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Date: Sat, 21 Jun 2008 18:10:39 +0900
From: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
To: balbir@linux.vnet.ibm.com
Subject: Re: [PATCH] introduce task cgroup v2
Cc: kosaki.motohiro@jp.fujitsu.com, Paul Menage <menage@google.com>,
       Pavel Emelianov <xemul@openvz.org>, containers@lists.osdl.org,
       LKML <linux-kernel@vger.kernel.org>, Li Zefan <lizf@cn.fujitsu.com>,
       Andrew Morton <akpm@linux-foundation.org>
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> > Bad performance on the charge/uncharge?
> > 
> > The only difference I can see is that res_counter uses
> > spin_lock_irqsave()/spin_unlock_irqrestore(), and you're using plain
> > spin_lock()/spin_unlock().
> > 
> > Is the overhead of a pushf/cli/popf really going to matter compared
> > with the overhead of forking/exiting a task?
> > 
> > Or approaching this from the other side, does res_counter really need
> > irq-safe locking, or is it just being cautious?
> 
> We really need irq-safe locking. We can end up uncharging from reclaim context
> (called under zone->lru_lock and mem->zone->lru_lock - held with interrupts
> disabled)
> 
> I am going to convert the spin lock to a reader writers lock, so that reads from
> user space do not cause contention. I'll experiment and look at the overhead.

Sorry, late responce.
I'm working on fix current -mm tree regression recently ;)

Note:

I am going to convert spinlock in task limit cgroup to atomic_t.
task limit cgroup has following caractatics.
	- many write (fork, exit)
	- few read 
	- fork() is performance sensitive systemcall.
	  if increase fork overhead, system total performance cause degression.