[RFC] [PATCH 1/5] memcg: simplify account moving check

[KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx>]

>From 528f5f2667da17c26e40d271b24691412e1cbe81 Mon Sep 17 00:00:00 2001
From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx>
Date: Thu, 15 Dec 2011 11:41:18 +0900
Subject: [PATCH 1/5] memcg: simplify account moving check

Now, percpu variable MEM_CGROUP_ON_MOVE is used for indicating that
a memcg is under move_account() and pc->mem_cgroup under it may be
overwritten.

But this value is almost read only and not worth to be percpu.
Using atomic_t instread.

Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx>
---
 mm/memcontrol.c |   44 ++++++++------------------------------------
 1 files changed, 8 insertions(+), 36 deletions(-)

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 996f8f0..d183e1b 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -89,7 +89,6 @@ enum mem_cgroup_stat_index {
 	MEM_CGROUP_STAT_FILE_MAPPED,  /* # of pages charged as file rss */
 	MEM_CGROUP_STAT_SWAPOUT, /* # of pages, swapped out */
 	MEM_CGROUP_STAT_DATA, /* end of data requires synchronization */
-	MEM_CGROUP_ON_MOVE,	/* someone is moving account between groups */
 	MEM_CGROUP_STAT_NSTATS,
 };
 
@@ -289,6 +288,10 @@ struct mem_cgroup {
 	 */
 	int		kmem_independent_accounting;
 	/*
+ 	 * > 0 if a page in this cgroup is under moving account.
+ 	 */
+	atomic_t	moving_account;
+	/*
 	 * percpu counter.
 	 */
 	struct mem_cgroup_stat_cpu *stat;
@@ -1247,32 +1250,15 @@ int mem_cgroup_swappiness(struct mem_cgroup *memcg)
 
 static void mem_cgroup_start_move(struct mem_cgroup *memcg)
 {
-	int cpu;
-
-	get_online_cpus();
-	spin_lock(&memcg->pcp_counter_lock);
-	for_each_online_cpu(cpu)
-		per_cpu(memcg->stat->count[MEM_CGROUP_ON_MOVE], cpu) += 1;
-	memcg->nocpu_base.count[MEM_CGROUP_ON_MOVE] += 1;
-	spin_unlock(&memcg->pcp_counter_lock);
-	put_online_cpus();
-
+	atomic_inc(&memcg->moving_account);
 	synchronize_rcu();
 }
 
 static void mem_cgroup_end_move(struct mem_cgroup *memcg)
 {
-	int cpu;
-
 	if (!memcg)
 		return;
-	get_online_cpus();
-	spin_lock(&memcg->pcp_counter_lock);
-	for_each_online_cpu(cpu)
-		per_cpu(memcg->stat->count[MEM_CGROUP_ON_MOVE], cpu) -= 1;
-	memcg->nocpu_base.count[MEM_CGROUP_ON_MOVE] -= 1;
-	spin_unlock(&memcg->pcp_counter_lock);
-	put_online_cpus();
+	atomic_dec(&memcg->moving_account);
 }
 /*
  * 2 routines for checking "mem" is under move_account() or not.
@@ -1289,7 +1275,7 @@ static void mem_cgroup_end_move(struct mem_cgroup *memcg)
 static bool mem_cgroup_stealed(struct mem_cgroup *memcg)
 {
 	VM_BUG_ON(!rcu_read_lock_held());
-	return this_cpu_read(memcg->stat->count[MEM_CGROUP_ON_MOVE]) > 0;
+	return atomic_read(&memcg->moving_account);
 }
 
 static bool mem_cgroup_under_move(struct mem_cgroup *memcg)
@@ -2058,17 +2044,6 @@ static void mem_cgroup_drain_pcp_counter(struct mem_cgroup *memcg, int cpu)
 		per_cpu(memcg->stat->events[i], cpu) = 0;
 		memcg->nocpu_base.events[i] += x;
 	}
-	/* need to clear ON_MOVE value, works as a kind of lock. */
-	per_cpu(memcg->stat->count[MEM_CGROUP_ON_MOVE], cpu) = 0;
-	spin_unlock(&memcg->pcp_counter_lock);
-}
-
-static void synchronize_mem_cgroup_on_move(struct mem_cgroup *memcg, int cpu)
-{
-	int idx = MEM_CGROUP_ON_MOVE;
-
-	spin_lock(&memcg->pcp_counter_lock);
-	per_cpu(memcg->stat->count[idx], cpu) = memcg->nocpu_base.count[idx];
 	spin_unlock(&memcg->pcp_counter_lock);
 }
 
@@ -2080,11 +2055,8 @@ 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(iter)
-			synchronize_mem_cgroup_on_move(iter, cpu);
+	if ((action == CPU_ONLINE))
 		return NOTIFY_OK;
-	}
 
 	if ((action != CPU_DEAD) || action != CPU_DEAD_FROZEN)
 		return NOTIFY_OK;
-- 
1.7.4.1


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