linux-kernel - [PATCH v2 5/5] mm/page_owner: update Documentation with 'show_handles' and 'show_stacks

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Message-ID: <20251001175611.575861-6-mfo@igalia.com>
Date: Wed,  1 Oct 2025 14:56:11 -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 5/5] mm/page_owner: update Documentation with 'show_handles' and 'show_stacks_handles'

Describe and provide examples for 'show_handles' and 'show_stacks_handles'.

Signed-off-by: Mauricio Faria de Oliveira <mfo@...lia.com>
---
 Documentation/mm/page_owner.rst | 32 +++++++++++++++++++++++++++++++-
 1 file changed, 31 insertions(+), 1 deletion(-)

diff --git a/Documentation/mm/page_owner.rst b/Documentation/mm/page_owner.rst
index 3a45a20fc05a..6b12f3b007ec 100644
--- a/Documentation/mm/page_owner.rst
+++ b/Documentation/mm/page_owner.rst
@@ -27,7 +27,10 @@ enabled. Other usages are more than welcome.
 It can also be used to show all the stacks and their current number of
 allocated base pages, which gives us a quick overview of where the memory
 is going without the need to screen through all the pages and match the
-allocation and free operation.
+allocation and free operation. It's also possible to show only a numeric
+identifier of all the stacks (without stack traces) and their number of
+allocated base pages (faster to read and parse, eg, for monitoring) that
+can be matched with stacks later (show_handles and show_stacks_handles).
 
 page owner is disabled by default. So, if you'd like to use it, you need
 to add "page_owner=on" to your boot cmdline. If the kernel is built
@@ -116,6 +119,33 @@ Usage
 	nr_base_pages: 20824
 	...
 
+	cat /sys/kernel/debug/page_owner_stacks/show_handles > handles_7000.txt
+	cat handles_7000.txt
+	handle: 42
+	nr_base_pages: 20824
+	...
+
+	cat /sys/kernel/debug/page_owner_stacks/show_stacks_handles > stacks_handles.txt
+	cat stacks_handles.txt
+	 post_alloc_hook+0x177/0x1a0
+	 get_page_from_freelist+0xd01/0xd80
+	 __alloc_pages+0x39e/0x7e0
+	 alloc_pages_mpol+0x22e/0x490
+	 folio_alloc+0xd5/0x110
+	 filemap_alloc_folio+0x78/0x230
+	 page_cache_ra_order+0x287/0x6f0
+	 filemap_get_pages+0x517/0x1160
+	 filemap_read+0x304/0x9f0
+	 xfs_file_buffered_read+0xe6/0x1d0 [xfs]
+	 xfs_file_read_iter+0x1f0/0x380 [xfs]
+	 __kernel_read+0x3b9/0x730
+	 kernel_read_file+0x309/0x4d0
+	 __do_sys_finit_module+0x381/0x730
+	 do_syscall_64+0x8d/0x150
+	 entry_SYSCALL_64_after_hwframe+0x62/0x6a
+	handle: 42
+	...
+
 	cat /sys/kernel/debug/page_owner > page_owner_full.txt
 	./page_owner_sort page_owner_full.txt sorted_page_owner.txt
 
-- 
2.48.1