How to find out how much memory lxc container is allowed to consume?

Question

I'm trying to make ansible set InnoDB buffer pool size to some percent of available memory. But ansible_memtotal_mb and free report how much memory the host has. How do I figure out how much memory is available from inside container? Container name is not known in advance.

UPD I'm running debian jessie, and pass cgroup_enable=memory parameter to the kernel.

host
====

# lxc-checkconfig
Kernel configuration not found at /proc/config.gz; searching...
Kernel configuration found at /boot/config-3.16.0-4-amd64
--- Namespaces ---
Namespaces: enabled
Utsname namespace: enabled
Ipc namespace: enabled
Pid namespace: enabled
User namespace: enabled
Network namespace: enabled
Multiple /dev/pts instances: enabled

--- Control groups ---
Cgroup: enabled
Cgroup clone_children flag: enabled
Cgroup device: enabled
Cgroup sched: enabled
Cgroup cpu account: enabled
Cgroup memory controller: enabled
Cgroup cpuset: enabled

--- Misc ---
Veth pair device: enabled
Macvlan: enabled
Vlan: enabled
File capabilities: enabled

Note : Before booting a new kernel, you can check its configuration
usage : CONFIG=/path/to/config /usr/bin/lxc-checkconfig

# grep cgroup /var/lib/lxc/sta/config
lxc.cgroup.memory.limit_in_bytes = 1000M

# mount | grep memory
cgroup on /sys/fs/cgroup/memory type cgroup (rw,nosuid,nodev,noexec,relatime,memory)

# cd /sys/fs/cgroup/memory

# cat memory.limit_in_bytes
18446744073709551615

# cat lxc/sta/memory.limit_in_bytes
1048576000


container
=========

$ cat /proc/self/cgroup
9:perf_event:/lxc/sta
8:blkio:/
7:net_cls,net_prio:/lxc/sta
6:freezer:/lxc/sta
5:devices:/
4:memory:/
3:cpu,cpuacct:/
2:cpuset:/lxc/sta
1:name=systemd:/user.slice/user-0.slice/session-10304.scope/system.slice/ssh.service

# mount | grep memory
cgroup on /sys/fs/cgroup/memory type cgroup (rw,nosuid,nodev,noexec,relatime,memory)

# cd /sys/fs/cgroup/memory

# cat memory.limit_in_bytes
18446744073709551615

# cat lxc/sta/memory.limit_in_bytes
1048576000

Answer 1

tl;dr

cat /sys/fs/cgroup/memory$(cat /proc/self/cgroup | grep memory | cut -d: -f3)/memory.limit_in_bytes

or

cat $(mount | grep cgroup | grep memory | cut -d' ' -f3)$(cat /proc/self/cgroup | grep memory | cut -d: -f3)/memory.limit_in_bytes

If your default container configuration allows host's cgroup info from within container (based on lxc.mount.auto setting),you could simply parse cgroup info as shown below

Check your cgroup info from /proc/self/cgroup

root@my-firefox:/# grep memory /proc/self/cgroup 
4:memory:/cv/my-firefox

Now based on your cgroup mount point (could locate that from /proc/mounts), verify memory limit file content

root@my-firefox:/# cd /sys/fs/cgroup/memory/cv/my-firefox/
root@my-firefox:/sys/fs/cgroup/memory/cv/my-firefox# cat memory.limit_in_bytes 
268435456

In my case above, cgroup root was mounted at /sys/fs/cgroup so with that info and appending path /memory/cv/my-firefox, I could query all memory limits set for the container

This case the limit is 256M

PS: free & ansible_memtotal_mb are host based and they are not container aware. I am not aware of ansible, but I assume it would have something similar to facts in puppet, where you could write a custom fact to gather this info