[PATCH 2/6] mm/page_owner: use MIGRATE_REASON_NONE instead of -1 for last_migrate_reason

[Ye Liu <ye.liu@linux.dev>]

The last_migrate_reason field uses -1 as a sentinel value to mean "no
migration has happened".  Replace the four bare -1 occurrences with a
local MIGRATE_REASON_NONE define so the intent is explicit and the
magic number is eliminated.

No functional change.

Signed-off-by: Ye Liu <ye.liu@linux.dev>
---
 mm/page_owner.c | 15 +++++++++++----
 1 file changed, 11 insertions(+), 4 deletions(-)

diff --git a/mm/page_owner.c b/mm/page_owner.c
index 342549891a8d..ebafa9d7ff07 100644
--- a/mm/page_owner.c
+++ b/mm/page_owner.c
@@ -21,6 +21,13 @@
  */
 #define PAGE_OWNER_STACK_DEPTH (16)
 
+/*
+ * Used to indicate that a page has never been migrated, as the valid
+ * migrate_reason values are non-negative enum members (MR_* in
+ * include/linux/migrate_mode.h).
+ */
+#define MIGRATE_REASON_NONE (-1)
+
 struct page_owner {
 	unsigned short order;
 	short last_migrate_reason;
@@ -339,7 +346,7 @@ noinline void __set_page_owner(struct page *page, unsigned short order,
 	depot_stack_handle_t handle;
 
 	handle = save_stack(gfp_mask);
-	__update_page_owner_handle(page, handle, order, gfp_mask, -1,
+	__update_page_owner_handle(page, handle, order, gfp_mask, MIGRATE_REASON_NONE,
 				   ts_nsec, current->pid, current->tgid,
 				   current->comm);
 	inc_stack_record_count(handle, gfp_mask, 1 << order);
@@ -596,7 +603,7 @@ print_page_owner(char __user *buf, size_t count, unsigned long pfn,
 	if (ret >= count)
 		goto err;
 
-	if (page_owner->last_migrate_reason != -1) {
+	if (page_owner->last_migrate_reason != MIGRATE_REASON_NONE) {
 		ret += scnprintf(kbuf + ret, count - ret,
 			"Page has been migrated, last migrate reason: %s\n",
 			migrate_reason_names[page_owner->last_migrate_reason]);
@@ -667,7 +674,7 @@ void __dump_page_owner(const struct page *page)
 		stack_depot_print(handle);
 	}
 
-	if (page_owner->last_migrate_reason != -1)
+	if (page_owner->last_migrate_reason != MIGRATE_REASON_NONE)
 		pr_alert("page has been migrated, last migrate reason: %s\n",
 			migrate_reason_names[page_owner->last_migrate_reason]);
 	page_ext_put(page_ext);
@@ -826,7 +833,7 @@ static void init_pages_in_zone(struct zone *zone)
 
 			/* Found early allocated page */
 			__update_page_owner_handle(page, early_handle, 0, 0,
-						   -1, local_clock(), current->pid,
+						   MIGRATE_REASON_NONE, local_clock(), current->pid,
 						   current->tgid, current->comm);
 			count++;
 ext_put_continue:
-- 
2.43.0