[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 03/11] cgroup/blkio: Add deprecation messages to reset_stats

[Michal Koutný]

It is difficult to sync with stat updaters, stats are (should be)
monotonic so users can calculate differences from a reference.

Signed-off-by: Michal Koutný <mkoutny@suse.com>
---
 block/blk-cgroup.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/block/blk-cgroup.c b/block/blk-cgroup.c
index 9ed93d91d754a..1464c968eeb0c 100644
--- a/block/blk-cgroup.c
+++ b/block/blk-cgroup.c
@@ -659,6 +659,7 @@ static int blkcg_reset_stats(struct cgroup_subsys_state *css,
 	struct blkcg_gq *blkg;
 	int i;
 
+	pr_info_once("blkio.%s is deprecated\n", cftype->name);
 	mutex_lock(&blkcg_pol_mutex);
 	spin_lock_irq(&blkcg->lock);
 
-- 
2.48.1

[PATCH v2 11/11] blk-cgroup: Simplify policy files registration

[Michal Koutný]

Use one set of files when there is no difference between default and
legacy files, similar to regular subsys files registration. No
functional change.

Signed-off-by: Michal Koutný <mkoutny@suse.com>
---
 block/blk-cgroup.c     |  7 +++++--
 block/blk-ioprio.c     | 23 +++++++----------------
 include/linux/cgroup.h |  1 +
 kernel/cgroup/cgroup.c |  2 +-
 4 files changed, 14 insertions(+), 19 deletions(-)

diff --git a/block/blk-cgroup.c b/block/blk-cgroup.c
index 1464c968eeb0c..1994a11ff9034 100644
--- a/block/blk-cgroup.c
+++ b/block/blk-cgroup.c
@@ -1771,12 +1771,15 @@ int blkcg_policy_register(struct blkcg_policy *pol)
 	mutex_unlock(&blkcg_pol_mutex);
 
 	/* everything is in place, add intf files for the new policy */
-	if (pol->dfl_cftypes)
+	if (pol->dfl_cftypes == pol->legacy_cftypes) {
+		WARN_ON(cgroup_add_cftypes(&io_cgrp_subsys,
+					   pol->dfl_cftypes));
+	} else {
 		WARN_ON(cgroup_add_dfl_cftypes(&io_cgrp_subsys,
 					       pol->dfl_cftypes));
-	if (pol->legacy_cftypes)
 		WARN_ON(cgroup_add_legacy_cftypes(&io_cgrp_subsys,
 						  pol->legacy_cftypes));
+	}
 	mutex_unlock(&blkcg_pol_register_mutex);
 	return 0;
 
diff --git a/block/blk-ioprio.c b/block/blk-ioprio.c
index 8fff7ccc0ac73..13659dc15c3ff 100644
--- a/block/blk-ioprio.c
+++ b/block/blk-ioprio.c
@@ -113,27 +113,18 @@ static void ioprio_free_cpd(struct blkcg_policy_data *cpd)
 	kfree(blkcg);
 }
 
-#define IOPRIO_ATTRS						\
-	{							\
-		.name		= "prio.class",			\
-		.seq_show	= ioprio_show_prio_policy,	\
-		.write		= ioprio_set_prio_policy,	\
-	},							\
-	{ } /* sentinel */
-
-/* cgroup v2 attributes */
 static struct cftype ioprio_files[] = {
-	IOPRIO_ATTRS
-};
-
-/* cgroup v1 attributes */
-static struct cftype ioprio_legacy_files[] = {
-	IOPRIO_ATTRS
+	{
+		.name		= "prio.class",
+		.seq_show	= ioprio_show_prio_policy,
+		.write		= ioprio_set_prio_policy,
+	},
+	{ } /* sentinel */
 };
 
 static struct blkcg_policy ioprio_policy = {
 	.dfl_cftypes	= ioprio_files,
-	.legacy_cftypes = ioprio_legacy_files,
+	.legacy_cftypes = ioprio_files,
 
 	.cpd_alloc_fn	= ioprio_alloc_cpd,
 	.cpd_free_fn	= ioprio_free_cpd,
diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h
index f8ef47f8a634d..8e7415c64ed1d 100644
--- a/include/linux/cgroup.h
+++ b/include/linux/cgroup.h
@@ -113,6 +113,7 @@ int cgroup_transfer_tasks(struct cgroup *to, struct cgroup *from);
 
 int cgroup_add_dfl_cftypes(struct cgroup_subsys *ss, struct cftype *cfts);
 int cgroup_add_legacy_cftypes(struct cgroup_subsys *ss, struct cftype *cfts);
+int cgroup_add_cftypes(struct cgroup_subsys *ss, struct cftype *cfts);
 int cgroup_rm_cftypes(struct cftype *cfts);
 void cgroup_file_notify(struct cgroup_file *cfile);
 void cgroup_file_show(struct cgroup_file *cfile, bool show);
diff --git a/kernel/cgroup/cgroup.c b/kernel/cgroup/cgroup.c
index 3a5af0fc544a6..e93b0563a8964 100644
--- a/kernel/cgroup/cgroup.c
+++ b/kernel/cgroup/cgroup.c
@@ -4447,7 +4447,7 @@ int cgroup_rm_cftypes(struct cftype *cfts)
  * function currently returns 0 as long as @cfts registration is successful
  * even if some file creation attempts on existing cgroups fail.
  */
-static int cgroup_add_cftypes(struct cgroup_subsys *ss, struct cftype *cfts)
+int cgroup_add_cftypes(struct cgroup_subsys *ss, struct cftype *cfts)
 {
 	int ret;
 
-- 
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