[PATCH v2 00/11] cgroup v1 deprecation messages

[PATCH v2 00/11] cgroup v1 deprecation messages

[Michal Koutný]

Memory controller had begun to print warning messages when using some
attributes that do no have a counterpart in its cgroup v2
implementation. This is informative to users who run (unwittingly) on v1
or to distros that run v1 (they can learn about such users or prepare
for disabling v1 configs).

I consider the deprecated files in three categories:
  - RE) replacement exists,
  - DN) dropped as non-ideal concept (e.g. non-hierarchical resources),
  - NE) not evaluated (yet).

For RE, I added the replacement into the warning message, DN have only a
plain deprecation message and I marked the commits with NE as RFC.
Also I'd be happy if you would point out some forgotten knobs that'd
deserve similar warnings.

The level of messages is info to avoid too much noise (may be increased
in future when there are fewer users). Some knobs from DN have warn
level.

The net_cls and net_prio controllers that only exist on v1 hierarchies
have no straightforward action for users (replacement would rely on net
NS or eBPF), so messages for their usage are omitted, although it'd be
good to eventually retire that code in favor of aforementioned.

At the end are some cleanup patches I encountered en route.

Changes from v1 (https://lore.kernel.org/r/20250304153801.597907-1-mkoutny@suse.com/)
- cpuset load_balance/pressure warn wording (Waiman)
- comment typo (Waiman)
- collect Acks
- drop bouncing Cc: and respective RFC (self)
- change level warn -> info, except for spread slab (Tejun)
- add memory.swappiness (self)
- add legacy freezer message (self)
- update cover wrt net* controllers (self)

Michal Koutný (11):
  cgroup/cpuset-v1: Add deprecation messages to sched_load_balance and
    memory_pressure_enabled
  cgroup/cpuset-v1: Add deprecation messages to memory_spread_page and
    memory_spread_slab
  cgroup/blkio: Add deprecation messages to reset_stats
  cgroup: Print message when /proc/cgroups is read on v2-only system
  cgroup/cpuset-v1: Add deprecation messages to mem_exclusive and
    mem_hardwall
  cgroup/cpuset-v1: Add deprecation messages to memory_migrate
  RFC cgroup/cpuset-v1: Add deprecation messages to
    sched_relax_domain_level
  mm: Add transformation message for per-memcg swappiness
  cgroup: Add deprecation message to legacy freezer controller
  cgroup: Update file naming comment
  blk-cgroup: Simplify policy files registration

 .../cgroup-v1/freezer-subsystem.rst           |  4 ++++
 .../admin-guide/cgroup-v1/memory.rst          |  1 +
 block/blk-cgroup.c                            |  8 +++++--
 block/blk-ioprio.c                            | 23 ++++++-------------
 include/linux/cgroup-defs.h                   |  5 ++--
 include/linux/cgroup.h                        |  1 +
 kernel/cgroup/cgroup-internal.h               |  1 +
 kernel/cgroup/cgroup-v1.c                     |  7 ++++++
 kernel/cgroup/cgroup.c                        |  4 ++--
 kernel/cgroup/cpuset-v1.c                     |  8 +++++++
 kernel/cgroup/legacy_freezer.c                |  6 +++--
 mm/memcontrol-v1.c                            |  6 +++--
 12 files changed, 47 insertions(+), 27 deletions(-)


base-commit: 80e54e84911a923c40d7bee33a34c1b4be148d7a
-- 
2.48.1

[PATCH v2 08/11] mm: Add transformation message for per-memcg swappiness

[Michal Koutný]

The concept of per-memcg swappiness has never landed well in memcg for
cgroup v2. Add a message to users who use it on v1 hierarchy.
Decreased swappiness transforms to memory.swap.max=0 whereas
increased swappiness transforms into active memory.reclaim operation.

