diff mbox series

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

Message ID 20250314061511.1308152-8-shakeel.butt@linux.dev (mailing list archive)
State New
Headers show
Series memcg: stock code cleanups | expand

Commit Message

Shakeel Butt March 14, 2025, 6:15 a.m. UTC
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@linux.dev>
---
 mm/memcontrol.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

Comments

Vlastimil Babka March 14, 2025, 10:27 a.m. UTC | #1
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@linux.dev>

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);
Sebastian Andrzej Siewior March 14, 2025, 11:38 a.m. UTC | #2
On 2025-03-13 23:15:08 [-0700], 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@linux.dev>

Reviewed-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>

Sebastian
Sebastian Andrzej Siewior March 14, 2025, 11:44 a.m. UTC | #3
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@linux.dev>
> 
> 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
diff mbox series

Patch

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);