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Date: Tue, 21 Sep 2010 18:35:27 +0900
From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Cc: "linux-mm@...ck.org" <linux-mm@...ck.org>,
"balbir@...ux.vnet.ibm.com" <balbir@...ux.vnet.ibm.com>,
"nishimura@....nes.nec.co.jp" <nishimura@....nes.nec.co.jp>,
"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: [PATCH v2 2/3][-mm] memcg: cpu hotplug aware percpu count updates
From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
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.
Changelog: 2010/09/21
- add and use for_each_mem_cgroup_all()
- added "core" value and spin_lock.
- added Implementation Note for future updates.
- divided out "MEM_CGROUP_ON_MOVE" handling.
Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
---
mm/memcontrol.c | 80 +++++++++++++++++++++++++++++++++++++++++++++++++++-----
1 file changed, 74 insertions(+), 6 deletions(-)
Index: mmotm-0915/mm/memcontrol.c
===================================================================
--- mmotm-0915.orig/mm/memcontrol.c
+++ mmotm-0915/mm/memcontrol.c
@@ -89,7 +89,9 @@ enum mem_cgroup_stat_index {
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 @@ struct mem_cgroup {
* 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 @@ mem_cgroup_largest_soft_limit_node(struc
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;
}
@@ -665,6 +699,9 @@ static struct mem_cgroup *mem_cgroup_sta
{
if (mem && css_tryget(&mem->css))
return mem;
+ if (!mem)
+ return root_mem_cgroup; /*css_put/get against root is ignored*/
+
return NULL;
}
@@ -680,9 +717,13 @@ static struct mem_cgroup *mem_cgroup_get
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 +752,9 @@ static struct mem_cgroup *mem_cgroup_get
#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 +1720,38 @@ static void drain_all_stock_sync(void)
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;
@@ -4094,6 +4161,7 @@ static struct mem_cgroup *mem_cgroup_all
vfree(mem);
mem = NULL;
}
+ spin_lock_init(&mem->pcp_counter_lock);
return mem;
}
@@ -4220,7 +4288,7 @@ mem_cgroup_create(struct cgroup_subsys *
&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;
--
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