blk-throttle: implement proper hierarchy support

With the recent updates, blk-throttle is finally ready for proper
hierarchy support.  Dispatching now honors service_queue->parent_sq
and propagates correctly.  The only thing missing is setting
->parent_sq correctly so that throtl_grp hierarchy matches the cgroup
hierarchy.

This patch updates throtl_pd_init() such that service_queues form the
same hierarchy as the cgroup hierarchy if sane_behavior is enabled.
As this concludes proper hierarchy support for blkcg, the shameful
.broken_hierarchy tag is removed from blkio_subsys.

v2: Updated blkio-controller.txt as suggested by Vivek.

Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: Vivek Goyal <vgoyal@redhat.com>
Cc: Li Zefan <lizefan@huawei.com>

1 files changed, 15 insertions, 14 deletions

diff --git a/Documentation/cgroups/blkio-controller.txt b/Documentation/cgroups/blkio-controller.txt
index da272c8f44e7..cd556b914786 100644
--- a/Documentation/cgroups/blkio-controller.txt
+++ b/Documentation/cgroups/blkio-controller.txt
@@ -94,11 +94,13 @@ Throttling/Upper Limit policy
 
 Hierarchical Cgroups
 ====================
-- Currently only CFQ supports hierarchical groups. For throttling,
-  cgroup interface does allow creation of hierarchical cgroups and
-  internally it treats them as flat hierarchy.
 
-  If somebody created a hierarchy like as follows.
+Both CFQ and throttling implement hierarchy support; however,
+throttling's hierarchy support is enabled iff "sane_behavior" is
+enabled from cgroup side, which currently is a development option and
+not publicly available.
+
+If somebody created a hierarchy like as follows.
 
                         root
                         /  \
@@ -106,21 +108,20 @@ Hierarchical Cgroups
                         |
                      test3
 
-  CFQ will handle the hierarchy correctly but and throttling will
-  practically treat all groups at same level. For details on CFQ
-  hierarchy support, refer to Documentation/block/cfq-iosched.txt.
-  Throttling will treat the hierarchy as if it looks like the
-  following.
+CFQ by default and throttling with "sane_behavior" will handle the
+hierarchy correctly.  For details on CFQ hierarchy support, refer to
+Documentation/block/cfq-iosched.txt.  For throttling, all limits apply
+to the whole subtree while all statistics are local to the IOs
+directly generated by tasks in that cgroup.
+
+Throttling without "sane_behavior" enabled from cgroup side will
+practically treat all groups at same level as if it looks like the
+following.
 
                                 pivot
                              /  /   \  \
                         root  test1 test2  test3
 
-  Nesting cgroups, while allowed, isn't officially supported and blkio
-  genereates warning when cgroups nest. Once throttling implements
-  hierarchy support, hierarchy will be supported and the warning will
-  be removed.
-
 Various user visible config options
 ===================================
 CONFIG_BLK_CGROUP