[PATCH v4 2/7] mm/page_owner: add MR_NEVER to enum migrate_reason and use it 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 by
adding a proper MR_NEVER member to enum migrate_reason, defining a
corresponding "never_migrated" string in the MIGRATE_REASON trace
macro, and updating the GDB page_owner script to use MR_NEVER instead
of the hardcoded -1 so that lx-dump-page-owner does not incorrectly
report unmigrated pages as migrated.

No functional change.

Signed-off-by: Ye Liu <ye.liu@linux.dev>
Reviewed-by: Zi Yan <ziy@nvidia.com>
Reviewed-by: Vlastimil Babka (SUSE) <vbabka@kernel.org>
---
 include/linux/migrate_mode.h    | 1 +
 include/trace/events/migrate.h  | 3 ++-
 mm/page_owner.c                 | 8 ++++----
 scripts/gdb/linux/page_owner.py | 4 +++-
 4 files changed, 10 insertions(+), 6 deletions(-)

diff --git a/include/linux/migrate_mode.h b/include/linux/migrate_mode.h
index 265c4328b36a..05102d4d2490 100644
--- a/include/linux/migrate_mode.h
+++ b/include/linux/migrate_mode.h
@@ -25,6 +25,7 @@ enum migrate_reason {
 	MR_LONGTERM_PIN,
 	MR_DEMOTION,
 	MR_DAMON,
+	MR_NEVER,		/* page has never been migrated */
 	MR_TYPES
 };
 
diff --git a/include/trace/events/migrate.h b/include/trace/events/migrate.h
index cd01dd7b3640..11bc0aa14c7e 100644
--- a/include/trace/events/migrate.h
+++ b/include/trace/events/migrate.h
@@ -23,7 +23,8 @@
 	EM( MR_CONTIG_RANGE,	"contig_range")			\
 	EM( MR_LONGTERM_PIN,	"longterm_pin")			\
 	EM( MR_DEMOTION,	"demotion")			\
-	EMe(MR_DAMON,		"damon")
+	EM( MR_DAMON,		"damon")			\
+	EMe(MR_NEVER,		"never_migrated")
 
 /*
  * First define the enums in the above macros to be exported to userspace
diff --git a/mm/page_owner.c b/mm/page_owner.c
index 342549891a8d..c2f43ab860eb 100644
--- a/mm/page_owner.c
+++ b/mm/page_owner.c
@@ -339,7 +339,7 @@ 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, MR_NEVER,
 				   ts_nsec, current->pid, current->tgid,
 				   current->comm);
 	inc_stack_record_count(handle, gfp_mask, 1 << order);
@@ -596,7 +596,7 @@ 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 != MR_NEVER) {
 		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 +667,7 @@ 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 != MR_NEVER)
 		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 +826,7 @@ 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,
+						   MR_NEVER, local_clock(), current->pid,
 						   current->tgid, current->comm);
 			count++;
 ext_put_continue:
diff --git a/scripts/gdb/linux/page_owner.py b/scripts/gdb/linux/page_owner.py
index 8e713a09cfe7..eeabaeed438b 100644
--- a/scripts/gdb/linux/page_owner.py
+++ b/scripts/gdb/linux/page_owner.py
@@ -34,6 +34,7 @@ class DumpPageOwner(gdb.Command):
     max_pfn = None
     p_ops = None
     migrate_reason_names = None
+    mr_never = None
 
     def __init__(self):
         super(DumpPageOwner, self).__init__("lx-dump-page-owner", gdb.COMMAND_SUPPORT)
@@ -65,6 +66,7 @@ class DumpPageOwner(gdb.Command):
         self.max_pfn = int(gdb.parse_and_eval("max_pfn"))
         self.page_ext_size = int(gdb.parse_and_eval("page_ext_size"))
         self.migrate_reason_names = gdb.parse_and_eval('migrate_reason_names')
+        self.mr_never = int(gdb.parse_and_eval('MR_NEVER'))
 
     def page_ext_invalid(self, page_ext):
         if page_ext == gdb.Value(0):
@@ -138,7 +140,7 @@ class DumpPageOwner(gdb.Command):
         else:
             gdb.write('page last free stack trace:\n')
             stackdepot.stack_depot_print(page_owner["free_handle"])
-        if page_owner['last_migrate_reason'] != -1:
+        if page_owner['last_migrate_reason'] != self.mr_never:
             gdb.write('page has been migrated, last migrate reason: %s\n' % self.migrate_reason_names[page_owner['last_migrate_reason']])
 
     def read_page_owner(self):
-- 
2.43.0