[PATCH] cpuset: introduce non-blocking cpuset.mems setting option

[PATCH] cpuset: introduce non-blocking cpuset.mems setting option

[Zhongkun He]

Setting the cpuset.mems in cgroup v2 can trigger memory
migrate in cpuset. This behavior is fine for newly created
cgroups but it can cause issues for the existing cgroups.
In our scenario, modifying the cpuset.mems setting during
peak times frequently leads to noticeable service latency
or stuttering.

It is important to have a consistent set of behavior for
both cpus and memory. But it does cause issues at times,
so we would like to have a flexible option.

This idea is from the non-blocking limit setting option in
memory control.

https://lore.kernel.org/all/20250506232833.3109790-1-shakeel.butt@linux.dev/

Signed-off-by: Zhongkun He <hezhongkun.hzk@bytedance.com>
---
 Documentation/admin-guide/cgroup-v2.rst | 7 +++++++
 kernel/cgroup/cpuset-internal.h         | 6 ++++++
 kernel/cgroup/cpuset.c                  | 7 +++++++
 3 files changed, 20 insertions(+)

diff --git a/Documentation/admin-guide/cgroup-v2.rst b/Documentation/admin-guide/cgroup-v2.rst
index 1a16ce68a4d7..d9e8e2a770af 100644
--- a/Documentation/admin-guide/cgroup-v2.rst
+++ b/Documentation/admin-guide/cgroup-v2.rst
@@ -2408,6 +2408,13 @@ Cpuset Interface Files
 	a need to change "cpuset.mems" with active tasks, it shouldn't
 	be done frequently.
 
+	If cpuset.mems is opened with O_NONBLOCK then the migration is
+	bypassed. This is useful for admin processes that need to adjust
+	the cpuset.mems dynamically without blocking. However, there is
+	a risk that previously allocated pages are not within the new
+	cpuset.mems range, which may be altered by move_pages syscall or
+	numa_balance.
+
   cpuset.mems.effective
 	A read-only multiple values file which exists on all
 	cpuset-enabled cgroups.
diff --git a/kernel/cgroup/cpuset-internal.h b/kernel/cgroup/cpuset-internal.h
index 383963e28ac6..5686bb08c4fe 100644
--- a/kernel/cgroup/cpuset-internal.h
+++ b/kernel/cgroup/cpuset-internal.h
@@ -162,6 +162,9 @@ struct cpuset {
 	/* partition root state */
 	int partition_root_state;
 
+	/* Do not migrate memory when modifying cpuset.mems this time */
+	bool skip_migration_once;
+
 	/*
 	 * number of SCHED_DEADLINE tasks attached to this cpuset, so that we
 	 * know when to rebuild associated root domain bandwidth information.
@@ -227,6 +230,9 @@ static inline int is_sched_load_balance(const struct cpuset *cs)
 
 static inline int is_memory_migrate(const struct cpuset *cs)
 {
+	if (cs->skip_migration_once)
+		return 0;
+
 	return test_bit(CS_MEMORY_MIGRATE, &cs->flags);
 }
 
diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
index 24b70ea3e6ce..f43d7b291cde 100644
--- a/kernel/cgroup/cpuset.c
+++ b/kernel/cgroup/cpuset.c
@@ -3208,7 +3208,14 @@ ssize_t cpuset_write_resmask(struct kernfs_open_file *of,
 		retval = update_exclusive_cpumask(cs, trialcs, buf);
 		break;
 	case FILE_MEMLIST:
+		if (of->file->f_flags & O_NONBLOCK)
+			cs->skip_migration_once = true;
+
 		retval = update_nodemask(cs, trialcs, buf);
+
+		/* Restore skip_migration */
+		if (cs->skip_migration_once)
+			cs->skip_migration_once = false;
 		break;
 	default:
 		retval = -EINVAL;
-- 
2.39.5

Re: [PATCH] cpuset: introduce non-blocking cpuset.mems setting option

[Tejun Heo]

