linux-kernel - Re: [PATCH 1/9] io-throttle documentation

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Message-Id: <20090427.211533.115916003.ryov@valinux.co.jp>
Date:	Mon, 27 Apr 2009 21:15:33 +0900 (JST)
From:	Ryo Tsuruta <ryov@...inux.co.jp>
To:	righi.andrea@...il.com
Cc:	randy.dunlap@...cle.com, menage@...gle.com, chlunde@...g.uio.no,
	eric.rannaud@...il.com, balbir@...ux.vnet.ibm.com,
	fernando@....ntt.co.jp, dradford@...ehost.com, agk@...rceware.org,
	subrata@...ux.vnet.ibm.com, axboe@...nel.dk,
	akpm@...ux-foundation.org, containers@...ts.linux-foundation.org,
	linux-kernel@...r.kernel.org, dave@...ux.vnet.ibm.com,
	matt@...ehost.com, roberto@...it.it, ngupta@...gle.com
Subject: Re: [PATCH 1/9] io-throttle documentation

Hi Kamezawa-san,

> I've come up with an idea to coexist blkio-cgroup and io-throttle.
> blkio-cgroup provides a function to get a cgroup with the specified ID.
> 
> /* Should be called under rcu_read_lock() */
> struct cgroup *blkio_cgroup_lookup(int id)
> {
> 	struct cgroup *cgrp;
> 	struct cgroup_subsys_state *css;
> 	
> 	if (blkio_cgroup_disabled())
> 		return NULL;
> 
> 	css = css_lookup(&blkio_cgroup_subsys, id);
> 	if (!css)
> 		return NULL;
> 	cgrp = css->cgroup;
> 	return cgrp;
> }
> 
> Then io-throttle can get a struct iothrottle which belongs to the
> cgroup by using the above function.
> 
> static struct iothrottle *iothrottle_lookup(int id)
> {
> 	struct cgroup *grp;
> 	struct iothrottle *iot;
> 
> 	...
> 	grp = blkio_cgroup_lookup(id);
> 	if (!grp)
> 		return NULL
> 	iot = cgroup_to_iothrottle(grp);
> 	...
> }
> 
> What do you think about this way?

I have some questions. 
- How about using the same numbering scheme as process ID for css_id
  instead of idr? It prevents the same ID from being resued quickly.
- Why are css_ids assigned per css? If each cgroup has a unique ID and
  the subsystems can refer to it, I can make the above code simple.

Thanks,
Ryo Tsuruta
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