linux-kernel - Re: [PATCH 3/3] cgroup: remove extra calls to find_existing_css

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Message-ID: <20120105173530.GB18486@google.com>
Date:	Thu, 5 Jan 2012 09:35:30 -0800
From:	Tejun Heo <tj@...nel.org>
To:	Li Zefan <lizf@...fujitsu.com>
Cc:	Mandeep Singh Baines <msb@...omium.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	linux-kernel@...r.kernel.org,
	containers@...ts.linux-foundation.org, cgroups@...r.kernel.org,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Oleg Nesterov <oleg@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Paul Menage <paul@...lmenage.org>
Subject: Re: [PATCH 3/3] cgroup: remove extra calls to find_existing_css_set

Hello, guys.

On Thu, Jan 05, 2012 at 10:10:57AM +0800, Li Zefan wrote:
> Mandeep Singh Baines wrote:
> > In cgroup_attach_proc, we indirectly call find_existing_css_set 3
> > times. It is an expensive call so we want to call it a minimum
> > of times. This patch only calls it once and stores the result so
> > that it can be used later on when we call cgroup_task_migrate.
> > 
> > This required modifying cgroup_task_migrate to take the new css_set
> > (which we obtained from find_css_set) as a parameter. The nice side
> > effect of this is that cgroup_task_migrate is now identical for
> > cgroup_attach_task and cgroup_attach_proc. It also now returns a
> > void since it can never fail.
> > 
> > Changes in V4:
> > * https://lkml.org/lkml/2011/12/22/421 (Li Zefan)
> >   * Avoid GFP_KERNEL (sleep) in rcu_read_lock by getting css_set in
> >     a separate loop not under an rcu_read_lock
> > Changes in V3:
> > * https://lkml.org/lkml/2011/12/22/13 (Li Zefan)
> >   * Fixed earlier bug by creating a seperate patch to remove tasklist_lock
> > Changes in V2:
> > * https://lkml.org/lkml/2011/12/20/372 (Tejun Heo)
> >   * Move find_css_set call into loop which creates the flex array
> > * Author
> >   * Kill css_set_refs and use group_size instead
> >   * Fix an off-by-one error in counting css_set refs
> >   * Add a retval check in out_list_teardown
> > 
> > Signed-off-by: Mandeep Singh Baines <msb@...omium.org>
> 
> Acked-by: Li Zefan <lizf@...fujitsu.com>

I like this series but it's too late for the current merge window.
I'll apply them on for-3.4 once this merge window closes.  If I don't,
please ping me.

Thank you.

-- 
tejun
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