[RFC][mm] [PATCH 1/4] Memory cgroup hierarchy documentation (v2)

[Balbir Singh <balbir@linux.vnet.ibm.com>]

Documentation updates for hierarchy support

Signed-off-by: Balbir Singh <balbir@linux.vnet.ibm.com>
---

 Documentation/controllers/memory.txt |   37 +++++++++++++++++++++++++++++++++++
 1 file changed, 37 insertions(+)

diff -puN Documentation/controllers/memory.txt~memcg-hierarchy-documentation Documentation/controllers/memory.txt
--- linux-2.6.28-rc2/Documentation/controllers/memory.txt~memcg-hierarchy-documentation	2008-11-08 14:09:29.000000000 +0530
+++ linux-2.6.28-rc2-balbir/Documentation/controllers/memory.txt	2008-11-08 14:09:29.000000000 +0530
@@ -245,6 +245,43 @@ cgroup might have some charge associated
 tasks have migrated away from it. Such charges are automatically dropped at
 rmdir() if there are no tasks.
 
+5. Hierarchy support
+
+The memory controller supports a deep hierarchy and hierarchical accounting.
+The hierarchy is created by creating the appropriate cgroups in the
+cgroup filesystem. Consider for example, the following cgroup filesystem
+hierarchy
+
+		root
+	     /  |   \
+           /	|    \
+	  a	b	c
+			| \
+			|  \
+			d   e
+
+In the diagram above, with hierarchical accounting enabled, all memory
+usage of e, is accounted to its ancestors up until the root (i.e, c and root),
+that has memory.use_hierarchy enabled.  If one of the ancestors goes over its
+limit, the reclaim algorithm reclaims from the tasks in the ancestor and the
+children of the ancestor.
+
+5.1 Enabling hierarchical accounting and reclaim
+
+The memory controller by default disables the hierarchy feature. Support
+can be enabled by writing 1 to memory.use_hierarchy file of the root cgroup
+
+# echo 1 > memory.use_hierarchy
+
+The feature can be disabled by
+
+# echo 0 > memory.use_hierarchy
+
+NOTE1: Enabling/disabling will fail if the cgroup already has other
+cgroups created below it.
+
+NOTE2: This feature can be enabled/disabled per subtree.
+
 5. TODO
 
 1. Add support for accounting huge pages (as a separate controller)
_

-- 
	Balbir