Re: [PATCH v3] sched/numa: add statistics of numa balance task migration

From: Chen, Yu C
Date: Fri May 02 2025 - 05:31:18 EST

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In reply to: Libo Chen: "Re: [PATCH v3] sched/numa: add statistics of numa balance task migration"
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Hi Libo,

On 5/1/2025 3:00 PM, Libo Chen wrote:

Hi Chen Yu

On 4/30/25 03:36, Chen Yu wrote:

On systems with NUMA balancing enabled, it is found that tracking
the task activities due to NUMA balancing is helpful. NUMA balancing
has two mechanisms for task migration: one is to migrate the task to
an idle CPU in its preferred node, the other is to swap tasks on
different nodes if they are on each other's preferred node.

The kernel already has NUMA page migration statistics in
/sys/fs/cgroup/mytest/memory.stat and /proc/{PID}/sched,
but does not have statistics for task migration/swap.
Add the task migration and swap count accordingly.

The following two new fields:

numa_task_migrated
numa_task_swapped

will be displayed in both
/sys/fs/cgroup/{GROUP}/memory.stat and /proc/{PID}/sched

Both stats show up in expected places, but I notice they are also in
/proc/vmstat and are always 0.

I think you may have to add count_vm_numa_event() in migrate_task_to()
and __migrate_swap_task() unless there is a way to not show both stats
in /proc/vmstat.

Thanks for catching this. For some reasons, I added these
"placeholders" to the vmstat but didn't populate them. Let
me remove these items from vmstat because we mainly care
about task activity rather than page activity(not a vm event
I suppose) Let me have a try on this.

Introducing both pertask and permemcg NUMA balancing statistics helps
to quickly evaluate the performance and resource usage of the target
workload. For example, the user can first identify the container which
has high NUMA balance activity and then narrow down to a specific task
within that group, and tune the memory policy of that task.
In summary, it is plausible to iterate the /proc/$pid/sched to find the
offending task, but the introduction of per memcg tasks' Numa balancing
aggregated activity can further help users identify the task in a
divide-and-conquer way.

Tested-by: K Prateek Nayak <kprateek.nayak@xxxxxxx>
Tested-by: Madadi Vineeth Reddy <vineethr@xxxxxxxxxxxxx>
Acked-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Signed-off-by: Chen Yu <yu.c.chen@xxxxxxxxx>
---
v2->v3:
Remove unnecessary p->mm check because kernel threads are
not supported by Numa Balancing. (Libo Chen)
v1->v2:
Update the Documentation/admin-guide/cgroup-v2.rst. (Michal)
---
Documentation/admin-guide/cgroup-v2.rst | 6 ++++++
include/linux/sched.h | 4 ++++
include/linux/vm_event_item.h | 2 ++
kernel/sched/core.c | 7 +++++--
kernel/sched/debug.c | 4 ++++
mm/memcontrol.c | 2 ++
mm/vmstat.c | 2 ++
7 files changed, 25 insertions(+), 2 deletions(-)

diff --git a/Documentation/admin-guide/cgroup-v2.rst b/Documentation/admin-guide/cgroup-v2.rst
index 1a16ce68a4d7..d346f3235945 100644
--- a/Documentation/admin-guide/cgroup-v2.rst
+++ b/Documentation/admin-guide/cgroup-v2.rst
@@ -1670,6 +1670,12 @@ The following nested keys are defined.
numa_hint_faults (npn)
Number of NUMA hinting faults.
+ numa_task_migrated (npn)
+ Number of task migration by NUMA balancing.
+
+ numa_task_swapped (npn)
+ Number of task swap by NUMA balancing.
+
pgdemote_kswapd
Number of pages demoted by kswapd.
diff --git a/include/linux/sched.h b/include/linux/sched.h
index f96ac1982893..1c50e30b5c01 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -549,6 +549,10 @@ struct sched_statistics {
u64 nr_failed_migrations_running;
u64 nr_failed_migrations_hot;
u64 nr_forced_migrations;
+#ifdef CONFIG_NUMA_BALANCING
+ u64 numa_task_migrated;
+ u64 numa_task_swapped;
+#endif

This one is more of personal preference. I understand they show up only if
you turn on schedstats, but will it be better to put them in sched_show_numa()
so they will be printed out next to other numa stats such as numa_pages_migrated?

@@ -1153,6 +1153,10 @@ static void sched_show_numa(struct task_struct *p, struct seq_file *m)
if (p->mm)
P(mm->numa_scan_seq);

+ if (schedstat_enabled()) {
+ P_SCHEDSTAT(numa_task_migrated);
+ P_SCHEDSTAT(numa_task_swapped);
+ }
P(numa_pages_migrated);
P(numa_preferred_nid);
P(total_numa_faults);

Previously, the numa_task_migrated and numa_task_swapped were
put under the scope of schedstat_enabled() in
proc_sched_show_task().

