Re: [PATCH 2/6 v4] memcg: simplify move_account() check

[Greg Thelen <gthelen@google.com>]

On Mon, Feb 13, 2012 at 7:07 PM, KAMEZAWA Hiroyuki
<kamezawa.hiroyu@jp.fujitsu.com> wrote:
> From 9cdb3b63dc8d08cc2220c54c80438c13433a0d12 Mon Sep 17 00:00:00 2001
> From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
> Date: Thu, 2 Feb 2012 10:02:39 +0900
> Subject: [PATCH 2/6] memcg: simplify move_account() check.
>
> In memcg, for avoiding take-lock-irq-off at accessing page_cgroup,
> a logic, flag + rcu_read_lock(), is used. This works as following
>
>     CPU-A                     CPU-B
>                             rcu_read_lock()
>    set flag
>                             if(flag is set)
>                                   take heavy lock
>                             do job.
>    synchronize_rcu()        rcu_read_unlock()

I assume that CPU-A will take heavy lock after synchronize_rcu() when
updating variables read by CPU-B.

>  memcontrol.c |   65 ++++++++++++++++++++++-------------------------------------
>  1 file changed, 25 insertions(+), 40 deletions(-)
>
> Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>

Acked-by: Greg Thelen <gthelen@google.com>

> ---
>  mm/memcontrol.c |   70 +++++++++++++++++++++++-------------------------------
>  1 files changed, 30 insertions(+), 40 deletions(-)

> @@ -2089,11 +2082,8 @@ 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))

Extra parenthesis.  I recommend:
+       if (action == CPU_ONLINE)

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