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

Andrew Morton
2026-04-28T14:15:48Z

On Tue, 28 Apr 2026 15:11:08 +0800 Zhen Ni <zhen.ni@easystack.cn> 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 --tgid=1,2,3
./page_owner_sort --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;
_