linux-kernel - Re: [PATCH 15/20] io-controller: map async requests to appropriate cgroup

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Message-Id: <20090528.182740.193697101.ryov@valinux.co.jp>
Date:	Thu, 28 May 2009 18:27:40 +0900 (JST)
From:	Ryo Tsuruta <ryov@...inux.co.jp>
To:	vgoyal@...hat.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,
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	paolo.valente@...more.it, fernando@....ntt.co.jp,
	s-uchida@...jp.nec.com, taka@...inux.co.jp,
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	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 15/20] io-controller: map async requests to appropriate
 cgroup

Hi Vivek,

> +#ifdef CONFIG_TRACK_ASYNC_CONTEXT
> +	if (elv_bio_sync(bio)) {
> +		/* sync io. Determine cgroup from submitting task context. */
> +		cgroup = task_cgroup(current, io_subsys_id);
> +		return cgroup;
> +	}
> +
> +	/* Async io. Determine cgroup from with cgroup id stored in page */
> +	bio_cgroup_id = get_blkio_cgroup_id(bio);
> +
> +	if (!bio_cgroup_id)
> +		return NULL;
> +
> +	cgroup = blkio_cgroup_lookup(bio_cgroup_id);
> +#else
> +	cgroup = task_cgroup(current, io_subsys_id);
> +#endif
> +	return cgroup;
> +}

There is a case where a kernel thread (such as device-mapper drivers)
submits a sync IO instead of a task which originates the IO. I think
you should always use get_blkio_cgroup_id() to determine cgroup.

Thanks,
Ryo Tsuruta
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