linux-kernel - Re: [PATCH] [23/31] HWPOISON: add memory cgroup filter

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Date:	Wed, 9 Dec 2009 14:06:20 +0900
From:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To:	Li Zefan <lizf@...fujitsu.com>
Cc:	Andi Kleen <andi@...stfloor.org>, kosaki.motohiro@...fujitsu.com,
	hugh.dickins@...cali.co.uk, nishimura@....nes.nec.co.jp,
	balbir@...ux.vnet.ibm.com, menage@...gle.com, npiggin@...e.de,
	fengguang.wu@...el.com, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org
Subject: Re: [PATCH] [23/31] HWPOISON: add memory cgroup filter

On Wed, 09 Dec 2009 13:04:06 +0800
Li Zefan <lizf@...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.

Regards,
-Kame

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