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support cgroup v1 mounted with noprefix #4513

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support cgroup v1 mounted with noprefix #4513

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tomaszduda23
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@tomaszduda23 tomaszduda23 commented Nov 5, 2024 •
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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

@tomaszduda23 tomaszduda23 force-pushed the groupv1 branch 3 times, most recently from 8a4edae to da51e85 Compare November 5, 2024 19:06
@tomaszduda23 tomaszduda23 mentioned this pull request Nov 5, 2024
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kolyshkin
kolyshkin reviewed Nov 6, 2024
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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.

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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.

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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.

@tomaszduda23 tomaszduda23 force-pushed the groupv1 branch 2 times, most recently from 7983199 to 9e8dc7b Compare November 6, 2024 18:18
kolyshkin
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The commit message needs to be updated to explain what is going on and why.

kolyshkin
kolyshkin requested changes Dec 5, 2024
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@tomaszduda23 tomaszduda23 force-pushed the groupv1 branch 4 times, most recently from 2e7eb64 to bbb3244 Compare December 8, 2024 20:57
@tomaszduda23
support cgroup v1 mounted with noprefix
d2d16c5 
Android mounts the v1 cpuset cgroup with the noprefix option.
As a result, runc first attempts to access cpuset files using the prefix format (e.g., cpuset.cpus).
If this fails, it falls back to accessing them without the prefix (e.g., cpus).
Once a successful access method is determined, it is cached and used for all subsequent operations.
Only the v1 cpuset cgroup is allowed to mount with noprefix. See kernel source:
https://github.com/torvalds/linux/blob/2e1b3cc9d7f790145a80cb705b168f05dab65df2/kernel/cgroup/cgroup-v1.c#L1070.
Cpuset cannot be mounted with and without prefix simultaneously.

Signed-off-by: Tomasz Duda <[email protected]>
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