Messages in this thread | | | From | Waiman Long <> | Subject | Re: [PATCH v3 2/5] mm/memcg: Introduce obj_cgroup_uncharge_mod_state() | Date | Thu, 15 Apr 2021 12:35:45 -0400 |
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On 4/15/21 12:30 PM, Johannes Weiner wrote: > 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. > That will also work. However, the reason I did that was because of patch 5 in the series. I could put the get_obj_stock() and put_obj_stock() code in slab.h and allowed them to be used directly in various places, but hiding in one function is easier.
Anyway, I can change the patch if you think that is the right way.
Cheers, Longman
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