memcg: cpu hotplug aware percpu count updates
Now, memcgroup's per cpu coutner uses for_each_possible_cpu() to get the
value. It's better to use for_each_online_cpu() and a cpu hotplug
handler.
This patch only handles statistics counter. MEM_CGROUP_ON_MOVE will be
handled in another patch.
Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 5e7a14d..31a1d3b 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -89,7 +89,9 @@
MEM_CGROUP_STAT_PGPGIN_COUNT, /* # of pages paged in */
MEM_CGROUP_STAT_PGPGOUT_COUNT, /* # of pages paged out */
MEM_CGROUP_STAT_SWAPOUT, /* # of pages, swapped out */
- MEM_CGROUP_EVENTS, /* incremented at every pagein/pageout */
+ MEM_CGROUP_STAT_DATA, /* end of data requires synchronization */
+ /* incremented at every pagein/pageout */
+ MEM_CGROUP_EVENTS = MEM_CGROUP_STAT_DATA,
MEM_CGROUP_ON_MOVE, /* someone is moving account between groups */
MEM_CGROUP_STAT_NSTATS,
@@ -255,6 +257,12 @@
* percpu counter.
*/
struct mem_cgroup_stat_cpu *stat;
+ /*
+ * used when a cpu is offlined or other synchronizations
+ * See mem_cgroup_read_stat().
+ */
+ struct mem_cgroup_stat_cpu nocpu_base;
+ spinlock_t pcp_counter_lock;
};
/* Stuffs for move charges at task migration. */
@@ -531,14 +539,40 @@
return mz;
}
+/*
+ * Implementation Note: reading percpu statistics for memcg.
+ *
+ * Both of vmstat[] and percpu_counter has threshold and do periodic
+ * synchronization to implement "quick" read. There are trade-off between
+ * reading cost and precision of value. Then, we may have a chance to implement
+ * a periodic synchronizion of counter in memcg's counter.
+ *
+ * But this _read() function is used for user interface now. The user accounts
+ * memory usage by memory cgroup and he _always_ requires exact value because
+ * he accounts memory. Even if we provide quick-and-fuzzy read, we always
+ * have to visit all online cpus and make sum. So, for now, unnecessary
+ * synchronization is not implemented. (just implemented for cpu hotplug)
+ *
+ * If there are kernel internal actions which can make use of some not-exact
+ * value, and reading all cpu value can be performance bottleneck in some
+ * common workload, threashold and synchonization as vmstat[] should be
+ * implemented.
+ */
static s64 mem_cgroup_read_stat(struct mem_cgroup *mem,
enum mem_cgroup_stat_index idx)
{
int cpu;
s64 val = 0;
- for_each_possible_cpu(cpu)
+ get_online_cpus();
+ for_each_online_cpu(cpu)
val += per_cpu(mem->stat->count[idx], cpu);
+#ifdef CONFIG_HOTPLUG_CPU
+ spin_lock(&mem->pcp_counter_lock);
+ val += mem->nocpu_base.count[idx];
+ spin_unlock(&mem->pcp_counter_lock);
+#endif
+ put_online_cpus();
return val;
}
@@ -663,9 +697,28 @@
/* The caller has to guarantee "mem" exists before calling this */
static struct mem_cgroup *mem_cgroup_start_loop(struct mem_cgroup *mem)
{
- if (mem && css_tryget(&mem->css))
- return mem;
- return NULL;
+ struct cgroup_subsys_state *css;
+ int found;
+
+ if (!mem) /* ROOT cgroup has the smallest ID */
+ return root_mem_cgroup; /*css_put/get against root is ignored*/
+ if (!mem->use_hierarchy) {
+ if (css_tryget(&mem->css))
+ return mem;
+ return NULL;
+ }
+ rcu_read_lock();
+ /*
+ * searching a memory cgroup which has the smallest ID under given
+ * ROOT cgroup. (ID >= 1)
+ */
+ css = css_get_next(&mem_cgroup_subsys, 1, &mem->css, &found);
+ if (css && css_tryget(css))
+ mem = container_of(css, struct mem_cgroup, css);
+ else
+ mem = NULL;
+ rcu_read_unlock();
+ return mem;
}
static struct mem_cgroup *mem_cgroup_get_next(struct mem_cgroup *iter,
@@ -680,9 +733,13 @@
hierarchy_used = iter->use_hierarchy;
css_put(&iter->css);
- if (!cond || !hierarchy_used)
+ /* If no ROOT, walk all, ignore hierarchy */
+ if (!cond || (root && !hierarchy_used))
return NULL;
+ if (!root)
+ root = root_mem_cgroup;
+
do {
iter = NULL;
rcu_read_lock();
@@ -711,6 +768,9 @@
#define for_each_mem_cgroup_tree(iter, root) \
for_each_mem_cgroup_tree_cond(iter, root, true)
+#define for_each_mem_cgroup_all(iter) \
+ for_each_mem_cgroup_tree_cond(iter, NULL, true)
+
static inline bool mem_cgroup_is_root(struct mem_cgroup *mem)
{
@@ -1676,15 +1736,38 @@
atomic_dec(&memcg_drain_count);
}
-static int __cpuinit memcg_stock_cpu_callback(struct notifier_block *nb,
+/*
+ * This function drains percpu counter value from DEAD cpu and
+ * move it to local cpu. Note that this function can be preempted.
+ */
+static void mem_cgroup_drain_pcp_counter(struct mem_cgroup *mem, int cpu)
+{
+ int i;
+
+ spin_lock(&mem->pcp_counter_lock);
+ for (i = 0; i < MEM_CGROUP_STAT_DATA; i++) {
+ s64 x = per_cpu(mem->stat->count[i], cpu);
+
+ per_cpu(mem->stat->count[i], cpu) = 0;
+ mem->nocpu_base.count[i] += x;
+ }
+ spin_unlock(&mem->pcp_counter_lock);
+}
+
+static int __cpuinit memcg_cpu_hotplug_callback(struct notifier_block *nb,
unsigned long action,
void *hcpu)
{
int cpu = (unsigned long)hcpu;
struct memcg_stock_pcp *stock;
+ struct mem_cgroup *iter;
- if (action != CPU_DEAD)
+ if ((action != CPU_DEAD) || action != CPU_DEAD_FROZEN)
return NOTIFY_OK;
+
+ for_each_mem_cgroup_all(iter)
+ mem_cgroup_drain_pcp_counter(iter, cpu);
+
stock = &per_cpu(memcg_stock, cpu);
drain_stock(stock);
return NOTIFY_OK;
@@ -4098,6 +4181,7 @@
vfree(mem);
mem = NULL;
}
+ spin_lock_init(&mem->pcp_counter_lock);
return mem;
}
@@ -4224,7 +4308,7 @@
&per_cpu(memcg_stock, cpu);
INIT_WORK(&stock->work, drain_local_stock);
}
- hotcpu_notifier(memcg_stock_cpu_callback, 0);
+ hotcpu_notifier(memcg_cpu_hotplug_callback, 0);
} else {
parent = mem_cgroup_from_cont(cont->parent);
mem->use_hierarchy = parent->use_hierarchy;