Link: https://lore.kernel.org/r/1577252208-32419-1-git-send-email-teawater@gmail.com/
Signed-off-by: Michal Koutný <mkoutny@suse.com>
---
 Documentation/admin-guide/cgroup-v1/memory.rst | 1 +
 mm/memcontrol-v1.c                             | 6 ++++--
 2 files changed, 5 insertions(+), 2 deletions(-)

diff --git a/Documentation/admin-guide/cgroup-v1/memory.rst b/Documentation/admin-guide/cgroup-v1/memory.rst
index 286d16fc22ebb..02b8206a35941 100644
--- a/Documentation/admin-guide/cgroup-v1/memory.rst
+++ b/Documentation/admin-guide/cgroup-v1/memory.rst
@@ -90,6 +90,7 @@ Brief summary of control files.
                                      used.
  memory.swappiness		     set/show swappiness parameter of vmscan
 				     (See sysctl's vm.swappiness)
+				     Per memcg knob does not exist in cgroup v2.
  memory.move_charge_at_immigrate     This knob is deprecated.
  memory.oom_control		     set/show oom controls.
                                      This knob is deprecated and shouldn't be
diff --git a/mm/memcontrol-v1.c b/mm/memcontrol-v1.c
index 2be6b9112808c..29ca6489b4ff7 100644
--- a/mm/memcontrol-v1.c
+++ b/mm/memcontrol-v1.c
@@ -1855,9 +1855,11 @@ static int mem_cgroup_swappiness_write(struct cgroup_subsys_state *css,
 	if (val > MAX_SWAPPINESS)
 		return -EINVAL;
 
-	if (!mem_cgroup_is_root(memcg))
+	if (!mem_cgroup_is_root(memcg)) {
+		pr_info_once("Per memcg swappiness does not exist in cgroup v2. "
+			     "See memory.reclaim or memory.swap.max there\n ")
 		WRITE_ONCE(memcg->swappiness, val);
-	else
+	} else
 		WRITE_ONCE(vm_swappiness, val);
 
 	return 0;
-- 
2.48.1

Re: [PATCH v2 00/11] cgroup v1 deprecation messages

[Jens Axboe]

> Memory controller had begun to print warning messages when using some
> attributes that do no have a counterpart in its cgroup v2
> implementation. This is informative to users who run (unwittingly) on v1
> or to distros that run v1 (they can learn about such users or prepare
> for disabling v1 configs).
>
> I consider the deprecated files in three categories:
>   - RE) replacement exists,
>   - DN) dropped as non-ideal concept (e.g. non-hierarchical resources),
>   - NE) not evaluated (yet).
>
> For RE, I added the replacement into the warning message, DN have only a
> plain deprecation message and I marked the commits with NE as RFC.
> Also I'd be happy if you would point out some forgotten knobs that'd
> deserve similar warnings.
>
> The level of messages is info to avoid too much noise (may be increased
> in future when there are fewer users). Some knobs from DN have warn
> level.
>
> The net_cls and net_prio controllers that only exist on v1 hierarchies
> have no straightforward action for users (replacement would rely on net
> NS or eBPF), so messages for their usage are omitted, although it'd be
> good to eventually retire that code in favor of aforementioned.
>
> At the end are some cleanup patches I encountered en route.

For the block related parts, as I'm assuming Tejun will pick this up:

Acked-by: Jens Axboe <axboe@kernel.dk>

-- 
Jens Axboe

Re: [PATCH v2 00/11] cgroup v1 deprecation messages

[Tejun Heo]

On Tue, Mar 11, 2025 at 01:36:17PM +0100, Michal Koutný wrote:
> Memory controller had begun to print warning messages when using some
> attributes that do no have a counterpart in its cgroup v2
> implementation. This is informative to users who run (unwittingly) on v1
> or to distros that run v1 (they can learn about such users or prepare
> for disabling v1 configs).
> 
> I consider the deprecated files in three categories:
>   - RE) replacement exists,
>   - DN) dropped as non-ideal concept (e.g. non-hierarchical resources),
>   - NE) not evaluated (yet).
> 
> For RE, I added the replacement into the warning message, DN have only a
> plain deprecation message and I marked the commits with NE as RFC.
> Also I'd be happy if you would point out some forgotten knobs that'd
> deserve similar warnings.
> 
> The level of messages is info to avoid too much noise (may be increased
> in future when there are fewer users). Some knobs from DN have warn
> level.
> 
> The net_cls and net_prio controllers that only exist on v1 hierarchies
> have no straightforward action for users (replacement would rely on net
> NS or eBPF), so messages for their usage are omitted, although it'd be
> good to eventually retire that code in favor of aforementioned.
> 
> At the end are some cleanup patches I encountered en route.

Applied to cgroup/for-6.15.

Thanks.

-- 
tejun