Bug#793372: systemd breaks LXC cgroup memory limitations

[Pablo Abelenda]

Package: systemd
Version: 215-17+deb8u1
Severity: important

Dear Maintainer,

I have been checking on LXC for a while. I wanted to acquaint with the
containers management, specifically with the resources limitation
capabilities.

I have created, configured and destroyed several containers. The issue
comes when I try to limit the memory usage. I have added this option to
the grub defaults:

cgroup_enable=memory

This allowed me to start a container with options configured such as
this:

lxc.cgroup.memory.limit_in_bytes = 1024M
lxc.cgroup.memory.memsw.limit_in_bytes = 1200M

The thing is that when I try to use more than 1200 MB of memory, inside
the container, I actually can. I have used a very simply script I found
on someone page to test the memory allocation capabilities.

########################################
memory_allocation.py
########################################
#!/usr/bin/env python
import sys
import time

if len(sys.argv) != 2:
    print "usage: fillmem <number-of-megabytes>"
    sys.exit()

count = int(sys.argv[1])

megabyte = (0,) * (1024 * 1024 / 8)

data = megabyte * count

while True:
    time.sleep(1)
########################################

I have tried to isolate the problem, focusing on some missing LXC or
cgroups configuration. Let me add the trace:

First, I have created a new control group, outside the LXC stuff:

cgcreate -g memory:/bmalloc1gb
echo $(( 1024 * 1024 * 1024 ))|tee /sys/fs/cgroup/memory/bmalloc1gb/memory.limit_in_bytes
echo $(( 1200 * 1024 * 1024 ))|tee /sys/fs/cgroup/memory/bmalloc1gb/memory.memsw.limit_in_bytes
cgexec -g memory:/bmalloc1gb bash
python memory_allocation.py 2000 [killed]

When I run the script on this environment, the memory allocation did not
went far from this 1200 MB, which is what I need.

Second, I have joined the LXC cgroup, to try the very same as above:

cgexec -g memory:lxc/test bash
python memory_allocation.py 2000 [killed]

This two tests made me point to LXC, but after some internet digging I
found this:

https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=777601

In this bug report, which is not exactly the same as this one, the
reporter states this:

"I also tested something which may be another problem (so another ticket)
but the memory and swap limitation doesn't work at all :-(...with or
without this bug. I can't tell if it's linked or not.
I tested cpu pinning and it works like a charm. The issue seems related
to memory and swap only."

After this income information, I have switched back both the host and
the container, to sysvinit. With the systems booted on sysvinit, the
memory limitation is working as it is expected.

Let me add the whole container configuration for your reference:

lxc.cgroup.cpuset.cpus = 0,1
lxc.cgroup.cpu.shares = 256
lxc.cgroup.blkio.weight = 500
lxc.cgroup.memory.limit_in_bytes = 1024M
lxc.cgroup.memory.memsw.limit_in_bytes = 1200M
lxc.network.type = veth
lxc.network.flags = up
lxc.network.link = br0
lxc.network.name = eth0
lxc.rootfs = /dev/vg/test
lxc.start.auto = 1
lxc.include = /usr/share/lxc/config/debian.common.conf
lxc.mount = /var/lib/lxc/test/fstab
lxc.utsname = test
lxc.arch = amd64
lxc.autodev = 1

Thanks for your consideration.

Best regards.


-- Package-specific info:

-- System Information:
Debian Release: 8.1
  APT prefers stable-updates
  APT policy: (500, 'stable-updates'), (500, 'stable')
Architecture: amd64 (x86_64)

Kernel: Linux 3.16.0-4-amd64 (SMP w/4 CPU cores)
Locale: LANG=en_US.UTF-8, LC_CTYPE=en_US.UTF-8 (charmap=UTF-8)
Shell: /bin/sh linked to /bin/dash
Init: systemd (via /run/systemd/system)

Versions of packages systemd depends on:
ii  acl             2.2.52-2
ii  adduser         3.113+nmu3
ii  initscripts     2.88dsf-59
ii  libacl1         2.2.52-2
ii  libaudit1       1:2.4-1+b1
ii  libblkid1       2.25.2-6
ii  libc6           2.19-18
ii  libcap2         1:2.24-8
ii  libcap2-bin     1:2.24-8
ii  libcryptsetup4  2:1.6.6-5
ii  libgcrypt20     1.6.3-2
ii  libkmod2        18-3
ii  liblzma5        5.1.1alpha+20120614-2+b3
ii  libpam0g        1.1.8-3.1
ii  libselinux1     2.3-2
ii  libsystemd0     215-17+deb8u1
ii  mount           2.25.2-6
ii  sysv-rc         2.88dsf-59
ii  udev            215-17+deb8u1
ii  util-linux      2.25.2-6

Versions of packages systemd recommends:
ii  dbus            1.8.18-0+deb8u1
ii  libpam-systemd  215-17+deb8u1

Versions of packages systemd suggests:
pn  systemd-ui  <none>

-- no debconf information