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
