linux-kernel - Re: [RFC] [PATCH 2/2] cgroups: blkio subsystem as module

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Message-ID: <20100112233453.GB5098@unix37.andrew.cmu.edu>
Date:	Tue, 12 Jan 2010 18:34:53 -0500
From:	Ben Blum <bblum@...rew.cmu.edu>
To:	Vivek Goyal <vgoyal@...hat.com>
Cc:	Li Zefan <lizf@...fujitsu.com>, axboe@...nel.dk,
	ryov@...inux.co.jp,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Andrew Morton <akpm@...ux-foundation.org>, menage@...gle.com,
	containers@...ts.linux-foundation.org,
	linux-kernel@...r.kernel.org, bblum@...rew.cmu.edu
Subject: Re: [RFC] [PATCH 2/2] cgroups: blkio subsystem as module

On Fri, Jan 08, 2010 at 11:33:52AM -0500, Vivek Goyal wrote:
> On Fri, Jan 08, 2010 at 12:30:21AM -0500, Ben Blum wrote:
> > Convert blk-cgroup to be buildable as a module
> > 
> > From: Ben Blum <bblum@...rew.cmu.edu>
> > 
> > This patch modifies the Block I/O cgroup subsystem to be able to be built as a
> > module. As the CFQ disk scheduler optionally depends on blk-cgroup, config
> > options in block/Kconfig, block/Kconfig.iosched, and block/blk-cgroup.h are
> > enhanced to support the new module dependency.
> > 
> > Signed-off-by: Ben Blum <bblum@...rew.cmu.edu>
> 
> Two quick observations with testing.
> 
> You need to EXPORT cgroup_path.
> 
> Second, after loading the module, I mounted the blkio controller. But creating
> a cgroup directory crashed.
> 
> Vivek

argh, good catches on both of them. didn't test with DEBUG_CFQ_IOSCHED
(for cgroup_path) or with making a sub-cgroup (for the crash); shame on
me. turns out it crashed because I had init_idr before init_css_set, and
init_css_set sets css->id = NULL explicitly. fixed patches forthcoming.

-- bblum

---
 block/Kconfig             |    2 -
 block/Kconfig.iosched     |    2 -
 block/blk-cgroup.c        |   53 +++++++++++++++++++++++++++++++++++-----------
 block/blk-cgroup.h        |   10 ++++++--
 include/linux/iocontext.h |    2 -
 kernel/cgroup.c           |   34 ++++++++++++++++++++++++-----
 6 files changed, 80 insertions(+), 23 deletions(-)
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