[Devel] Re: [PATCH v3 10/13] memcg: use static branches when code not in use

[Michal Hocko]

On Tue 18-09-12 18:04:07, Glauber Costa wrote:
[...]
>  include/linux/memcontrol.h |  4 +++-
>  mm/memcontrol.c            | 26 ++++++++++++++++++++++++--
>  2 files changed, 27 insertions(+), 3 deletions(-)
> 
> diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
> index 82ede9a..4ec9fd5 100644
> --- a/include/linux/memcontrol.h
> +++ b/include/linux/memcontrol.h
> @@ -22,6 +22,7 @@
>  #include <linux/cgroup.h>
>  #include <linux/vm_event_item.h>
>  #include <linux/hardirq.h>
> +#include <linux/jump_label.h>
>  
>  struct mem_cgroup;
>  struct page_cgroup;
> @@ -401,9 +402,10 @@ struct sock;
>  void sock_update_memcg(struct sock *sk);
>  void sock_release_memcg(struct sock *sk);
>  
> +extern struct static_key memcg_kmem_enabled_key;
>  static inline bool memcg_kmem_enabled(void)
>  {
> -	return true;
> +	return static_key_false(&memcg_kmem_enabled_key);
>  }
>  
>  extern bool __memcg_kmem_newpage_charge(gfp_t gfp, struct mem_cgroup **memcg,
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index 720e4bb..aada601 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -467,6 +467,8 @@ struct mem_cgroup *mem_cgroup_from_css(struct cgroup_subsys_state *s)
>  #include <net/sock.h>
>  #include <net/ip.h>
>  
> +struct static_key memcg_kmem_enabled_key;
> +
>  static bool mem_cgroup_is_root(struct mem_cgroup *memcg);
>  static int memcg_charge_kmem(struct mem_cgroup *memcg, gfp_t gfp, u64 size);
>  static void memcg_uncharge_kmem(struct mem_cgroup *memcg, u64 size);
> @@ -624,6 +626,16 @@ void __memcg_kmem_uncharge_page(struct page *page, int order)
>  	WARN_ON(mem_cgroup_is_root(memcg));
>  	memcg_uncharge_kmem(memcg, PAGE_SIZE << order);
>  }
> +
> +static void disarm_kmem_keys(struct mem_cgroup *memcg)
> +{
> +	if (memcg_kmem_is_accounted(memcg))
> +		static_key_slow_dec(&memcg_kmem_enabled_key);
> +}
> +#else
> +static void disarm_kmem_keys(struct mem_cgroup *memcg)
> +{
> +}
>  #endif /* CONFIG_MEMCG_KMEM */
>  
>  #if defined(CONFIG_INET) && defined(CONFIG_MEMCG_KMEM)
> @@ -639,6 +651,12 @@ static void disarm_sock_keys(struct mem_cgroup *memcg)
>  }
>  #endif
>  
> +static void disarm_static_keys(struct mem_cgroup *memcg)
> +{
> +	disarm_sock_keys(memcg);
> +	disarm_kmem_keys(memcg);
> +}
> +
>  static void drain_all_stock_async(struct mem_cgroup *memcg);
>  
>  static struct mem_cgroup_per_zone *
> @@ -4131,7 +4149,11 @@ static void memcg_update_kmem_limit(struct mem_cgroup *memcg, u64 val)
>  	 */
>  	mutex_lock(&set_limit_mutex);
>  	if ((val != RESOURCE_MAX) && memcg_kmem_set_active(memcg)) {
> -
> +		/*
> +		 * Once the static branch is enabled it will only be
> +		 * disabled when the last reference to memcg is gone.
> +		 */
> +		static_key_slow_inc(&memcg_kmem_enabled_key);

I guess the reason why we do not need to inc also for children is that
we do not inherit kmem_accounted, right?

>  		mem_cgroup_get(memcg);
>  
>  		for_each_mem_cgroup_tree(iter, memcg) {
> @@ -5066,7 +5088,7 @@ static void free_work(struct work_struct *work)
>  	 * to move this code around, and make sure it is outside
>  	 * the cgroup_lock.
>  	 */
> -	disarm_sock_keys(memcg);
> +	disarm_static_keys(memcg);
>  	if (size < PAGE_SIZE)
>  		kfree(memcg);
>  	else
> -- 
> 1.7.11.4
> 
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-- 
Michal Hocko
SUSE Labs