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-rw-r--r--Documentation/cgroups/blkio-controller.txt29
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
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