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

[Vlastimil Babka]

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()?

> ---
>  mm/memcontrol.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index 3c4de384b5a0..dfe9c2eb7816 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -707,10 +707,12 @@ void __mod_memcg_state(struct mem_cgroup *memcg, enum memcg_stat_item idx,
>  	if (WARN_ONCE(BAD_STAT_IDX(i), "%s: missing stat item %d\n", __func__, idx))
>  		return;
>  
> +	memcg_stats_lock();
>  	__this_cpu_add(memcg->vmstats_percpu->state[i], val);
>  	val = memcg_state_val_in_pages(idx, val);
>  	memcg_rstat_updated(memcg, val);
>  	trace_mod_memcg_state(memcg, idx, val);
> +	memcg_stats_unlock();
>  }
>  
>  #ifdef CONFIG_MEMCG_V1
> @@ -2845,7 +2847,7 @@ static void drain_obj_stock(struct memcg_stock_pcp *stock)
>  
>  			memcg = get_mem_cgroup_from_objcg(old);
>  
> -			mod_memcg_state(memcg, MEMCG_KMEM, -nr_pages);
> +			__mod_memcg_state(memcg, MEMCG_KMEM, -nr_pages);
>  			memcg1_account_kmem(memcg, -nr_pages);
>  			if (!mem_cgroup_is_root(memcg))
>  				memcg_uncharge(memcg, nr_pages);