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Date: Wed, 1 Feb 2012 13:19:05 -0800 From: Tejun Heo <tj@...nel.org> To: axboe@...nel.dk, vgoyal@...hat.com Cc: ctalbott@...gle.com, rni@...gle.com, linux-kernel@...r.kernel.org Subject: [PATCHSET] blkcg: unify blkgs for different policies Hey, again. Currently, blkcg policies have and manage their own blkgs, so blkgs are per cgroup-queue-policy combination instead of cgroup-queue combination. This leads to nasty problems. It isn't clear which part are common to both policies. There are unused duplicates in common part of blkg and it isn't trivial to tell which part is being used. The separation also leads to duplicate logic in both policies which makes the code difficult to follow, prone to subtle bugs and, most importantly, hinders proper layering between blkcg core and policy implementations. Because locking, blkg management, elvswitch and policy [de]registration are tightly woven, it is challenging to untangle - doing proper in-place policy data replacement requires locking improvements which in turn is painful to do when policy implementations are doing their own things with blkgs. As a transitional step, all blkgs other than root one are shot down on policy [de]registration and root blkg is updated in place. This is hackish but should get us through locking update after which we can implement in-place update for all blkgs safely. While this does introduce race window while policies are being [de]registered, this isn't anything new (e.g. none of stat update functions synchronize against policy update) and shouldn't cause any actual problem given blk-throttle can't be built as module and cfq-iosched is default iosched on most installations. This patchset was pretty painful but I think/hope things will be eaiser from here on. Note that this patchset does add ~180 LOC. Some of them are comments and it's expected to shrink again with further cleanups and removal of transitional stuff. Changes to come are: * locking simplification * proper in-place update of policy data for all blkgs on policy change * fix broken blkcg switch after throttling. * use unified stats updated under queue lock and drop percpu stats which should fix locking / context bug across percpu allocation. * make set of applied policies per-queue * move stats and conf into their owning policies and let blkcg core provide generic framework / helper instead of hard coding all the possible ones. This should be accompanied by cgroup updates to allow changing files in cgroupfs. Not sure how this will turn out yet. This patchset contains the following 11 patches. 0001-blkcg-let-blkio_group-point-to-blkio_cgroup-directly.patch 0002-block-relocate-elevator-initialized-test-from-blk_cl.patch 0003-blkcg-add-blkcg_-init-drain-exit-_queue.patch 0004-blkcg-clear-all-request_queues-on-blkcg-policy-un-re.patch 0005-blkcg-let-blkcg-core-handle-policy-private-data-allo.patch 0006-blkcg-move-refcnt-to-blkcg-core.patch 0007-blkcg-make-blkg-pd-an-array-and-move-configuration-a.patch 0008-blkcg-don-t-use-blkg-plid-in-stat-related-functions.patch 0009-blkcg-move-per-queue-blkg-list-heads-and-counters-to.patch 0010-blkcg-let-blkcg-core-manage-per-queue-blkg-list-and-.patch 0011-blkcg-unify-blkg-s-for-blkcg-policies.patch 0001-0003 are prep patches. 0004 shoots down all non-root blkgs on policy [de]registration. 0005 separates per-policy data from common part of blkg and allocate them separately from blkcg core. 0006-0010 collect common data fields and logic from policy implementations into blkcg core. 0011 unifies blkgs so that there's one blkg per cgroup-queue pair. This patchset is on top of v3.3-rc2 62aa2b537c6f5957afd98e29f96897419ed5ebab + [1] blkcg: kill policy node and blkg->dev, take#4 and is also available in the following git branch. git://git.kernel.org/pub/scm/linux/kernel/git/tj/misc.git blkcg-unified-blkg diffstat follows. block/blk-cgroup.c | 674 +++++++++++++++++++++++++++++++++++-------------- block/blk-cgroup.h | 211 +++++++++++---- block/blk-core.c | 26 + block/blk-sysfs.c | 6 block/blk-throttle.c | 232 +++------------- block/blk.h | 2 block/cfq-iosched.c | 274 +++++-------------- block/cfq.h | 96 ++++-- block/elevator.c | 2 include/linux/blkdev.h | 7 10 files changed, 853 insertions(+), 677 deletions(-) Thanks. -- tejun [1] http://thread.gmane.org/gmane.linux.kernel/1247152 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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