From: Vivek Goyal <vgoyal@redhat.com>
To: Tejun Heo <tj@kernel.org>
Cc: axboe@kernel.dk, ctalbott@google.com, rni@google.com,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH 12/12] blkcg: kill the mind-bending blkg->dev
Date: Thu, 19 Jan 2012 10:49:19 -0500 [thread overview]
Message-ID: <20120119154919.GA10908@redhat.com> (raw)
In-Reply-To: <1326935490-11827-13-git-send-email-tj@kernel.org>
On Wed, Jan 18, 2012 at 05:11:30PM -0800, Tejun Heo wrote:
> blkg->dev is dev_t recording the device number of the block device for
> the associated request_queue. It is used to identify the associated
> block device when printing out configuration or stats.
>
> This is redundant to begin with. A blkg is an association between a
> cgroup and a request_queue and it of course is possible to reach
> request_queue from blkg and synchronization conventions are in place
> for safe q dereferencing, so this shouldn't be necessary from the
> beginning. Furthermore, it's initialized by sscanf()ing the device
> name of backing_dev_info. The mind boggles.
>
> Anyways, if blkg is visible under rcu lock, we *know* that the
> associated request_queue hasn't gone away yet and its bdi is
> registered and alive - blkg can't be created for request_queue which
> hasn't been fully initialized and it can't go away before blkg is
> removed.
>
> Let stat and conf read functions get device name from
> blkg->q->backing_dev_info.dev and pass it down to printing functions
> and remove blkg->dev.
I think one of the reasons for not using blkg->q->backing_dev_info.dev was
that there were still drivers where multiple gendisks were sharing the
request queue.
Thanks
Vivek
next prev parent reply other threads:[~2012-01-19 15:49 UTC|newest]
Thread overview: 36+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-01-19 1:11 [PATCHSET] blkcg: kill policy node and blkg->dev Tejun Heo
2012-01-19 1:11 ` [PATCH 01/12] blkcg: obtaining blkg should be enclosed inside rcu_read_lock() Tejun Heo
2012-01-19 10:07 ` Vivek Goyal
2012-01-19 15:39 ` Tejun Heo
2012-01-19 15:54 ` Vivek Goyal
2012-01-19 15:58 ` Tejun Heo
2012-01-19 1:11 ` [PATCH 02/12] cfq: don't register propio policy if !CONFIG_CFQ_GROUP_IOSCHED Tejun Heo
2012-01-19 10:11 ` Vivek Goyal
2012-01-19 1:11 ` [PATCH 03/12] elevator: clear auxiliary data earlier during elevator switch Tejun Heo
2012-01-19 1:11 ` [PATCH 04/12] elevator: make elevator_init_fn() return 0/-errno Tejun Heo
2012-01-19 11:11 ` Vivek Goyal
2012-01-19 15:44 ` Tejun Heo
2012-01-19 1:11 ` [PATCH 05/12] blkcg: update blkg get functions take blkio_cgroup as parameter Tejun Heo
2012-01-19 11:21 ` Vivek Goyal
2012-01-19 15:45 ` Tejun Heo
2012-01-19 1:11 ` [PATCH 06/12] blkcg: use q and plid instead of opaque void * for blkio_group association Tejun Heo
2012-01-19 14:04 ` Vivek Goyal
2012-01-19 15:55 ` Tejun Heo
2012-01-19 16:16 ` Vivek Goyal
2012-01-19 16:25 ` Tejun Heo
2012-01-19 16:42 ` Tejun Heo
2012-01-19 1:11 ` [PATCH 07/12] blkcg: add blkio_policy[] array and allow one policy per policy ID Tejun Heo
2012-01-19 1:11 ` [PATCH 08/12] blkcg: use the usual get blkg path for root blkio_group Tejun Heo
2012-01-19 14:41 ` Vivek Goyal
2012-01-19 16:17 ` Tejun Heo
2012-01-19 1:11 ` [PATCH 09/12] blkcg: factor out blkio_group creation Tejun Heo
2012-01-19 1:11 ` [PATCH 10/12] blkcg: don't allow or retain configuration of missing devices Tejun Heo
2012-01-19 1:11 ` [PATCH 11/12] blkcg: kill blkio_policy_node Tejun Heo
2012-01-19 20:32 ` Vivek Goyal
2012-01-19 22:03 ` Tejun Heo
2012-01-19 22:30 ` Vivek Goyal
2012-01-19 1:11 ` [PATCH 12/12] blkcg: kill the mind-bending blkg->dev Tejun Heo
2012-01-19 15:49 ` Vivek Goyal [this message]
2012-01-19 16:30 ` Tejun Heo
2012-01-19 16:46 ` Vivek Goyal
2012-01-19 1:18 ` [PATCHSET] blkcg: kill policy node and blkg->dev Tejun Heo
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