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Subject[PATCH v2 3/3][-mm] memcg: cpu hotplug aware quick acount_move detection
From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>

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.

Changelog:
- make use of cpu independent "core" value to synchronize.
- replaces mc.lock with pcp_coutner_lock.

Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
---
mm/memcontrol.c | 37 ++++++++++++++++++++++++++++++-------
1 file changed, 30 insertions(+), 7 deletions(-)

Index: mmotm-0915/mm/memcontrol.c
===================================================================
--- mmotm-0915.orig/mm/memcontrol.c
+++ mmotm-0915/mm/memcontrol.c
@@ -1116,11 +1116,14 @@ static unsigned int get_swappiness(struc
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();
}
@@ -1131,10 +1134,13 @@ static void mem_cgroup_end_move(struct m

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.
@@ -1735,6 +1741,17 @@ static void mem_cgroup_drain_pcp_counter
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);
}

@@ -1746,6 +1763,12 @@ static int __cpuinit memcg_cpu_hotplug_c
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;



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