On Wed, May 21, 2025 at 11:45:27AM +0800, Zhongkun He wrote:
> Setting the cpuset.mems in cgroup v2 can trigger memory
> migrate in cpuset. This behavior is fine for newly created
> cgroups but it can cause issues for the existing cgroups.
> In our scenario, modifying the cpuset.mems setting during
> peak times frequently leads to noticeable service latency
> or stuttering.
> 
> It is important to have a consistent set of behavior for
> both cpus and memory. But it does cause issues at times,
> so we would like to have a flexible option.
> 
> This idea is from the non-blocking limit setting option in
> memory control.
> 
> https://lore.kernel.org/all/20250506232833.3109790-1-shakeel.butt@linux.dev/
> 
> Signed-off-by: Zhongkun He <hezhongkun.hzk@bytedance.com>
> ---
>  Documentation/admin-guide/cgroup-v2.rst | 7 +++++++
>  kernel/cgroup/cpuset-internal.h         | 6 ++++++
>  kernel/cgroup/cpuset.c                  | 7 +++++++
>  3 files changed, 20 insertions(+)
> 
> diff --git a/Documentation/admin-guide/cgroup-v2.rst b/Documentation/admin-guide/cgroup-v2.rst
> index 1a16ce68a4d7..d9e8e2a770af 100644
> --- a/Documentation/admin-guide/cgroup-v2.rst
> +++ b/Documentation/admin-guide/cgroup-v2.rst
> @@ -2408,6 +2408,13 @@ Cpuset Interface Files
>  	a need to change "cpuset.mems" with active tasks, it shouldn't
>  	be done frequently.
>  
> +	If cpuset.mems is opened with O_NONBLOCK then the migration is
> +	bypassed. This is useful for admin processes that need to adjust
> +	the cpuset.mems dynamically without blocking. However, there is
> +	a risk that previously allocated pages are not within the new
> +	cpuset.mems range, which may be altered by move_pages syscall or
> +	numa_balance.

As said in the other thread, nack on this approach.

Thanks.

-- 
tejun

[PATCH] cpuset: introduce non-blocking cpuset.mems setting option

[Zhongkun He]

Setting the cpuset.mems in cgroup v2 can trigger memory
migrate in cpuset. This behavior is fine for newly created
cgroups but it can cause issues for the existing cgroups.
In our scenario, modifying the cpuset.mems setting during
peak times frequently leads to noticeable service latency
or stuttering.

It is important to have a consistent set of behavior for
both cpus and memory. But it does cause issues at times,
so we would hope to have a flexible option.

This idea is from the non-blocking limit setting option in
memory control.

https://lore.kernel.org/all/20250506232833.3109790-1-shakeel.butt@linux.dev/

Signed-off-by: Zhongkun He <hezhongkun.hzk@bytedance.com>
---
 Documentation/admin-guide/cgroup-v2.rst |  7 +++++++
 kernel/cgroup/cpuset.c                  | 11 +++++++++++
 2 files changed, 18 insertions(+)

diff --git a/Documentation/admin-guide/cgroup-v2.rst b/Documentation/admin-guide/cgroup-v2.rst
index 1a16ce68a4d7..d9e8e2a770af 100644
--- a/Documentation/admin-guide/cgroup-v2.rst
+++ b/Documentation/admin-guide/cgroup-v2.rst
@@ -2408,6 +2408,13 @@ Cpuset Interface Files
 	a need to change "cpuset.mems" with active tasks, it shouldn't
 	be done frequently.
 
+	If cpuset.mems is opened with O_NONBLOCK then the migration is
+	bypassed. This is useful for admin processes that need to adjust
+	the cpuset.mems dynamically without blocking. However, there is
+	a risk that previously allocated pages are not within the new
+	cpuset.mems range, which may be altered by move_pages syscall or
+	numa_balance.
+
   cpuset.mems.effective
 	A read-only multiple values file which exists on all
 	cpuset-enabled cgroups.
diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
index 24b70ea3e6ce..2a0867e0c6d2 100644
--- a/kernel/cgroup/cpuset.c
+++ b/kernel/cgroup/cpuset.c
@@ -3208,7 +3208,18 @@ ssize_t cpuset_write_resmask(struct kernfs_open_file *of,
 		retval = update_exclusive_cpumask(cs, trialcs, buf);
 		break;
 	case FILE_MEMLIST:
+		bool skip_migrate_once = false;
+
+		if ((of->file->f_flags & O_NONBLOCK) &&
+			is_memory_migrate(cs) &&
+			!cpuset_update_flag(CS_MEMORY_MIGRATE, cs, 0))
+			skip_migrate_once = true;
+
 		retval = update_nodemask(cs, trialcs, buf);
+
+		/* Restore the migrate flag */
+		if (skip_migrate_once)
+			cpuset_update_flag(CS_MEMORY_MIGRATE, cs, 1);
 		break;
 	default:
 		retval = -EINVAL;
-- 
2.39.5

