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Subject[PATCHSET] blkcg: update locking and fix stacking
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Hey, guys.

This is the third patchset of blkcg API cleanup series and does the
following two things.

* Drops RCU and use double locking. As with ioc, we might want to
re-introduce RCU in more restricted form to walk blkg from blkcg but
for now there's no need. cgroup deletion is much colder than task
exit and there's no other path which requires reverse double
locking.

* Before this patchset, blk-throttle and cfq-iosched propio couldn't
be used together because for any bios delayed by blk-throttle would
be issued by a worker thread and get dumped to the default cgroup.
So, bios will be nondeterministically thrown into the root cg. This
isn't a problem limited to blk-throttle. Any mechanism which punts
bios to a different task (e.g. btrfs) would mess up IO scheduling
for both cgroups and iocontexts.

This patchset implements a mechanism to associate a bio to a task
(its cgroup and ioc actually) and block layer will handle the
request as if it were issued by the associated task no matter which
task actually ends up issuing it to block layer. It's applied to
blk-throttle such that any delayed bio is associated to the original
task.

This patchset contains the following 9 patches.

0001-blkcg-use-double-locking-instead-of-RCU-for-blkg-syn.patch
0002-blkcg-drop-unnecessary-RCU-locking.patch
0003-block-restructure-get_request.patch
0004-block-interface-update-for-ioc-icq-creation-function.patch
0005-block-ioc_task_link-can-t-fail.patch
0006-block-add-io_context-active_ref.patch
0007-block-implement-bio_associate_current.patch
0008-block-make-block-cgroup-policies-follow-bio-task-ass.patch
0009-block-make-blk-throttle-preserve-the-issuing-task-on.patch

0001-0002 updates locking and strips out RCU.

0003-0006 prepare for bio task association.

0007-0009 implement bio task association and apply it to
blk-throttle.

This patchset is on top of

block/for-linus 621032ad6eaabf2fe771c4fa0d8f58e1fcfcdba6
+ [1] blkcg: kill policy node and blkg->dev, take#4
+ [2] blkcg: unify blkgs for different policies (updated)

and is also available in the following git branch.

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

The git branch has separate branches for previous patchsets, so using
it probably is the easiest way to review this series. Jens, if you
want the whole thing reposted, please let me know.

diffstat follows.

block/blk-cgroup.c | 167 +++++++++++++++++-----------------------------
block/blk-cgroup.h | 12 +--
block/blk-core.c | 92 ++++++++++++++-----------
block/blk-ioc.c | 58 +++++++++------
block/blk-throttle.c | 41 +----------
block/blk.h | 24 +++---
block/cfq-iosched.c | 54 ++++----------
block/cfq.h | 10 --
block/elevator.c | 5 -
fs/bio.c | 61 ++++++++++++++++
include/linux/bio.h | 8 ++
include/linux/blk_types.h | 10 ++
include/linux/blkdev.h | 1
include/linux/elevator.h | 6 +
include/linux/iocontext.h | 32 ++++++--
kernel/fork.c | 5 -
16 files changed, 299 insertions(+), 287 deletions(-)

Thanks.

--
tejun

[1] http://thread.gmane.org/gmane.linux.kernel/1247152
[2] http://thread.gmane.org/gmane.linux.kernel/1247287


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