[PATCH v2 1/3] mm/page_owner: add filter infrastructure

[Zhen Ni <zhen.ni@easystack.cn>]

Add data structure for page_owner filtering functionality and create
debugfs directory for filter controls.

This adds:
- enum page_owner_print_mode with values for full_stack and stack_handle
- struct page_owner_filter with print_mode and nid_mask fields
- Static owner_filter instance initialized with default values
- page_owner_filter debugfs directory

The filter infrastructure will be used to add print_mode and NUMA node
filtering capabilities in subsequent commits.

Link: https://lore.kernel.org/linux-mm/20260417154638.22370-2-zhen.ni@easystack.cn/
Suggested-by: Zi Yan <ziy@nvidia.com>
Signed-off-by: Zhen Ni <zhen.ni@easystack.cn>
---

Changes in v2:
- Use enum page_owner_print_mode instead of bool 'compact' for better clarity
- Use nodemask_t instead of int 'nid' to support multi-node filtering
---
 mm/page_owner.c | 20 +++++++++++++++++++-
 1 file changed, 19 insertions(+), 1 deletion(-)

diff --git a/mm/page_owner.c b/mm/page_owner.c
index 8178e0be557f..5884d883837e 100644
--- a/mm/page_owner.c
+++ b/mm/page_owner.c
@@ -54,6 +54,21 @@ struct stack_print_ctx {
 	u8 flags;
 };
 
+enum page_owner_print_mode {
+	PAGE_OWNER_PRINT_FULL_STACK,
+	PAGE_OWNER_PRINT_STACK_HANDLE,
+};
+
+struct page_owner_filter {
+	enum page_owner_print_mode print_mode;
+	nodemask_t nid_mask;
+};
+
+static struct page_owner_filter owner_filter = {
+	.print_mode = PAGE_OWNER_PRINT_FULL_STACK,
+	.nid_mask = NODE_MASK_NONE,
+};
+
 static bool page_owner_enabled __initdata;
 DEFINE_STATIC_KEY_FALSE(page_owner_inited);
 
@@ -973,7 +988,7 @@ DEFINE_SIMPLE_ATTRIBUTE(page_owner_threshold_fops, &page_owner_threshold_get,
 
 static int __init pageowner_init(void)
 {
-	struct dentry *dir;
+	struct dentry *dir, *filter_dir;
 
 	if (!static_branch_unlikely(&page_owner_inited)) {
 		pr_info("page_owner is disabled\n");
@@ -981,6 +996,9 @@ 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);
+
 	dir = debugfs_create_dir("page_owner_stacks", NULL);
 	debugfs_create_file("show_stacks", 0400, dir,
 			    (void *)(STACK_PRINT_FLAG_STACK |
-- 
2.20.1