[PATCHSET] blkcg: kill policy node and blkg->dev, take#4

[Tejun Heo]

Hello, guys.

This is the fourth take of blkcg-kill-policy-node-and-blkg_dev
patchset.  Changes from the last take[L] are,

* blkcg_clear_queue() renamed to blkg_destroy_all() and relocated for
  consistency with later changes.

* blk_lookup_create() updated to take @for_root to allow root blkg
  creation during elevator switch while the queue is being bypassed.
  The function is also updated to return ERR_PTR() value so that the
  caller can distinguish transitional failure due to queue bypass.

* blkg root group creation now uses blkg_lookup_create() directly for
  both blk-throttle and cfq-iosched.  This allows making both policy
  specific blkg lookup_create functions behave similarly.

* cfq_clear_queue() checks q->elevator before dereferencing it to
  determine elevator type.  This avoids NULL dereference during policy
  [un]registration.

blk-cgroup, blk-throttle and cfq-iosched are pretty tightly tangled
and untangling requires seemingly unrelated changes and addition of
some transitional stuff.  Some are in this patchset but they'll be
more prominent in the second patchset.  This patchset concentrates on
removing blkio_policy_node and blkio_group->dev, and preparing for the
next patchset which will unify blkg so that there's single blkg per
cgroup - request_queue pair.

blkio_policy_node carries configuration per cgroup-request_queue
association separately from the matching blkio_group.  The goal seems
to be allowing configuration of missing devices and retaining
configuration across hot unplug/plug cycles.  Such behavior is very
different from existing conventions, misleading and unnecessary.  This
patchset moves configuration to blkio_group and removes
blkio_policy_node.

blkg->dev removal is much simpler.  blkg->dev is used to print out
device number when printing out per-device configurations or
statistics.  The device name can be easily determined by following the
associated request_queue from blkg instead.

This patchset makes the following two userland visible behavior
changes.

* Per-device blkcg configuration can't be done for non-existing
  devices.  This behavior change is intentional and permanent.

* Switching elevator clears per-device blk-throtl configuration.  This
  behavior change is transitional and will be restored with later
  patches.

This patchset contains the following 16 patches.

0001-blkcg-make-CONFIG_BLK_CGROUP-bool.patch
0002-cfq-don-t-register-propio-policy-if-CONFIG_CFQ_GROUP.patch
0003-elevator-clear-auxiliary-data-earlier-during-elevato.patch
0004-elevator-make-elevator_init_fn-return-0-errno.patch
0005-block-implement-blk_queue_bypass_start-end.patch
0006-block-extend-queue-bypassing-to-cover-blkcg-policies.patch
0007-blkcg-shoot-down-blkio_groups-on-elevator-switch.patch
0008-blkcg-move-rcu_read_lock-outside-of-blkio_group-get-.patch
0009-blkcg-update-blkg-get-functions-take-blkio_cgroup-as.patch
0010-blkcg-use-q-and-plid-instead-of-opaque-void-for-blki.patch
0011-blkcg-add-blkio_policy-array-and-allow-one-policy-pe.patch
0012-blkcg-use-the-usual-get-blkg-path-for-root-blkio_gro.patch
0013-blkcg-factor-out-blkio_group-creation.patch
0014-blkcg-don-t-allow-or-retain-configuration-of-missing.patch
0015-blkcg-kill-blkio_policy_node.patch
0016-blkcg-kill-the-mind-bending-blkg-dev.patch

0001-0004: misc preps including elevator switch update

0005-0007: ensure blkcg policies are quiescent across elvswitch

0008-0013: move common part of blkg management into blkcg core

0014-0015: kill blkio_policy_node

0016     : kill blkg->dev

This patchset is on top of v3.3-rc2 and also available in the
following git branch.

  git://git.kernel.org/pub/scm/linux/kernel/git/tj/misc.git blkcg-kill-pn

 block/Kconfig.iosched    |    4 
 block/blk-cgroup.c       |  701 +++++++++++++++++------------------------------
 block/blk-cgroup.h       |  106 ++-----
 block/blk-core.c         |   53 +++
 block/blk-throttle.c     |  297 +++++++------------
 block/blk.h              |    6 
 block/cfq-iosched.c      |  296 ++++++++-----------
 block/cfq.h              |    7 
 block/deadline-iosched.c |    8 
 block/elevator.c         |  116 +++----
 block/noop-iosched.c     |    8 
 include/linux/blkdev.h   |    5 
 include/linux/elevator.h |    2 
 init/Kconfig             |    2 
 14 files changed, 639 insertions(+), 972 deletions(-)

Thanks.

--
tejun

[L] http://thread.gmane.org/gmane.linux.kernel/1242764
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