linux-kernel - Re: [RFC][PATCH] memcg remove css

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Message-Id: <20100611152144.e53d72b3.kamezawa.hiroyu@jp.fujitsu.com>
Date:	Fri, 11 Jun 2010 15:21:44 +0900
From:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To:	balbir@...ux.vnet.ibm.com
Cc:	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	"nishimura@....nes.nec.co.jp" <nishimura@....nes.nec.co.jp>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [RFC][PATCH] memcg remove css_get/put per pages v2

On Fri, 11 Jun 2010 11:41:02 +0530
Balbir Singh <balbir@...ux.vnet.ibm.com> wrote:

> * KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com> [2010-06-09 15:59:40]:
> 
> > +		if (consume_stock(mem)) {
> > +			/*
> > +			 * It seems dagerous to access memcg without css_get().
> > +			 * But considering how consume_stok works, it's not
> > +			 * necessary. If consume_stock success, some charges
> > +			 * from this memcg are cached on this cpu. So, we
> > +			 * don't need to call css_get()/css_tryget() before
> > +			 * calling consume_stock().
> > +			 */
> > +			rcu_read_unlock();
> > +			goto done;
> > +		}
> > +		if (!css_tryget(&mem->css)) {
> 
> If tryget fails, can one assume that this due to a race and the mem is
> about to be freed?
> 
Yes. it's due to a race and "mem" will be no longer used.
This does the same thing which try_get_mem_cgrou_from_mm() does now.

Thanks,
-Kame

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