linux-kernel - [PATCH v2 4/5] mm/page_owner: add debugfs file 'show_stacks

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Message-ID: <20251001175611.575861-5-mfo@igalia.com>
Date: Wed,  1 Oct 2025 14:56:10 -0300
From: Mauricio Faria de Oliveira <mfo@...lia.com>
To: Michal Hocko <mhocko@...e.com>,
	Vlastimil Babka <vbabka@...e.cz>,
	Andrew Morton <akpm@...ux-foundation.org>
Cc: Oscar Salvador <osalvador@...e.de>,
	Suren Baghdasaryan <surenb@...gle.com>,
	Brendan Jackman <jackmanb@...gle.com>,
	Johannes Weiner <hannes@...xchg.org>,
	Zi Yan <ziy@...dia.com>,
	linux-mm@...ck.org,
	linux-kernel@...r.kernel.org,
	kernel-dev@...lia.com
Subject: [PATCH v2 4/5] mm/page_owner: add debugfs file 'show_stacks_handles'

Add the file 'show_stacks_handles' to show just stack traces and their
handles, in order to resolve stack traces and handles (i.e., to identify
the stack traces for handles in previous reads from 'show_handles').

All stacks/handles must show up, regardless of their number of pages, that
might have become zero or no longer make 'count_threshold', but made it in
previous reads from 'show_handles' -- and need to be resolved later.

P.S.: now, print the extra newline independently of the number of pages.

Signed-off-by: Mauricio Faria de Oliveira <mfo@...lia.com>
---
 mm/page_owner.c | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/mm/page_owner.c b/mm/page_owner.c
index 5d488fce0e3d..0e5c7bb3e4e8 100644
--- a/mm/page_owner.c
+++ b/mm/page_owner.c
@@ -913,7 +913,8 @@ static int stack_print(struct seq_file *m, void *v)
 
 	nr_base_pages = refcount_read(&stack_record->count) - 1;
 
-	if (nr_base_pages < 1 || nr_base_pages < page_owner_pages_threshold)
+	if (ctx->flags & STACK_PRINT_FLAG_PAGES &&
+	    (nr_base_pages < 1 || nr_base_pages < page_owner_pages_threshold))
 		return 0;
 
 	if (ctx->flags & STACK_PRINT_FLAG_STACK) {
@@ -925,7 +926,8 @@ static int stack_print(struct seq_file *m, void *v)
 	if (ctx->flags & STACK_PRINT_FLAG_HANDLE)
 		seq_printf(m, "handle: %d\n", stack_record->handle.handle);
 	if (ctx->flags & STACK_PRINT_FLAG_PAGES)
-		seq_printf(m, "nr_base_pages: %d\n\n", nr_base_pages);
+		seq_printf(m, "nr_base_pages: %d\n", nr_base_pages);
+	seq_putc(m, '\n');
 
 	return 0;
 }
@@ -999,6 +1001,10 @@ static int __init pageowner_init(void)
 			    (void *)(STACK_PRINT_FLAG_HANDLE |
 				     STACK_PRINT_FLAG_PAGES),
 			    &page_owner_stack_operations);
+	debugfs_create_file("show_stacks_handles", 0400, dir,
+			    (void *)(STACK_PRINT_FLAG_STACK |
+				     STACK_PRINT_FLAG_HANDLE),
+			    &page_owner_stack_operations);
 	debugfs_create_file("count_threshold", 0600, dir, NULL,
 			    &proc_page_owner_threshold);
 
-- 
2.48.1