[mm] [PATCH 1/4] Memory cgroup hierarchy documentation (v4)

[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 |   38 ++++++++++++++++++++++++++++++++++-
 1 file changed, 37 insertions(+), 1 deletion(-)

diff -puN Documentation/controllers/memory.txt~memcg-hierarchy-documentation Documentation/controllers/memory.txt
--- linux-2.6.28-rc4/Documentation/controllers/memory.txt~memcg-hierarchy-documentation	2008-11-16 13:14:39.000000000 +0530
+++ linux-2.6.28-rc4-balbir/Documentation/controllers/memory.txt	2008-11-16 13:14:39.000000000 +0530
@@ -289,8 +289,44 @@ will be charged as a new owner of it.
   Because rmdir() moves all pages to parent, some out-of-use page caches can be
   moved to the parent. If you want to avoid that, force_empty will be useful.
 
+6. Hierarchy support
 
-6. TODO
+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.
+
+6.1 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.
+
+7. TODO
 
 1. Add support for accounting huge pages (as a separate controller)
 2. Make per-cgroup scanner reclaim not-shared pages first
_

-- 
	Balbir

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