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

[KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>]

On Mon, 13 Feb 2012 23:21:34 -0800
Greg Thelen <gthelen@google.com> wrote:

> 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
> >
> > A  A  CPU-A A  A  A  A  A  A  A  A  A  A  CPU-B
> > A  A  A  A  A  A  A  A  A  A  A  A  A  A  rcu_read_lock()
> > A  A set flag
> > A  A  A  A  A  A  A  A  A  A  A  A  A  A  if(flag is set)
> > A  A  A  A  A  A  A  A  A  A  A  A  A  A  A  A  A  take heavy lock
> > A  A  A  A  A  A  A  A  A  A  A  A  A  A  do job.
> > A  A synchronize_rcu() A  A  A  A rcu_read_unlock()
> 
> I assume that CPU-A will take heavy lock after synchronize_rcu() when
> updating variables read by CPU-B.
> 
Ah, yes. I should wrote that.

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

Thank you!.

-Kame

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