Re: [PATCH v3 2/5] mm/memcg: Introduce obj_cgroup_uncharge_mod_state()

[Masayoshi Mizuma <msys.mizuma@gmail.com>]

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.
> 
> Signed-off-by: Waiman Long <longman@redhat.com>
> Reviewed-by: Shakeel Butt <shakeelb@google.com>
> Acked-by: Roman Gushchin <guro@fb.com>
> ---
>  include/linux/memcontrol.h |  2 ++
>  mm/memcontrol.c            | 31 +++++++++++++++++++++++++++----
>  mm/percpu.c                |  9 ++-------
>  mm/slab.h                  |  6 +++---
>  4 files changed, 34 insertions(+), 14 deletions(-)
> 
> diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
> index 95f12996e66c..6890f999c1a3 100644
> --- a/include/linux/memcontrol.h
> +++ b/include/linux/memcontrol.h
> @@ -1592,6 +1592,8 @@ struct obj_cgroup *get_obj_cgroup_from_current(void);
>  
>  int obj_cgroup_charge(struct obj_cgroup *objcg, gfp_t gfp, size_t size);
>  void obj_cgroup_uncharge(struct obj_cgroup *objcg, size_t size);
> +void obj_cgroup_uncharge_mod_state(struct obj_cgroup *objcg, size_t size,
> +				   struct pglist_data *pgdat, int idx);
>  
>  extern struct static_key_false memcg_kmem_enabled_key;
>  
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index d66e1e38f8ac..b19100c68aa0 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -3225,12 +3225,9 @@ static bool obj_stock_flush_required(struct memcg_stock_pcp *stock,
>  	return false;
>  }
>  
> -static void refill_obj_stock(struct obj_cgroup *objcg, unsigned int nr_bytes)
> +static void __refill_obj_stock(struct obj_cgroup *objcg, unsigned int nr_bytes)
>  {
>  	struct memcg_stock_pcp *stock;
> -	unsigned long flags;
> -
> -	local_irq_save(flags);
>  
>  	stock = this_cpu_ptr(&memcg_stock);
>  	if (stock->cached_objcg != objcg) { /* reset if necessary */
> @@ -3243,7 +3240,14 @@ static void refill_obj_stock(struct obj_cgroup *objcg, unsigned int nr_bytes)
>  
>  	if (stock->nr_bytes > PAGE_SIZE)
>  		drain_obj_stock(stock);
> +}
> +
> +static void refill_obj_stock(struct obj_cgroup *objcg, unsigned int nr_bytes)
> +{
> +	unsigned long flags;
>  
> +	local_irq_save(flags);
> +	__refill_obj_stock(objcg, nr_bytes);
>  	local_irq_restore(flags);
>  }
>  
> @@ -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)
> +{
> +	unsigned long flags;
> +	struct mem_cgroup *memcg;
> +	struct lruvec *lruvec = NULL;
> +
> +	local_irq_save(flags);
> +	__refill_obj_stock(objcg, size);
> +
> +	rcu_read_lock();
> +	memcg = obj_cgroup_memcg(objcg);
> +	if (pgdat)
> +		lruvec = mem_cgroup_lruvec(memcg, pgdat);
> +	__mod_memcg_lruvec_state(memcg, lruvec, idx, -(int)size);
> +	rcu_read_unlock();
> +	local_irq_restore(flags);
> +}
> +
>  #endif /* CONFIG_MEMCG_KMEM */
>  
>  /*
> diff --git a/mm/percpu.c b/mm/percpu.c
> index 23308113a5ff..fd7aad6d7f90 100644
> --- a/mm/percpu.c
> +++ b/mm/percpu.c
> @@ -1631,13 +1631,8 @@ static void pcpu_memcg_free_hook(struct pcpu_chunk *chunk, int off, size_t size)
>  	objcg = chunk->obj_cgroups[off >> PCPU_MIN_ALLOC_SHIFT];
>  	chunk->obj_cgroups[off >> PCPU_MIN_ALLOC_SHIFT] = NULL;
>  
> -	obj_cgroup_uncharge(objcg, size * num_possible_cpus());
> -
> -	rcu_read_lock();
> -	mod_memcg_state(obj_cgroup_memcg(objcg), MEMCG_PERCPU_B,
> -			-(size * num_possible_cpus()));
> -	rcu_read_unlock();
> -
> +	obj_cgroup_uncharge_mod_state(objcg, size * num_possible_cpus(),
> +				      NULL, MEMCG_PERCPU_B);
>  	obj_cgroup_put(objcg);
>  }
>  
> diff --git a/mm/slab.h b/mm/slab.h
> index bc6c7545e487..677cdc52e641 100644
> --- a/mm/slab.h
> +++ b/mm/slab.h
> @@ -366,9 +366,9 @@ static inline void memcg_slab_free_hook(struct kmem_cache *s_orig,
>  			continue;
>  
>  		objcgs[off] = NULL;
> -		obj_cgroup_uncharge(objcg, obj_full_size(s));
> -		mod_objcg_state(objcg, page_pgdat(page), cache_vmstat_idx(s),
> -				-obj_full_size(s));
> +		obj_cgroup_uncharge_mod_state(objcg, obj_full_size(s),
> +					      page_pgdat(page),
> +					      cache_vmstat_idx(s));
>  		obj_cgroup_put(objcg);
>  	}
>  }
> -- 
> 2.18.1
> 

Please feel free to add:

Tested-by: Masayoshi Mizuma <m.mizuma@jp.fujitsu.com>

Thanks!
Masa