[PATCH 1/6] sched/numa: Let other scheduling classes drive NUMA scanning

[Andrea Righi <arighi@nvidia.com>]

The periodic scan that installs the NUMA hinting faults is driven by
task_tick_numa(), which is reachable only from task_tick_fair(). What
the scan feeds is class independent, but a task that is not in the fair
class is never scanned, records no faults and never gets a preferred
node.

Make task_tick_numa() available to the other scheduling classes (e.g.,
sched_ext). Declare it in sched.h and move the !CONFIG_NUMA_BALANCING
stub there, so a class that has no interest in NUMA balancing keeps
costing nothing.

No functional change: task_tick_fair() remains the only caller.

Reported-by: Vladimir Vdovin <deliran@verdict.gg>
Link: https://lore.kernel.org/r/20261002124559.10367-1-deliran@verdict.gg
Signed-off-by: Andrea Righi <arighi@nvidia.com>
---
 kernel/sched/fair.c  | 6 +-----
 kernel/sched/sched.h | 5 +++++
 2 files changed, 6 insertions(+), 5 deletions(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 0e279a7768754..36df9a4dde534 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -4636,7 +4636,7 @@ void init_numa_balancing(u64 clone_flags, struct task_struct *p)
 /*
  * Drive the periodic memory faults..
  */
-static void task_tick_numa(struct rq *rq, struct task_struct *curr)
+void task_tick_numa(struct rq *rq, struct task_struct *curr)
 {
 	struct callback_head *work = &curr->numa_work;
 	u64 period, now;
@@ -4702,10 +4702,6 @@ static void update_scan_period(struct task_struct *p, int new_cpu)
 
 #else /* !CONFIG_NUMA_BALANCING: */
 
-static void task_tick_numa(struct rq *rq, struct task_struct *curr)
-{
-}
-
 static inline void account_numa_enqueue(struct rq *rq, struct task_struct *p)
 {
 }
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index 9e7993256c817..2b05c41e66e29 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -2151,6 +2151,7 @@ extern int migrate_task_to(struct task_struct *p, int cpu);
 extern int migrate_swap(struct task_struct *p, struct task_struct *t,
 			int cpu, int scpu);
 extern void init_numa_balancing(u64 clone_flags, struct task_struct *p);
+extern void task_tick_numa(struct rq *rq, struct task_struct *curr);
 
 #else /* !CONFIG_NUMA_BALANCING: */
 
@@ -2159,6 +2160,10 @@ init_numa_balancing(u64 clone_flags, struct task_struct *p)
 {
 }
 
+static inline void task_tick_numa(struct rq *rq, struct task_struct *curr)
+{
+}
+
 #endif /* !CONFIG_NUMA_BALANCING */
 
 int task_llc(const struct task_struct *p);
-- 
2.56.0