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

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Message-ID: <20100222193113.GE3096@redhat.com>
Date:	Mon, 22 Feb 2010 14:31:13 -0500
From:	Vivek Goyal <vgoyal@...hat.com>
To:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Cc:	Andrea Righi <arighi@...eler.com>,
	Balbir Singh <balbir@...ux.vnet.ibm.com>,
	Suleiman Souhlal <suleiman@...gle.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:

[..]
> > +static int mem_cgroup_dirty_bytes_write(struct cgroup *cgrp, struct cftype *cft,
> > +				       u64 val)
> > +{
> > +	struct mem_cgroup *memcg = mem_cgroup_from_cont(cgrp);
> > +	struct mem_cgroup *parent;
> > +
> > +	if (cgrp->parent == NULL)
> > +		return -EINVAL;
> > +
> > +	parent = mem_cgroup_from_cont(cgrp->parent);
> > +
> > +	cgroup_lock();
> > +
> > +	/* If under hierarchy, only empty-root can set this value */
> > +	if ((parent->use_hierarchy) ||
> > +	    (memcg->use_hierarchy && !list_empty(&cgrp->children))) {
> > +		cgroup_unlock();
> > +		return -EINVAL;
> > +	}
> 
> Okay, then, only hierarchy root can set the value.
> Please descirbe this kind of important things in patch description.
> 

Hi Andrea,

Why can only root of the hierarchy set set dirty_bytes value? In this
case, a child cgroup's amount of dirty pages will be controlled by
dirty_ratio?

Thanks
Vivek
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