[PATCH] sched/numa, mm: Skip page promotion if cpu pid is valid

[Donet Tom <donettom@linux.ibm.com>]

If memory tiering is disabled, cpupid of slow memory pages may
contain a valid CPU and PID. If tiering is enabled at runtime,
there is a chance that in should_numa_migrate_memory(), this
valid CPU/PID is treated as a last access timestamp, leading
to unnecessary promotion.

Prevent this by skipping promotion when cpupid is valid.

Signed-off-by: Donet Tom <donettom@linux.ibm.com>
---
 kernel/sched/fair.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 4b43809a3fb1..f5830a5a94d5 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -2001,6 +2001,13 @@ bool should_numa_migrate_memory(struct task_struct *p, struct folio *folio,
 		unsigned int latency, th, def_th;
 		long nr = folio_nr_pages(folio);
 
+		/* When tiering is enabled at runtime, last_cpupid may
+		 * hold a valid cpupid instead of an access timestamp.
+		 * If so, skip page promotion.
+		 */
+		if (cpupid_valid(folio_last_cpupid(folio)))
+			return false;
+
 		pgdat = NODE_DATA(dst_nid);
 		if (pgdat_free_space_enough(pgdat)) {
 			/* workload changed, reset hot threshold */
-- 
2.47.1