[PATCH -V1 9/9] hugetlbfs: Add HugeTLB controller documentation

[Aneesh Kumar K.V]

From: "Aneesh Kumar K.V" <aneesh.kumar@xxxxxxxxxxxxxxxxxx>

Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@xxxxxxxxxxxxxxxxxx>
---
 Documentation/cgroups/hugetlb.txt |   54 +++++++++++++++++++++++++++++++++++++
 1 files changed, 54 insertions(+), 0 deletions(-)
 create mode 100644 Documentation/cgroups/hugetlb.txt

diff --git a/Documentation/cgroups/hugetlb.txt b/Documentation/cgroups/hugetlb.txt
new file mode 100644
index 0000000..722aa8e
--- /dev/null
+++ b/Documentation/cgroups/hugetlb.txt
@@ -0,0 +1,54 @@
+HugeTLB controller
+-----------------
+
+The HugetTLB controller is used to group tasks using cgroups and
+limit the HugeTLB pages used by these groups of tasks. HugetTLB cgroup
+enforce the limit during mmap(2). This enables application to fall back
+to allocation using smaller page size if the cgroup resource limit prevented
+them from allocating HugeTLB pages.
+
+
+The HugetTLB controller supports multi-hierarchy groups and task migration
+across cgroups.
+
+HugeTLB groups can be created by first mounting the cgroup filesystem.
+
+# mount -t cgroup -o hugetlb none /sys/fs/cgroup
+
+With the above step, the initial or the root HugeTLB cgroup becomes
+visible at /sys/fs/cgroup. At bootup, this group includes all the tasks in
+the system. /sys/fs/cgroup/tasks lists the tasks in this cgroup. HugeTLB
+cgroup create seperate limit, usage and max_usage files for each huge page
+size supported. An example listing is given below
+
+hugetlb.16GB.limit_in_bytes
+hugetlb.16GB.max_usage_in_bytes
+hugetlb.16GB.usage_in_bytes
+hugetlb.16MB.limit_in_bytes
+hugetlb.16MB.max_usage_in_bytes
+hugetlb.16MB.usage_in_bytes
+
+/sys/fs/cgroup/hugetlb.<pagesize>.usage_in_bytes  gives the HugeTLB usage
+by this group which is essentially the total size HugeTLB pages obtained
+by all the tasks in the system.
+
+New cgroup can be created under root HugeTLB cgroup /sys/fs/cgroup
+
+# cd /sys/fs/cgroup
+# mkdir g1
+# echo $$ > g1/tasks
+
+The above steps create a new group g1 and move the current shell
+process (bash) into it. 16MB HugeTLB pages consumed by this bash and its
+children can be obtained from g1/hugetlb.16MB.usage_in_bytes and the same
+is accumulated in /sys/fs/cgroup/hugetlb.16MB.usage_in_bytes.
+
+We can limit the usage of 16MB hugepage by a hugeTLB cgroup using
+hugetlb.16MB.limit_in_bytes
+
+# echo 16M > /sys/fs/cgroup/g1/hugetlb.16MB.limit_in_bytes
+# hugectl  --heap=16M /root/heap
+libhugetlbfs: WARNING: New heap segment map at 0x20000000000 failed: Cannot allocate memory
+# echo -1 > /sys/fs/cgroup/g1/hugetlb.16MB.limit_in_bytes
+# hugectl  --heap=16M /root/heap
+#
-- 
1.7.9

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