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

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Date:	Fri, 11 Jun 2010 13:59:41 +0900
From:	Daisuke Nishimura <nishimura@....nes.nec.co.jp>
To:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Cc:	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	"balbir@...ux.vnet.ibm.com" <balbir@...ux.vnet.ibm.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Daisuke Nishimura <nishimura@....nes.nec.co.jp>
Subject: Re: [RFC][PATCH] memcg remove css_get/put per pages v2

On Fri, 11 Jun 2010 13:52:02 +0900, KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com> wrote:
> On Fri, 11 Jun 2010 13:37:44 +0900
> Daisuke Nishimura <nishimura@....nes.nec.co.jp> wrote:
> 
> > > @@ -2432,15 +2463,18 @@ mem_cgroup_uncharge_swapcache(struct pag
> > >  	if (!swapout) /* this was a swap cache but the swap is unused ! */
> > >  		ctype = MEM_CGROUP_CHARGE_TYPE_DROP;
> > >  
> > > -	memcg = __mem_cgroup_uncharge_common(page, ctype);
> > > +	memcg = try_get_mem_cgroup_from_page(page);
> > > +	if (!memcg)
> > > +		return;
> > > +
> > > +	__mem_cgroup_uncharge_common(page, ctype);
> > >  
> > >  	/* record memcg information */
> > > -	if (do_swap_account && swapout && memcg) {
> > > +	if (do_swap_account && swapout) {
> > >  		swap_cgroup_record(ent, css_id(&memcg->css));
> > >  		mem_cgroup_get(memcg);
> > >  	}
> > > -	if (swapout && memcg)
> > > -		css_put(&memcg->css);
> > > +	css_put(&memcg->css);
> > >  }
> > >  #endif
> > >  
> > hmm, this change seems to cause a problem.
> > I can see under flow of mem->memsw and "swap" field in memory.stat. 
> > 
> > I think doing swap_cgroup_record() against mem_cgroup which is not returned
> > by __mem_cgroup_uncharge_common() is a bad behavior.
> > 
> > How about doing like this ? We can safely access mem_cgroup while it has
> > memory.usage, iow, before we call res_counter_uncharge().
> > After this change, it seems to work well.
> > 
> 
> Thank you!. seems to work. I'll merge your change.
> Can I add your Signed-off-by ?
> 
Sure.

Signed-off-by: Daisuke Nishimura <nishimura@....nes.nec.co.jp>
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