Date: Wed, 9 Dec 2009 11:03:33 +0530
From: Balbir Singh <balbir@linux.vnet.ibm.com>
To: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Li Zefan <lizf@cn.fujitsu.com>, Andi Kleen <andi@firstfloor.org>,
       kosaki.motohiro@jp.fujitsu.com, hugh.dickins@tiscali.co.uk,
       nishimura@mxp.nes.nec.co.jp, menage@google.com, npiggin@suse.de,
       fengguang.wu@intel.com, linux-kernel@vger.kernel.org,
       linux-mm@kvack.org
Subject: Re: [PATCH] [23/31] HWPOISON: add memory cgroup filter
Message-ID: <20091209053333.GC3722@balbir.in.ibm.com>
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* KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> [2009-12-09 14:06:20]:

> On Wed, 09 Dec 2009 13:04:06 +0800
> Li Zefan <lizf@cn.fujitsu.com> wrote:
> 
> > > +#ifdef	CONFIG_CGROUP_MEM_RES_CTLR_SWAP
> > > +u64 hwpoison_filter_memcg;
> > > +EXPORT_SYMBOL_GPL(hwpoison_filter_memcg);
> > > +static int hwpoison_filter_task(struct page *p)
> > > +{
> > > +	struct mem_cgroup *mem;
> > > +	struct cgroup_subsys_state *css;
> > > +	unsigned long ino;
> > > +
> > > +	if (!hwpoison_filter_memcg)
> > > +		return 0;
> > > +
> > > +	mem = try_get_mem_cgroup_from_page(p);
> > > +	if (!mem)
> > > +		return -EINVAL;
> > > +
> > > +	css = mem_cgroup_css(mem);
> > > +	ino = css->cgroup->dentry->d_inode->i_ino;
> > 
> > I have a question, can try_get_mem_cgroup_from_page() return
> > root_mem_cgroup?
> > 
> yes.
> 
> > if it can, then css->cgroup->dentry is NULL, if memcg is
> > not mounted and there is no subdir in memcg. Because the root
> > cgroup of an inactive subsystem has no dentry.
> > 
> 
> Nice catch. It sounds possible. That should be handled.
> 
> 

Yes, agreed, good catch!

-- 
	Balbir
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