On Tue, Apr 13, 2021 at 09:20:24PM -0400, Waiman Long wrote: > In memcg_slab_free_hook()/pcpu_memcg_free_hook(), obj_cgroup_uncharge() > is followed by mod_objcg_state()/mod_memcg_state(). Each of these > function call goes through a separate irq_save/irq_restore cycle. That > is inefficient. Introduce a new function obj_cgroup_uncharge_mod_state() > that combines them with a single irq_save/irq_restore cycle. > > @@ -3292,6 +3296,25 @@ void obj_cgroup_uncharge(struct obj_cgroup *objcg, size_t size) > refill_obj_stock(objcg, size); > } > > +void obj_cgroup_uncharge_mod_state(struct obj_cgroup *objcg, size_t size, > + struct pglist_data *pgdat, int idx) The optimization makes sense. But please don't combine independent operations like this into a single function. It makes for an unclear parameter list, it's a pain in the behind to change the constituent operations later on, and it has a habit of attracting more random bools over time. E.g. what if the caller already has irqs disabled? What if it KNOWS that irqs are enabled and it could use local_irq_disable() instead of save? Just provide an __obj_cgroup_uncharge() that assumes irqs are disabled, combine with the existing __mod_memcg_lruvec_state(), and bubble the irq handling up to those callsites which know better.
