From d1942f3fe2ad08225048a22da2029cc88941eab2 Mon Sep 17 00:00:00 2001
From: Balbir Singh <balbir@linux.vnet.ibm.com>
Date: Wed, 7 Jan 2009 18:08:03 -0800
Subject: [PATCH] --- yaml --- r: 127568 b: refs/heads/master c:
 52bc0d82100cd896213a9a25ec01c1ba87b939db h: refs/heads/master v: v3

---
 [refs]                                     |  2 +-
 trunk/Documentation/controllers/memory.txt | 38 +++++++++++++++++++++-
 2 files changed, 38 insertions(+), 2 deletions(-)

diff --git a/[refs] b/[refs]
index 9f3268b3e304..24818294f1ad 100644
--- a/[refs]
+++ b/[refs]
@@ -1,2 +1,2 @@
 ---
-refs/heads/master: f8d665422603ee1b8ed04dcad4242f14d623c941
+refs/heads/master: 52bc0d82100cd896213a9a25ec01c1ba87b939db
diff --git a/trunk/Documentation/controllers/memory.txt b/trunk/Documentation/controllers/memory.txt
index 05fe29ab1e58..09e1c737d285 100644
--- a/trunk/Documentation/controllers/memory.txt
+++ b/trunk/Documentation/controllers/memory.txt
@@ -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