Re: [RFC PATCH 07/10] memcg: use __mod_memcg_state in drain_obj_stock

[Sebastian Andrzej Siewior]

On 2025-03-14 11:27:40 [+0100], Vlastimil Babka wrote:
> On 3/14/25 07:15, Shakeel Butt wrote:
> > For non-PREEMPT_RT kernels, drain_obj_stock() is always called with irq
> > disabled, so we can use __mod_memcg_state() instead of
> > mod_memcg_state(). For PREEMPT_RT, we need to add memcg_stats_[un]lock
> > in __mod_memcg_state().
> > 
> > Signed-off-by: Shakeel Butt <shakeel.butt@xxxxxxxxx>
> 
> Maybe it'll make sense later but as of this patch itself it begs a question
> why put memcg_stats_lock()/unlock() in __mod_memcg_state itself and not just
> around the call in drain_obj_stock()?

The memcg_stats_lock() were introduce to protect the per-CPU counters
(vmstats_percpu) on PREEMPT_RT which are protected on !PREEMPT_RT by
disabling interrupts. Other modifier have this already except for
__mod_memcg_state() because mod_memcg_state() was the only user and
already disables interrupt for the operation.

Sebastian