Re: [PATCH] cpuset: introduce non-blocking cpuset.mems setting option

[kernel test robot]

Hi Zhongkun,

kernel test robot noticed the following build errors:

[auto build test ERROR on tj-cgroup/for-next]
[also build test ERROR on linus/master v6.15-rc7 next-20250516]
[If your patch is applied to the wrong git tree, kindly drop us a note.
And when submitting patch, we suggest to use '--base' as documented in
https://git-scm.com/docs/git-format-patch#_base_tree_information]

url:    https://github.com/intel-lab-lkp/linux/commits/Zhongkun-He/cpuset-introduce-non-blocking-cpuset-mems-setting-option/20250520-111737
base:   https://git.kernel.org/pub/scm/linux/kernel/git/tj/cgroup.git for-next
patch link:    https://lore.kernel.org/r/20250520031552.1931598-1-hezhongkun.hzk%40bytedance.com
patch subject: [PATCH] cpuset: introduce non-blocking cpuset.mems setting option
config: sparc64-randconfig-001-20250520 (https://download.01.org/0day-ci/archive/20250520/202505202106.sXzGXeU4-lkp@intel.com/config)
compiler: sparc64-linux-gcc (GCC) 8.5.0
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20250520/202505202106.sXzGXeU4-lkp@intel.com/reproduce)

If you fix the issue in a separate patch/commit (i.e. not just a new version of
the same patch/commit), kindly add following tags
| Reported-by: kernel test robot <lkp@intel.com>
| Closes: https://lore.kernel.org/oe-kbuild-all/202505202106.sXzGXeU4-lkp@intel.com/

All errors (new ones prefixed by >>):

   kernel/cgroup/cpuset.c: In function 'cpuset_write_resmask':
>> kernel/cgroup/cpuset.c:3246:3: error: a label can only be part of a statement and a declaration is not a statement
      bool skip_migrate_once = false;
      ^~~~


vim +3246 kernel/cgroup/cpuset.c

  3215	
  3216	/*
  3217	 * Common handling for a write to a "cpus" or "mems" file.
  3218	 */
  3219	ssize_t cpuset_write_resmask(struct kernfs_open_file *of,
  3220					    char *buf, size_t nbytes, loff_t off)
  3221	{
  3222		struct cpuset *cs = css_cs(of_css(of));
  3223		struct cpuset *trialcs;
  3224		int retval = -ENODEV;
  3225	
  3226		buf = strstrip(buf);
  3227		cpus_read_lock();
  3228		mutex_lock(&cpuset_mutex);
  3229		if (!is_cpuset_online(cs))
  3230			goto out_unlock;
  3231	
  3232		trialcs = alloc_trial_cpuset(cs);
  3233		if (!trialcs) {
  3234			retval = -ENOMEM;
  3235			goto out_unlock;
  3236		}
  3237	
  3238		switch (of_cft(of)->private) {
  3239		case FILE_CPULIST:
  3240			retval = update_cpumask(cs, trialcs, buf);
  3241			break;
  3242		case FILE_EXCLUSIVE_CPULIST:
  3243			retval = update_exclusive_cpumask(cs, trialcs, buf);
  3244			break;
  3245		case FILE_MEMLIST:
> 3246			bool skip_migrate_once = false;
  3247	
  3248			if ((of->file->f_flags & O_NONBLOCK) &&
  3249				is_memory_migrate(cs) &&
  3250				!cpuset_update_flag(CS_MEMORY_MIGRATE, cs, 0))
  3251				skip_migrate_once = true;
  3252	
  3253			retval = update_nodemask(cs, trialcs, buf);
  3254	
  3255			/* Restore the migrate flag */
  3256			if (skip_migrate_once)
  3257				cpuset_update_flag(CS_MEMORY_MIGRATE, cs, 1);
  3258			break;
  3259		default:
  3260			retval = -EINVAL;
  3261			break;
  3262		}
  3263	
  3264		free_cpuset(trialcs);
  3265		if (force_sd_rebuild)
  3266			rebuild_sched_domains_locked();
  3267	out_unlock:
  3268		mutex_unlock(&cpuset_mutex);
  3269		cpus_read_unlock();
  3270		flush_workqueue(cpuset_migrate_mm_wq);
  3271		return retval ?: nbytes;
  3272	}
  3273	

