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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
94 94
95Hierarchical Cgroups 95Hierarchical Cgroups
96==================== 96====================
97- Currently only CFQ supports hierarchical groups. For throttling,
98 cgroup interface does allow creation of hierarchical cgroups and
99 internally it treats them as flat hierarchy.
100 97
101 If somebody created a hierarchy like as follows. 98Both CFQ and throttling implement hierarchy support; however,
99throttling's hierarchy support is enabled iff "sane_behavior" is
100enabled from cgroup side, which currently is a development option and
101not publicly available.
102
103If somebody created a hierarchy like as follows.
102 104
103 root 105 root
104 / \ 106 / \
@@ -106,21 +108,20 @@ Hierarchical Cgroups
106 | 108 |
107 test3 109 test3
108 110
109 CFQ will handle the hierarchy correctly but and throttling will 111CFQ by default and throttling with "sane_behavior" will handle the
110 practically treat all groups at same level. For details on CFQ 112hierarchy correctly. For details on CFQ hierarchy support, refer to
111 hierarchy support, refer to Documentation/block/cfq-iosched.txt. 113Documentation/block/cfq-iosched.txt. For throttling, all limits apply
112 Throttling will treat the hierarchy as if it looks like the 114to the whole subtree while all statistics are local to the IOs
113 following. 115directly generated by tasks in that cgroup.
116
117Throttling without "sane_behavior" enabled from cgroup side will
118practically treat all groups at same level as if it looks like the
119following.
114 120
115 pivot 121 pivot
116 / / \ \ 122 / / \ \
117 root test1 test2 test3 123 root test1 test2 test3
118 124
119 Nesting cgroups, while allowed, isn't officially supported and blkio
120 genereates warning when cgroups nest. Once throttling implements
121 hierarchy support, hierarchy will be supported and the warning will
122 be removed.
123
124Various user visible config options 125Various user visible config options
125=================================== 126===================================
126CONFIG_BLK_CGROUP 127CONFIG_BLK_CGROUP