Re: [PATCH v3 0/4] mm/page_owner: add filter infrastructure for print_mode and NUMA filtering

[Andrew Morton]

On Tue, 28 Apr 2026 15:11:08 +0800 Zhen Ni <zhen.ni@xxxxxxxxxxxx> wrote:

> This patch series introduces filtering capabilities to the page_owner
> feature to address storage and performance challenges in production
> environments.

Thanks, I updated mm.git's mm-new branch to this version.

> Changes from v2:
> - Remove READ_ONCE/WRITE_ONCE for nodemask_t (fixes compilation errors)
>   * nodemask_t is a large structure (128 bytes) that triggers compile-time asserts
>   * Direct assignment is safe for this use case
> - Add comment explaining input length calculation formula
>   * 6 bytes = ",NNNNN" (comma + 5-digit node number)
> - Simplify "-1" check using kstrtoint() instead of dual strcmp()
> - Move nodemask_t mask read outside PFN iteration loop for performance
>   * Avoids 128-byte structure copy on each iteration
> - Add documentation for filter features (patch 4/4)

Here's how v3 altered mm.git:



 Documentation/mm/page_owner.rst |   55 +++++++++++++++++++++++++++++-
 mm/page_owner.c                 |   14 +++++--
 2 files changed, 64 insertions(+), 5 deletions(-)

--- a/Documentation/mm/page_owner.rst~b
+++ a/Documentation/mm/page_owner.rst
@@ -74,7 +74,17 @@ Usage
 
 3) Do the job that you want to debug.
 
-4) Analyze information from page owner::
+4) (Optional) Use filters to focus on specific memory allocations::
+
+    cd /sys/kernel/debug/page_owner_filter
+
+    # Print only stack handles instead of full traces
+    echo 1 > print_mode
+
+    # Filter by NUMA nodes
+    echo "0,2-3" > nid
+
+5) Analyze information from page owner::
 
 	cat /sys/kernel/debug/page_owner_stacks/show_stacks > stacks.txt
 	cat stacks.txt
@@ -238,6 +248,49 @@ Usage
 				./page_owner_sort <input> <output> --tgid=1,2,3
 				./page_owner_sort <input> <output> --name name1,name2
 
+Page Owner Filters
+==================
+
+The page_owner feature provides filtering capabilities to focus on specific
+memory allocations (e.g., by NUMA node). Filters are controlled through debugfs
+files in ``/sys/kernel/debug/page_owner_filter/``.
+
+Print Mode Filter
+-----------------
+
+The ``print_mode`` file controls the level of detail in stack trace output.
+
+Available modes:
+
+- ``0`` (default): Print full stack traces
+- ``1``: Print only stack handles
+
+The ``print_mode=1`` output format::
+
+    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(...)
+    handle: 17432583
+
+To retrieve the full stack trace for a handle, use::
+
+    cat /sys/kernel/debug/page_owner_stacks/show_stacks_handles
+
+NUMA Node Filter
+----------------
+
+The ``nid`` file filters pages by NUMA node. This is useful for NUMA-aware
+environments to analyze node-specific memory allocation.
+
+Supported input formats:
+
+- Single node: ``echo "2" > nid``
+- Multiple nodes: ``echo "0,2,3" > nid``
+- Node range: ``echo "0-3" > nid``
+- Mixed format: ``echo "0,2-4,7" > nid``
+- Disable filter: ``echo "-1" > nid``
+
 STANDARD FORMAT SPECIFIERS
 ==========================
 ::
--- a/mm/page_owner.c~b
+++ a/mm/page_owner.c
@@ -685,6 +685,7 @@ read_page_owner(struct file *file, char
 	struct page_ext *page_ext;
 	struct page_owner *page_owner;
 	depot_stack_handle_t handle;
+	nodemask_t mask;
 
 	if (!static_branch_unlikely(&page_owner_inited))
 		return -EINVAL;
@@ -698,6 +699,8 @@ read_page_owner(struct file *file, char
 	while (!pfn_valid(pfn) && (pfn & (MAX_ORDER_NR_PAGES - 1)) != 0)
 		pfn++;
 
+	mask = owner_filter.nid_mask;
+
 	/* Find an allocated page */
 	for (; pfn < max_pfn; pfn++) {
 		/*
@@ -707,7 +710,6 @@ read_page_owner(struct file *file, char
 		 * user through copy_to_user() or GFP_KERNEL allocations.
 		 */
 		struct page_owner page_owner_tmp;
-		nodemask_t mask;
 
 		/*
 		 * If the new page is in a new MAX_ORDER_NR_PAGES area,
@@ -732,7 +734,6 @@ read_page_owner(struct file *file, char
 			continue;
 
 		/* NUMA node filter using bitmask */
-		mask = owner_filter.nid_mask;
 		if (!nodes_empty(mask)) {
 			int nid = page_to_nid(page);
 
@@ -1026,8 +1027,13 @@ static ssize_t nid_filter_write(struct f
 	char *kbuf;
 	nodemask_t mask;
 	int ret;
+	int val;
 
-	/* Limit input size to handle worst-case nodelist (all nodes) */
+	/*
+	 * Limit input size to handle worst-case nodelist (all nodes).
+	 * Worst case per node: ",NNNNN" (comma + 5-digit node number) = 6 bytes.
+	 * Formula: 100 bytes overhead + 6 * MAX_NUMNODES
+	 */
 	if (count > (100 + 6 * MAX_NUMNODES))
 		return -EINVAL;
 
@@ -1042,7 +1048,7 @@ static ssize_t nid_filter_write(struct f
 	kbuf[count] = '\0';
 
 	/* Support: "-1" to clear, or nodelist format like "0", "0,2", "0-3" */
-	if (strcmp(kbuf, "-1\n") == 0 || strcmp(kbuf, "-1") == 0)
+	if (kstrtoint(kbuf, 10, &val) == 0 && val == -1)
 		nodes_clear(mask);
 	else if (nodelist_parse(kbuf, mask)) {
 		ret = -EINVAL;
_