Re: [PATCH V3 7/8] memcg: disable memcg page stat accounting code when not in use

[Kamezawa Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>]

(2012/12/26 2:27), Sha Zhengju wrote:
> From: Sha Zhengju <handai.szj@taobao.com>
> 
> It's inspired by a similar optimization from Glauber Costa
> (memcg: make it suck faster; https://lkml.org/lkml/2012/9/25/154).
> Here we use jump label to patch the memcg page stat accounting code
> in or out when not used. when the first non-root memcg comes to
> life the code is patching in otherwise it is out.
> 
> Signed-off-by: Sha Zhengju <handai.szj@taobao.com>
> ---
>   include/linux/memcontrol.h |    9 +++++++++
>   mm/memcontrol.c            |    8 ++++++++
>   2 files changed, 17 insertions(+)
> 
> diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
> index 1d22b81..3c4430c 100644
> --- a/include/linux/memcontrol.h
> +++ b/include/linux/memcontrol.h
> @@ -56,6 +56,9 @@ struct mem_cgroup_reclaim_cookie {
>   };
>   
>   #ifdef CONFIG_MEMCG
> +
> +extern struct static_key memcg_in_use_key;
> +
>   /*
>    * All "charge" functions with gfp_mask should use GFP_KERNEL or
>    * (gfp_mask & GFP_RECLAIM_MASK). In current implementatin, memcg doesn't
> @@ -158,6 +161,9 @@ extern atomic_t memcg_moving;
>   static inline void mem_cgroup_begin_update_page_stat(struct page *page,
>   					bool *locked, unsigned long *flags)
>   {
> +	if (!static_key_false(&memcg_in_use_key))
> +		return;
> +
>   	if (mem_cgroup_disabled())
>   		return;
>   	rcu_read_lock();
> @@ -171,6 +177,9 @@ void __mem_cgroup_end_update_page_stat(struct page *page,
>   static inline void mem_cgroup_end_update_page_stat(struct page *page,
>   					bool *locked, unsigned long *flags)
>   {
> +	if (!static_key_false(&memcg_in_use_key))
> +		return;
> +
>   	if (mem_cgroup_disabled())
>   		return;
>   	if (*locked)
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index 0cb5187..a2f73d7 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -531,6 +531,8 @@ enum res_type {
>   #define MEM_CGROUP_RECLAIM_SHRINK_BIT	0x1
>   #define MEM_CGROUP_RECLAIM_SHRINK	(1 << MEM_CGROUP_RECLAIM_SHRINK_BIT)
>   
> +struct static_key memcg_in_use_key;
> +
>   static void mem_cgroup_get(struct mem_cgroup *memcg);
>   static void mem_cgroup_put(struct mem_cgroup *memcg);
>   
> @@ -2226,6 +2228,9 @@ void mem_cgroup_update_page_stat(struct page *page,
>   	struct page_cgroup *pc = lookup_page_cgroup(page);
>   	unsigned long uninitialized_var(flags);
>   
> +	if (!static_key_false(&memcg_in_use_key))
> +		return;
> +
>   	if (mem_cgroup_disabled())
>   		return;
>   
> @@ -6340,6 +6345,8 @@ mem_cgroup_css_alloc(struct cgroup *cont)
>   		parent = mem_cgroup_from_cont(cont->parent);
>   		memcg->use_hierarchy = parent->use_hierarchy;
>   		memcg->oom_kill_disable = parent->oom_kill_disable;
> +
> +		static_key_slow_inc(&memcg_in_use_key);
>   	}
>   
>   	if (parent && parent->use_hierarchy) {
> @@ -6407,6 +6414,7 @@ static void mem_cgroup_css_free(struct cgroup *cont)
>   	kmem_cgroup_destroy(memcg);
>   
>   	memcg_dangling_add(memcg);
> +	static_key_slow_dec(&memcg_in_use_key);

Hmm. I think this part should be folded into disarm_static_keys().

Thanks,
-Kame




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