1. Prepare the cgroups 
# mount -t tmpfs none /sys/fs/cgroup
# mkdir /sys/fs/cgroup/memory
# mount -t cgroup none /sys/fs/cgroup/memory -o memory

2. Make the new group and move pid(s) into it
# mkdir /sys/fs/cgroup/memory/0
# echo $$ > /sys/fs/cgroup/memory/0/tasks

NOTE: in this example, only pid of current bash shell

Since now we're in the 0 cgroup, we can alter the memory limit:
# echo 4M > /sys/fs/cgroup/memory/0/memory.limit_in_bytes

NOTE: We can use an optional suffix (k, K, m, M, g or G)

We can check the limit:
# cat /sys/fs/cgroup/memory/0/memory.limit_in_bytes
4194304

We can check the usage:
# cat /sys/fs/cgroup/memory/0/memory.usage_in_bytes
1216512

3. Swap Extension

 - memory.memsw.usage_in_bytes.
 - memory.memsw.limit_in_bytes.

memsw means memory+swap.

Example: Assume a system with 4G of swap. A task which allocates 6G of memory
(by mistake) under 2G memory limitation will use all swap.
In this case, setting memsw.limit_in_bytes=3G will prevent bad use of swap.
By using the memsw limit, you can avoid system OOM which can be caused by swap
shortage.

#EOF ha ha :)