[Lxc-users] total RAM limit

[Serge Hallyn]

Quoting Gary Ballantyne (gary.ballantyne at haulashore.com):
> On Fri, 1 Feb 2013 10:24:13 -0600
> Serge Hallyn <serge.hallyn at canonical.com> wrote:
> 
> > 
> > Did you actually test with a memory hog program? I just noticed there
> > appears to be a bug in that if I
> > 
> > 	d=/sys/fs/cgroup/memory/a
> > 	mkdir $d
> > 	echo 1 > $d/memory.use_hierarchy
> > 	echo 5000 > $d/memory.limit_in_bytes
> > 	mkdir $d/b
> > 
> > then $d/b/memory.limit_in_bytes does not report the reduced limit.  However
> > whenI run a program which does char *c = malloc(10000) after doing
> > 	echo $$ > $d/b/tasks
> > 
> > then I get killed by OOM.
> > 
> > -serge
> 
> I tested with a large array in ipython. Though, from your example, it seems I'm missing memory.use_hierarchy.
> 
> In principle, it seems like I need something like:
> 
> echo 1 > /sys/fs/cgroup/memory/lxc/memory.use_hierarchy
> 
> But, I can't do that before the container is started (no lxc directory) or after it is started (device busy).
> 

Yup, it looks like lxc ought to set that at startup.  I can think of
absolutely no cases where we would *not* want that done.  Something
like:

Subject: [PATCH 1/1] Try to enable memory cgroup use_hierarchy option.

The memory cgroup has a 'memory.use_hierarchy' which is initialized to
0.  It needs to be set to 1 at our top level, that is
/sys/fs/cgroup/memory/lxc/memory.use_hiararchy, before we create any
containers.  After the fact is too late.

Signed-off-by: Serge Hallyn <serge.hallyn at ubuntu.com>
---
 src/lxc/cgroup.c | 41 +++++++++++++++++++++++++++++++++++++++++
 1 file changed, 41 insertions(+)

diff --git a/src/lxc/cgroup.c b/src/lxc/cgroup.c
index 28f3474..0078eda 100644
--- a/src/lxc/cgroup.c
+++ b/src/lxc/cgroup.c
@@ -482,6 +482,43 @@ int try_to_move_cgname(char *cgparent, char *cgname)
 }
 
 /*
+ * The memory cgroup has a 'memory.use_hierarchy' which is initialized to
+ * 0.  It needs to be set to 1 at our top level, that is
+ * /sys/fs/cgroup/memory/lxc/memory.use_hiararchy, before we create any
+ * containers.  After the fact is too late.
+ */
+static int enable_hierarchy(char *path)
+{
+	char filepath[MAXPATHLEN];
+	int ret;
+	FILE *f;
+	int len = strlen(path);
+
+	if (strlen(path) < 7 || strcmp(&path[len-6], "memory") != 0)
+		return 0;
+
+	ret = snprintf(filepath, MAXPATHLEN, "%s/memory.use_hierarchy");
+	if (ret < 0 || ret >= MAXPATHLEN) {
+		SYSERROR("Failed creating memory hierarchy filepath name");
+		return -1;
+	}
+
+	f = fopen(filepath, "w");
+	if (!f) {
+		/* kernel may not support this file - s'ok */
+		WARN("Unable to open cgroup memory.use_hierarchy file");
+		return 0;
+	}
+
+	if (fprintf(f, "1") < 1) {
+		WARN("Unable to set hierarchy to true for memory cgroup");
+	}
+	fclose(f);
+
+	return 0;
+}
+
+/*
  * create a cgroup for the container in a particular subsystem.
  */
 static int lxc_one_cgroup_create(const char *name,
@@ -510,6 +547,10 @@ static int lxc_one_cgroup_create(const char *name,
 		SYSERROR("Failed creating pathname for cgroup parent (%d)\n", ret);
 		return -1;
 	}
+
+	if (enable_hierarchy(cgparent))
+		return -1;
+
 	ret = snprintf(cgname, MAXPATHLEN, "%s/%s", cgparent, name);
 	if (ret < 0 || ret >= MAXPATHLEN) {
 		SYSERROR("Failed creating pathname for cgroup (%d)\n", ret);
-- 
1.8.0


-serge