[PATCH v2 2/3] mm/page_owner: add print_mode filter

Zhen Ni
2026-04-19T15:56:08Z

Add print_mode functionality to reduce page_owner output size by
printing only the stack handle instead of the full stack trace.

Example output with print_mode enabled:
Page allocated via order 0, mask 0x42800(GFP_NOWAIT|__GFP_COMP),
pid 1, tgid 1 (systemd), ts 349667370 ns
PFN 0xa00a2 type Unmovable Block 1280 type Unmovable
Flags 0x33fffe0000004124(referenced|lru|active|private|node=3|zone=0|
lastcpupid=0x1ffff)
handle: 17432583
Charged to memcg /

Print mode significantly reduces output size while preserving all
other page allocation information. The correspondence between handles
and stack traces can be obtained through the show_stacks_handles interface.

Link: https://lore.kernel.org/linux-mm/20260417154638.22370-3-zhen.ni@easystack.cn/
Suggested-by: Zi Yan <ziy@nvidia.com>
Signed-off-by: Zhen Ni <zhen.ni@easystack.cn>
---

Changes in v2:
- Renamed from 'compact mode' to 'print_mode' for better clarity
- Use enum values (0=full_stack, 1=stack_handle) instead of boolean
- Update debugfs filename from 'compact' to 'print_mode'
---
mm/page_owner.c | 28 +++++++++++++++++++++++++++-
1 file changed, 27 insertions(+), 1 deletion(-)

diff --git a/mm/page_owner.c b/mm/page_owner.c
index 5884d883837e..6d87b6948cfa 100644
--- a/mm/page_owner.c
+++ b/mm/page_owner.c
@@ -590,7 +590,13 @@ print_page_owner(char __user *buf, size_t count, unsigned long pfn,
migratetype_names[pageblock_mt],
&page->flags);

- ret += stack_depot_snprint(handle, kbuf + ret, count - ret, 0);
+ /* Print mode: full stack or stack handle */
+ if (READ_ONCE(owner_filter.print_mode) == PAGE_OWNER_PRINT_STACK_HANDLE) {
+ ret += scnprintf(kbuf + ret, count - ret,
+ "handle: %d\n", handle);
+ } else {
+ ret += stack_depot_snprint(handle, kbuf + ret, count - ret, 0);
+ }
if (ret >= count)
goto err;

@@ -985,6 +991,24 @@ static int page_owner_threshold_set(void *data, u64 val)
DEFINE_SIMPLE_ATTRIBUTE(page_owner_threshold_fops, &page_owner_threshold_get,
&page_owner_threshold_set, "%llu");

+static int page_owner_print_mode_get(void *data, u64 *val)
+{
+ *val = READ_ONCE(owner_filter.print_mode);
+ return 0;
+}
+
+static int page_owner_print_mode_set(void *data, u64 val)
+{
+ if (val > PAGE_OWNER_PRINT_STACK_HANDLE)
+ return -EINVAL;
+ WRITE_ONCE(owner_filter.print_mode, val);
+ return 0;
+}
+
+DEFINE_SIMPLE_ATTRIBUTE(page_owner_print_mode_fops,
+ &page_owner_print_mode_get,
+ &page_owner_print_mode_set, "%lld");
+

static int __init pageowner_init(void)
{
@@ -998,6 +1022,8 @@ static int __init pageowner_init(void)
debugfs_create_file("page_owner", 0400, NULL, NULL, &page_owner_fops);

filter_dir = debugfs_create_dir("page_owner_filter", NULL);
+ debugfs_create_file("print_mode", 0600, filter_dir, NULL,
+ &page_owner_print_mode_fops);

dir = debugfs_create_dir("page_owner_stacks", NULL);
debugfs_create_file("show_stacks", 0400, dir,
--
2.20.1