Reading cgroups.txt and casting around the net leads me to believe that it is
possible to attach a cgroup subsystem (e.g. memory) to multiple hierarchies,
but this seems to result in “mirrored” hierarchies which are automatically kept
in step with each other - essentially it looks like the same hierarchy at
multiple file system paths.
Take the following interaction for example:
\begin{verbatim}
$ pwd
/home/vagrant
$ mkdir mem1
$ mkdir mem2
$ sudo su
# mount -t cgroup -o memory none /home/vagrant/mem1
# mount -t cgroup -o memory none /home/vagrant/mem2
# cd mem1
# mkdir inst1
# ls inst1
cgroup.clone_children memory.failcnt ...
# ls ../mem2
cgroup.clone_children inst1 memory.limit_in_bytes ...
# cd inst1
# echo 1000000 > memory.limit_in_bytes
# cat memory.limit_in_bytes
1003520
# cat ../../mem2/inst1/memory.limit_in_bytes
1003520
# echo $$ > tasks
# cat tasks
1365
1409
# cat ../../mem2/inst1/tasks
1365
1411
Is this working as intended? Is there some other way to attach a subsystem to
*distinct* hierarchies? Distinct hierarchies would allow distinct cgroups,
distinct settings (e.g. memory.limit_in_bytes) and distinct partitions of the
tasks in the system.
Note: I don’t have a good use for this function - I’m simply trying to reverse
engineer the semantics of cgroups to get a precise understanding.
Glyn--
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