-- 
0-DAY CI Kernel Test Service
https://github.com/intel/lkp-tests/wiki

Re: [PATCH] cpuset: introduce non-blocking cpuset.mems setting option

[kernel test robot]

Hi Zhongkun,

kernel test robot noticed the following build warnings:

[auto build test WARNING on tj-cgroup/for-next]
[also build test WARNING on linus/master v6.15-rc7 next-20250516]
[If your patch is applied to the wrong git tree, kindly drop us a note.
And when submitting patch, we suggest to use '--base' as documented in
https://git-scm.com/docs/git-format-patch#_base_tree_information]

url:    https://github.com/intel-lab-lkp/linux/commits/Zhongkun-He/cpuset-introduce-non-blocking-cpuset-mems-setting-option/20250520-111737
base:   https://git.kernel.org/pub/scm/linux/kernel/git/tj/cgroup.git for-next
patch link:    https://lore.kernel.org/r/20250520031552.1931598-1-hezhongkun.hzk%40bytedance.com
patch subject: [PATCH] cpuset: introduce non-blocking cpuset.mems setting option
config: s390-randconfig-002-20250520 (https://download.01.org/0day-ci/archive/20250520/202505202112.tmU9BTzA-lkp@intel.com/config)
compiler: clang version 21.0.0git (https://github.com/llvm/llvm-project f819f46284f2a79790038e1f6649172789734ae8)
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20250520/202505202112.tmU9BTzA-lkp@intel.com/reproduce)

If you fix the issue in a separate patch/commit (i.e. not just a new version of
the same patch/commit), kindly add following tags
| Reported-by: kernel test robot <lkp@intel.com>
| Closes: https://lore.kernel.org/oe-kbuild-all/202505202112.tmU9BTzA-lkp@intel.com/

All warnings (new ones prefixed by >>):

>> kernel/cgroup/cpuset.c:3246:3: warning: label followed by a declaration is a C23 extension [-Wc23-extensions]
    3246 |                 bool skip_migrate_once = false;
         |                 ^
   1 warning generated.


vim +3246 kernel/cgroup/cpuset.c

  3215	
  3216	/*
  3217	 * Common handling for a write to a "cpus" or "mems" file.
  3218	 */
  3219	ssize_t cpuset_write_resmask(struct kernfs_open_file *of,
  3220					    char *buf, size_t nbytes, loff_t off)
  3221	{
  3222		struct cpuset *cs = css_cs(of_css(of));
  3223		struct cpuset *trialcs;
  3224		int retval = -ENODEV;
  3225	
  3226		buf = strstrip(buf);
  3227		cpus_read_lock();
  3228		mutex_lock(&cpuset_mutex);
  3229		if (!is_cpuset_online(cs))
  3230			goto out_unlock;
  3231	
  3232		trialcs = alloc_trial_cpuset(cs);
  3233		if (!trialcs) {
  3234			retval = -ENOMEM;
  3235			goto out_unlock;
  3236		}
  3237	
  3238		switch (of_cft(of)->private) {
  3239		case FILE_CPULIST:
  3240			retval = update_cpumask(cs, trialcs, buf);
  3241			break;
  3242		case FILE_EXCLUSIVE_CPULIST:
  3243			retval = update_exclusive_cpumask(cs, trialcs, buf);
  3244			break;
  3245		case FILE_MEMLIST:
> 3246			bool skip_migrate_once = false;
  3247	
  3248			if ((of->file->f_flags & O_NONBLOCK) &&
  3249				is_memory_migrate(cs) &&
  3250				!cpuset_update_flag(CS_MEMORY_MIGRATE, cs, 0))
  3251				skip_migrate_once = true;
  3252	
  3253			retval = update_nodemask(cs, trialcs, buf);
  3254	
  3255			/* Restore the migrate flag */
  3256			if (skip_migrate_once)
  3257				cpuset_update_flag(CS_MEMORY_MIGRATE, cs, 1);
  3258			break;
  3259		default:
  3260			retval = -EINVAL;
  3261			break;
  3262		}
  3263	
  3264		free_cpuset(trialcs);
  3265		if (force_sd_rebuild)
  3266			rebuild_sched_domains_locked();
  3267	out_unlock:
  3268		mutex_unlock(&cpuset_mutex);
  3269		cpus_read_unlock();
  3270		flush_workqueue(cpuset_migrate_mm_wq);
  3271		return retval ?: nbytes;
  3272	}
  3273	

