[Devel] [PATCH] cgroups: fix set command with beancounters upstream

[Glauber Costa]

The kernel memory controller cannot flip states from unlimited to limited if
there are already tasks in it.  Therefore, we always have to run with *some*
value of kmem enabled. If we don't do it, we can't start unlimited and then use
the set command to set any beancounters. We write the maximum amount minus two
pages, which should effectively mean "accounting turned on, but unlimited"

Signed-off-by: Glauber Costa <glommer at openvz.org>
---
 src/lib/cgroup.c | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/src/lib/cgroup.c b/src/lib/cgroup.c
index 9185d46..ae7fe5c 100644
--- a/src/lib/cgroup.c
+++ b/src/lib/cgroup.c
@@ -56,6 +56,19 @@ static int controller_apply_config(struct cgroup *ct, struct cgroup *parent,
 	} else if (!strcmp("memory", name)) {
 		if ((ret = cgroup_set_value_string(controller, "memory.use_hierarchy", "1")))
 			return ret;
+		/*
+		 * The kernel memory controller cannot flip states from
+		 * unlimited to limited if there are already tasks in it.
+		 * Therefore, we always have to run with *some* value of kmem
+		 * enabled. If we don't do it, we can't start unlimited and
+		 * then use the set command to set any beancounters. We write
+		 * The maximum amount minus two pages, which should effectively
+		 * mean "accounting turned on, but unlimited". This will fail
+		 * if the kmem controller is not present, but that is okay.
+		 */
+		cgroup_set_value_string(controller, "memory.kmem.limit_in_bytes",
+					"9223372036854767712");
+
 	} else if (!strcmp("devices", name)) {
 		if ((ret = cgroup_set_value_string(controller, "devices.deny", "a")))
 			return ret;
-- 
1.7.11.7