support cgroup v1 mounted with noprefix

[tomaszduda23]

Android mounts cgroup v1 with noprefix. Related to #4443

# mount | grep cgroup
none on /dev/blkio type cgroup (rw,nosuid,nodev,noexec,relatime,blkio)
none on /dev/cpuctl type cgroup (rw,nosuid,nodev,noexec,relatime,cpu)
none on /dev/cpuset type cgroup (rw,nosuid,nodev,noexec,relatime,cpuset,noprefix,release_agent=/sbin/cpuset_release_agent)
none on /dev/memcg type cgroup (rw,nosuid,nodev,noexec,relatime,memory)
none on /dev/stune type cgroup (rw,nosuid,nodev,noexec,relatime,schedtune)
none on /sys/fs/cgroup type cgroup2 (rw,nosuid,nodev,noexec,relatime)

ls -l /dev/cpuset
total 0
drwxr-xr-x. 2 system system 0 May 29  1970 background
drwxr-xr-x. 2 system system 0 May 29  1970 camera-daemon
-rw-r--r--. 1 root   root   0 Nov  5 19:48 cgroup.clone_children
-rw-rw-r--. 1 system system 0 May 29  1970 cgroup.procs
-r--r--r--. 1 root   root   0 Nov  5 19:48 cgroup.sane_behavior
-rw-r--r--. 1 root   root   0 Nov  5 19:48 cpu_exclusive
-rw-r--r--. 1 root   root   0 May 29  1970 cpus
-r--r--r--. 1 root   root   0 Nov  5 19:48 effective_cpus
-r--r--r--. 1 root   root   0 Nov  5 19:48 effective_mems
drwxr-xr-x. 2 system system 0 May 29  1970 foreground
-rw-r--r--. 1 root   root   0 Nov  5 19:48 mem_exclusive
-rw-r--r--. 1 root   root   0 Nov  5 19:48 mem_hardwall
-rw-r--r--. 1 root   root   0 Nov  5 19:48 memory_migrate
-r--r--r--. 1 root   root   0 Nov  5 19:48 memory_pressure
-rw-r--r--. 1 root   root   0 Nov  5 19:48 memory_pressure_enabled
-rw-r--r--. 1 root   root   0 Nov  5 19:48 memory_spread_page
-rw-r--r--. 1 root   root   0 Nov  5 19:48 memory_spread_slab
-rw-r--r--. 1 root   root   0 May 29  1970 mems
-rw-r--r--. 1 root   root   0 Nov  5 19:48 notify_on_release
-rw-r--r--. 1 root   root   0 Nov  5 19:48 release_agent
drwxr-xr-x. 2 system system 0 May 29  1970 restricted
-rw-r--r--. 1 root   root   0 Nov  5 19:48 sched_load_balance
-rw-r--r--. 1 root   root   0 Nov  5 19:48 sched_relax_domain_level
drwxrwxr-x. 2 system system 0 May 29  1970 system-background
-rw-rw-r--. 1 system system 0 May 29  1970 tasks
drwxr-xr-x. 2 system system 0 May 29  1970 top-app

[kolyshkin]

In general, cgroup v1 is being phased out slowly, and we'd rather not add more functionality in this area.

I'm pretty sure Android is going to switch to cgroup v2 soon, if not yet.

[kolyshkin]

I'm pretty sure Android is going to switch to cgroup v2 soon, if not yet.

I see that even the latest and greatest Android 15 still uses cgroup v1 for a few specific controllers (although there are only 3 that I see on my phone, and only cpuset is mounted with noprefix flag).

Yet, I see there's cgroup2 mounted at /sys/fs/cgroup. Why not use it, it should be pretty standard.

[tomaszduda23]

In general, cgroup v1 is being phased out slowly, and we'd rather not add more functionality in this area.

Usually Android use older kernels. The support for cgroup v2 is limited there. I've two phones with Android 13 and 14 and both are on kernel 4.19. Android was updated a few times but kernel version stay the same.

Yet, I see there's cgroup2 mounted at /sys/fs/cgroup. Why not use it, it should be pretty standard.

I tried that approach too. It doesn't work since it would require newer kernel which is not available for many devices.