linux-kernel - Re: [PATCH 1/2] memcg: dirty pages accounting and limiting infrastructure

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Message-ID: <20100222180013.GB4052@linux>
Date:	Mon, 22 Feb 2010 19:00:14 +0100
From:	Andrea Righi <arighi@...eler.com>
To:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Cc:	Balbir Singh <balbir@...ux.vnet.ibm.com>,
	Suleiman Souhlal <suleiman@...gle.com>,
	Vivek Goyal <vgoyal@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	containers@...ts.linux-foundation.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] memcg: dirty pages accounting and limiting
 infrastructure

On Mon, Feb 22, 2010 at 09:22:42AM +0900, KAMEZAWA Hiroyuki wrote:

[snip]

> > +static unsigned long get_dirty_bytes(struct mem_cgroup *memcg)
> > +{
> > +	struct cgroup *cgrp = memcg->css.cgroup;
> > +	unsigned long dirty_bytes;
> > +
> > +	/* root ? */
> > +	if (cgrp->parent == NULL)
> > +		return vm_dirty_bytes;
> 
> We have mem_cgroup_is_root() macro.
> 
> > +
> > +	spin_lock(&memcg->reclaim_param_lock);
> > +	dirty_bytes = memcg->dirty_bytes;
> > +	spin_unlock(&memcg->reclaim_param_lock);
> > +
> > +	return dirty_bytes;
> > +}
> Hmm...do we need spinlock ? You use "unsigned long", then, read-write
> is always atomic if not read-modify-write.

I think I simply copy&paste the memcg->swappiness case. But I agree,
read-write should be atomic.

-Andrea
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