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Subject[PATCH V3 7/8] memcg: disable memcg page stat accounting code when not in use
Date
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);
mem_cgroup_put(memcg);
}

--
1.7.9.5


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