-- 
0-DAY CI Kernel Test Service
https://github.com/intel/lkp-tests/wiki

Re: [PATCH] cpuset: introduce non-blocking cpuset.mems setting option

[Waiman Long]

On 5/19/25 11:15 PM, Zhongkun He wrote:
> Setting the cpuset.mems in cgroup v2 can trigger memory
> migrate in cpuset. This behavior is fine for newly created
> cgroups but it can cause issues for the existing cgroups.
> In our scenario, modifying the cpuset.mems setting during
> peak times frequently leads to noticeable service latency
> or stuttering.
>
> It is important to have a consistent set of behavior for
> both cpus and memory. But it does cause issues at times,
> so we would hope to have a flexible option.
>
> This idea is from the non-blocking limit setting option in
> memory control.
>
> https://lore.kernel.org/all/20250506232833.3109790-1-shakeel.butt@linux.dev/
>
> Signed-off-by: Zhongkun He <hezhongkun.hzk@bytedance.com>
> ---
>   Documentation/admin-guide/cgroup-v2.rst |  7 +++++++
>   kernel/cgroup/cpuset.c                  | 11 +++++++++++
>   2 files changed, 18 insertions(+)
>
> diff --git a/Documentation/admin-guide/cgroup-v2.rst b/Documentation/admin-guide/cgroup-v2.rst
> index 1a16ce68a4d7..d9e8e2a770af 100644
> --- a/Documentation/admin-guide/cgroup-v2.rst
> +++ b/Documentation/admin-guide/cgroup-v2.rst
> @@ -2408,6 +2408,13 @@ Cpuset Interface Files
>   	a need to change "cpuset.mems" with active tasks, it shouldn't
>   	be done frequently.
>   
> +	If cpuset.mems is opened with O_NONBLOCK then the migration is
> +	bypassed. This is useful for admin processes that need to adjust
> +	the cpuset.mems dynamically without blocking. However, there is
> +	a risk that previously allocated pages are not within the new
> +	cpuset.mems range, which may be altered by move_pages syscall or
> +	numa_balance.
> +
>     cpuset.mems.effective
>   	A read-only multiple values file which exists on all
>   	cpuset-enabled cgroups.
> diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
> index 24b70ea3e6ce..2a0867e0c6d2 100644
> --- a/kernel/cgroup/cpuset.c
> +++ b/kernel/cgroup/cpuset.c
> @@ -3208,7 +3208,18 @@ ssize_t cpuset_write_resmask(struct kernfs_open_file *of,
>   		retval = update_exclusive_cpumask(cs, trialcs, buf);
>   		break;
>   	case FILE_MEMLIST:
> +		bool skip_migrate_once = false;
> +
> +		if ((of->file->f_flags & O_NONBLOCK) &&
> +			is_memory_migrate(cs) &&
> +			!cpuset_update_flag(CS_MEMORY_MIGRATE, cs, 0))
> +			skip_migrate_once = true;
> +
>   		retval = update_nodemask(cs, trialcs, buf);
> +
> +		/* Restore the migrate flag */
> +		if (skip_migrate_once)
> +			cpuset_update_flag(CS_MEMORY_MIGRATE, cs, 1);
>   		break;
>   	default:
>   		retval = -EINVAL;

I would prefer to temporarily make is_memory_migrate() helper return 
false by also checking an internal variable, for example, instead of 
messing with the cpuset flags.

Cheers,
Longman