Re: [PATCH 2/9] memcg: decouple drain_obj_stock from local stock

[Roman Gushchin]

On Sat, Mar 15, 2025 at 10:49:23AM -0700, Shakeel Butt wrote:
> Currently drain_obj_stock() can potentially call __refill_stock which
> accesses local cpu stock and thus requires memcg stock's local_lock.
> However if we look at the code paths leading to drain_obj_stock(), there
> is never a good reason to refill the memcg stock at all from it.
> 
> At the moment, drain_obj_stock can be called from reclaim, hotplug cpu
> teardown, mod_objcg_state() and refill_obj_stock(). For reclaim and
> hotplug there is no need to refill. For the other two paths, most
> probably the newly switched objcg would be used in near future and thus
> no need to refill stock with the older objcg.
> 
> In addition, __refill_stock() from drain_obj_stock() happens on rare
> cases, so performance is not really an issue. Let's just uncharge
> directly instead of refill which will also decouple drain_obj_stock from
> local cpu stock and local_lock requirements.
> 
> Signed-off-by: Shakeel Butt <shakeel.butt@xxxxxxxxx>
> Acked-by: Vlastimil Babka <vbabka@xxxxxxx>

Reviewed-by: Roman Gushchin <roman.gushchin@xxxxxxxxx>