linux-kernel - Re: [PATCH 09/25] io-controller: Common hierarchical fair queuing code in elevaotor layer

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Date:	Mon, 6 Jul 2009 10:16:50 -0400
From:	Vivek Goyal <vgoyal@...hat.com>
To:	Gui Jianfeng <guijianfeng@...fujitsu.com>
Cc:	linux-kernel@...r.kernel.org,
	containers@...ts.linux-foundation.org, dm-devel@...hat.com,
	jens.axboe@...cle.com, nauman@...gle.com, dpshah@...gle.com,
	lizf@...fujitsu.com, mikew@...gle.com, fchecconi@...il.com,
	paolo.valente@...more.it, ryov@...inux.co.jp,
	fernando@....ntt.co.jp, s-uchida@...jp.nec.com, taka@...inux.co.jp,
	jmoyer@...hat.com, dhaval@...ux.vnet.ibm.com,
	balbir@...ux.vnet.ibm.com, righi.andrea@...il.com,
	m-ikeda@...jp.nec.com, jbaron@...hat.com, agk@...hat.com,
	snitzer@...hat.com, akpm@...ux-foundation.org, peterz@...radead.org
Subject: Re: [PATCH 09/25] io-controller: Common hierarchical fair queuing
	code in elevaotor layer

On Mon, Jul 06, 2009 at 10:46:19AM +0800, Gui Jianfeng wrote:
> Vivek Goyal wrote:
> ...
> > +static struct io_group *
> > +io_group_chain_alloc(struct request_queue *q, void *key, struct cgroup *cgroup)
> > +{
> > +	struct io_cgroup *iocg;
> > +	struct io_group *iog, *leaf = NULL, *prev = NULL;
> > +	gfp_t flags = GFP_ATOMIC |  __GFP_ZERO;
> > +
> > +	for (; cgroup != NULL; cgroup = cgroup->parent) {
> > +		iocg = cgroup_to_io_cgroup(cgroup);
> > +
> > +		iog = io_cgroup_lookup_group(iocg, key);
> > +		if (iog != NULL) {
> > +			/*
> > +			 * All the cgroups in the path from there to the
> > +			 * root must have a io_group for efqd, so we don't
> > +			 * need any more allocations.
> > +			 */
> > +			break;
> > +		}
> > +
> > +		iog = kzalloc_node(sizeof(*iog), flags, q->node);
> > +		if (!iog)
> > +			goto cleanup;
> > +
> > +		iog->iocg_id = css_id(&iocg->css);
> 
>   Hi Vivek,
> 
>   IMHO, The io_cgroup id is nothing more than keeping track the corresponding iocg.
>   So why not just store iocg pointer in io_group and just get rid of this complexity.
>   I'd like to post a patch to do this change, what's your opinion?
> 

Hi Gui,

You can try that but I suspect that there not much to be gained in
terms of number of lines of code or code complexity. Do try it out though
and we can then have a look at the patch.

Thanks
Vivek
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