We mainly care about task migration activity, so it is put near
the nr_forced_migrations. When it reaches sched_show_numa(),
P_SCHEDSTAT has been undefined. It is just simpler to do this
directly in proc_sched_show_task() IMO.

Thanks,
Chenyu

Thanks,
Libo

u64 nr_wakeups;
u64 nr_wakeups_sync;
diff --git a/include/linux/vm_event_item.h b/include/linux/vm_event_item.h
index 9e15a088ba38..91a3ce9a2687 100644
--- a/include/linux/vm_event_item.h
+++ b/include/linux/vm_event_item.h
@@ -66,6 +66,8 @@ enum vm_event_item { PGPGIN, PGPGOUT, PSWPIN, PSWPOUT,
NUMA_HINT_FAULTS,
NUMA_HINT_FAULTS_LOCAL,
NUMA_PAGE_MIGRATE,
+ NUMA_TASK_MIGRATE,
+ NUMA_TASK_SWAP,
#endif
#ifdef CONFIG_MIGRATION
PGMIGRATE_SUCCESS, PGMIGRATE_FAIL,
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index c81cf642dba0..25a92f2abda4 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -3352,6 +3352,9 @@ void set_task_cpu(struct task_struct *p, unsigned int new_cpu)
#ifdef CONFIG_NUMA_BALANCING
static void __migrate_swap_task(struct task_struct *p, int cpu)
{
+ __schedstat_inc(p->stats.numa_task_swapped);
+ count_memcg_events_mm(p->mm, NUMA_TASK_SWAP, 1);
+
if (task_on_rq_queued(p)) {
struct rq *src_rq, *dst_rq;
struct rq_flags srf, drf;
@@ -7953,8 +7956,8 @@ int migrate_task_to(struct task_struct *p, int target_cpu)
if (!cpumask_test_cpu(target_cpu, p->cpus_ptr))
return -EINVAL;
- /* TODO: This is not properly updating schedstats */
-
+ __schedstat_inc(p->stats.numa_task_migrated);
+ count_memcg_events_mm(p->mm, NUMA_TASK_MIGRATE, 1);
trace_sched_move_numa(p, curr_cpu, target_cpu);
return stop_one_cpu(curr_cpu, migration_cpu_stop, &arg);
}
diff --git a/kernel/sched/debug.c b/kernel/sched/debug.c
index 56ae54e0ce6a..f971c2af7912 100644
--- a/kernel/sched/debug.c
+++ b/kernel/sched/debug.c
@@ -1206,6 +1206,10 @@ void proc_sched_show_task(struct task_struct *p, struct pid_namespace *ns,
P_SCHEDSTAT(nr_failed_migrations_running);
P_SCHEDSTAT(nr_failed_migrations_hot);
P_SCHEDSTAT(nr_forced_migrations);
+#ifdef CONFIG_NUMA_BALANCING
+ P_SCHEDSTAT(numa_task_migrated);
+ P_SCHEDSTAT(numa_task_swapped);
+#endif
P_SCHEDSTAT(nr_wakeups);
P_SCHEDSTAT(nr_wakeups_sync);
P_SCHEDSTAT(nr_wakeups_migrate);
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index c96c1f2b9cf5..cdaab8a957f3 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -463,6 +463,8 @@ static const unsigned int memcg_vm_event_stat[] = {
NUMA_PAGE_MIGRATE,
NUMA_PTE_UPDATES,
NUMA_HINT_FAULTS,
+ NUMA_TASK_MIGRATE,
+ NUMA_TASK_SWAP,
#endif
};
diff --git a/mm/vmstat.c b/mm/vmstat.c
index 4c268ce39ff2..ed08bb384ae4 100644
--- a/mm/vmstat.c
+++ b/mm/vmstat.c
@@ -1347,6 +1347,8 @@ const char * const vmstat_text[] = {
"numa_hint_faults",
"numa_hint_faults_local",
"numa_pages_migrated",
+ "numa_task_migrated",
+ "numa_task_swapped",
#endif
#ifdef CONFIG_MIGRATION
"pgmigrate_success",

Next message: Ignacio Moreno Gonzalez via B4 Relay: "[PATCH] mm: mmap: map MAP_STACK to VM_NOHUGEPAGE only if THP is enabled"
Previous message: Lad, Prabhakar: "Re: [PATCH v9 2/2] i2c: riic: Recover from arbitration loss"
In reply to: Libo Chen: "Re: [PATCH v3] sched/numa: add statistics of numa balance task migration"
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