[PATCH v2] mm/page_owner: warn when stack trace depth hits PAGE_OWNER_STACK_DEPTH limit

[Jiayuan Liang <ljykernel@163.com>]

page_owner silently truncates stack traces deeper than
PAGE_OWNER_STACK_DEPTH (16), which hides root caller information during
memory debugging.

Add a ratelimited warning to notify developers when this truncation occurs.

Signed-off-by: Jiayuan Liang <ljykernel@163.com>
---
 mm/page_owner.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/mm/page_owner.c b/mm/page_owner.c
index 8178e0be5..962a4f694 100644
--- a/mm/page_owner.c
+++ b/mm/page_owner.c
@@ -163,6 +163,9 @@ static noinline depot_stack_handle_t save_stack(gfp_t flags)
 
 	set_current_in_page_owner();
 	nr_entries = stack_trace_save(entries, ARRAY_SIZE(entries), 2);
+	if (nr_entries >= PAGE_OWNER_STACK_DEPTH)
+		pr_warn_ratelimited("page_owner: stack depth %u exceeds limit %u\n",
+			nr_entries, PAGE_OWNER_STACK_DEPTH);
 	handle = stack_depot_save(entries, nr_entries, flags);
 	if (!handle)
 		handle = failure_handle;
-- 
2.43.0