Re: [PATCH v2 1/4] mm/memcg: Revert ("mm/memcg: optimize user context object stock access")

[Johannes Weiner <hannes-druUgvl0LCNAfugRpC6u6w@public.gmane.org>]

On Fri, Feb 11, 2022 at 11:35:34PM +0100, Sebastian Andrzej Siewior wrote:
> From: Michal Hocko <mhocko-IBi9RG/b67k@public.gmane.org>
> 
> The optimisation is based on a micro benchmark where local_irq_save() is
> more expensive than a preempt_disable(). There is no evidence that it is
> visible in a real-world workload and there are CPUs where the opposite is
> true (local_irq_save() is cheaper than preempt_disable()).
> 
> Based on micro benchmarks, the optimisation makes sense on PREEMPT_NONE
> where preempt_disable() is optimized away. There is no improvement with
> PREEMPT_DYNAMIC since the preemption counter is always available.
> 
> The optimization makes also the PREEMPT_RT integration more complicated
> since most of the assumption are not true on PREEMPT_RT.
> 
> Revert the optimisation since it complicates the PREEMPT_RT integration
> and the improvement is hardly visible.
> 
> [ bigeasy: Patch body around Michal's diff ]
> 
> Link: https://lore.kernel.org/all/YgOGkXXCrD%2F1k+p4-2MMpYkNvuYDjFM9bn6wA6Q@public.gmane.org
> Link: https://lkml.kernel.org/r/YdX+INO9gQje6d0S-hfZtesqFncYOwBW4kG4KsQ@public.gmane.org
> Signed-off-by: Michal Hocko <mhocko-IBi9RG/b67k@public.gmane.org>
> Signed-off-by: Sebastian Andrzej Siewior <bigeasy-hfZtesqFncYOwBW4kG4KsQ@public.gmane.org>

Acked-by: Johannes Weiner <hannes-druUgvl0LCNAfugRpC6u6w@public.gmane.org>