq-save section to code flow which is usually within an
> local-irq-off block on non-PREEMPT_RT configurations.
> 
> The threshold event handler is a deprecated memcg v1 feature. Instead of
> trying to get it to work under PREEMPT_RT just disable it. There should
> be no users on PREEMPT_RT. From that perspective it makes even less
> sense to get it to work under PREEMPT_RT while having zero users.
> 
> Make memory.soft_limit_in_bytes and cgroup.event_control return
> -EOPNOTSUPP on PREEMPT_RT. Make an empty memcg_check_events() and
> memcg_write_event_control() which return only -EOPNOTSUPP on PREEMPT_RT.
> Document that the two knobs are disabled on PREEMPT_RT.
> 
> Suggested-by: Michal Hocko <mhocko@xxxxxxxxxx>
> Suggested-by: Michal Koutný <mkoutny@xxxxxxxx>
> Signed-off-by: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx>

Acked-by: Johannes Weiner <hannes@xxxxxxxxxxx>





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