memcg: cpu hotplug aware quick acount_move detection

An event counter MEM_CGROUP_ON_MOVE is used for quick check whether file
stat update can be done in async manner or not.  Now, it use percpu
counter and for_each_possible_cpu to update.

This patch replaces for_each_possible_cpu to for_each_online_cpu and adds
necessary synchronization logic at CPU HOTPLUG.

[akpm@linux-foundation.org: coding-style fixes]
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>

1 files changed, 30 insertions, 7 deletions

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 31a1d3b71eee..52840adae62a 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -1132,11 +1132,14 @@ static unsigned int get_swappiness(struct mem_cgroup *memcg)
 static void mem_cgroup_start_move(struct mem_cgroup *mem)
 {
         int cpu;
-        /* Because this is for moving account, reuse mc.lock */
-        spin_lock(&mc.lock);
-        for_each_possible_cpu(cpu)
+
+        get_online_cpus();
+        spin_lock(&mem->pcp_counter_lock);
+        for_each_online_cpu(cpu)
                 per_cpu(mem->stat->count[MEM_CGROUP_ON_MOVE], cpu) += 1;
-        spin_unlock(&mc.lock);
+        mem->nocpu_base.count[MEM_CGROUP_ON_MOVE] += 1;
+        spin_unlock(&mem->pcp_counter_lock);
+        put_online_cpus();
 
         synchronize_rcu();
 }
@@ -1147,10 +1150,13 @@ static void mem_cgroup_end_move(struct mem_cgroup *mem)
 
         if (!mem)
                 return;
-        spin_lock(&mc.lock);
-        for_each_possible_cpu(cpu)
+        get_online_cpus();
+        spin_lock(&mem->pcp_counter_lock);
+        for_each_online_cpu(cpu)
                 per_cpu(mem->stat->count[MEM_CGROUP_ON_MOVE], cpu) -= 1;
-        spin_unlock(&mc.lock);
+        mem->nocpu_base.count[MEM_CGROUP_ON_MOVE] -= 1;
+        spin_unlock(&mem->pcp_counter_lock);
+        put_online_cpus();
 }
 /*
  * 2 routines for checking "mem" is under move_account() or not.
@@ -1751,6 +1757,17 @@ static void mem_cgroup_drain_pcp_counter(struct mem_cgroup *mem, int cpu)
                 per_cpu(mem->stat->count[i], cpu) = 0;
                 mem->nocpu_base.count[i] += x;
         }
+        /* need to clear ON_MOVE value, works as a kind of lock. */
+        per_cpu(mem->stat->count[MEM_CGROUP_ON_MOVE], cpu) = 0;
+        spin_unlock(&mem->pcp_counter_lock);
+}
+
+static void synchronize_mem_cgroup_on_move(struct mem_cgroup *mem, int cpu)
+{
+        int idx = MEM_CGROUP_ON_MOVE;
+
+        spin_lock(&mem->pcp_counter_lock);
+        per_cpu(mem->stat->count[idx], cpu) = mem->nocpu_base.count[idx];
         spin_unlock(&mem->pcp_counter_lock);
 }
 
@@ -1762,6 +1779,12 @@ static int __cpuinit memcg_cpu_hotplug_callback(struct notifier_block *nb,
         struct memcg_stock_pcp *stock;
         struct mem_cgroup *iter;
 
+        if ((action == CPU_ONLINE)) {
+                for_each_mem_cgroup_all(iter)
+                        synchronize_mem_cgroup_on_move(iter, cpu);
+                return NOTIFY_OK;
+        }
+
         if ((action != CPU_DEAD) || action != CPU_DEAD_FROZEN)
                 return NOTIFY_OK;