[RFC, PATCH 07/12] sched/numa: skip scanning anonymous VM_UFFD_MINOR VMAs

[Kiryl Shutsemau (Meta)]

Avoid protnone conflict on anonymous VMAs. Shmem unaffected.
NUMA stats fed from uffd fault path instead.
Add NUMAB_SKIP_UFFD_MINOR trace reason.

Signed-off-by: Kiryl Shutsemau (Meta) <kas@xxxxxxxxxx>
Assisted-by: Claude:claude-opus-4-6
---
 include/linux/sched/numa_balancing.h |  1 +
 include/trace/events/sched.h         |  3 ++-
 kernel/sched/fair.c                  | 13 +++++++++++++
 3 files changed, 16 insertions(+), 1 deletion(-)

diff --git a/include/linux/sched/numa_balancing.h b/include/linux/sched/numa_balancing.h
index 52b22c5c396d..5668074a4271 100644
--- a/include/linux/sched/numa_balancing.h
+++ b/include/linux/sched/numa_balancing.h
@@ -23,6 +23,7 @@ enum numa_vmaskip_reason {
 	NUMAB_SKIP_PID_INACTIVE,
 	NUMAB_SKIP_IGNORE_PID,
 	NUMAB_SKIP_SEQ_COMPLETED,
+	NUMAB_SKIP_UFFD_MINOR,
 };
 
 #ifdef CONFIG_NUMA_BALANCING
diff --git a/include/trace/events/sched.h b/include/trace/events/sched.h
index 7b2645b50e78..02e79b56db28 100644
--- a/include/trace/events/sched.h
+++ b/include/trace/events/sched.h
@@ -728,7 +728,8 @@ DEFINE_EVENT(sched_numa_pair_template, sched_swap_numa,
 	EM( NUMAB_SKIP_SCAN_DELAY,		"scan_delay" )	\
 	EM( NUMAB_SKIP_PID_INACTIVE,		"pid_inactive" )	\
 	EM( NUMAB_SKIP_IGNORE_PID,		"ignore_pid_inactive" )		\
-	EMe(NUMAB_SKIP_SEQ_COMPLETED,		"seq_completed" )
+	EM( NUMAB_SKIP_SEQ_COMPLETED,		"seq_completed" )	\
+	EMe(NUMAB_SKIP_UFFD_MINOR,		"uffd_minor" )
 
 /* Redefine for export. */
 #undef EM
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index ab4114712be7..57beb04562cf 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -25,6 +25,7 @@
 #include <linux/hugetlb_inline.h>
 #include <linux/jiffies.h>
 #include <linux/mm_api.h>
+#include <linux/userfaultfd_k.h>
 #include <linux/highmem.h>
 #include <linux/spinlock_api.h>
 #include <linux/cpumask_api.h>
@@ -3459,6 +3460,18 @@ static void task_numa_work(struct callback_head *work)
 			continue;
 		}
 
+		/*
+		 * Skip anonymous VMAs registered for userfaultfd minor faults.
+		 * Both NUMA balancing and uffd use protnone PTEs on anonymous
+		 * memory — let uffd own the hinting. For shmem, UFFDIO_DEACTIVATE
+		 * zaps PTEs entirely (no protnone conflict), so NUMA scanning
+		 * can proceed normally.
+		 */
+		if (vma_is_anonymous(vma) && userfaultfd_minor(vma)) {
+			trace_sched_skip_vma_numa(mm, vma, NUMAB_SKIP_UFFD_MINOR);
+			continue;
+		}
+
 		/*
 		 * Shared library pages mapped by multiple processes are not
 		 * migrated as it is expected they are cache replicated. Avoid
-- 
2.51.2