[PATCH 0/3] mm/page_owner: add filter infrastructure for compact mode and NUMA filtering

[Zhen Ni]

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

Problem Statement
=================

In production environments with large memory configurations (e.g., 250GB+),
collecting page_owner information often results in files ranging from
several gigabytes to over 10GB. This creates significant challenges:

1. Storage pressure on production systems
2. Difficulty transferring large files from production environments
3. Post-processing overhead with tools/mm/page_owner_sort.c

The primary contributor to file size is redundant stack trace
information. While the kernel already deduplicates stacks via
stackdepot, page_owner retrieves and stores full stack traces for
each page, only to deduplicate them again during post-processing.

Additionally, in NUMA-aware environments (e.g., DPDK-based cloud
deployments where QEMU processes are bound to specific NUMA nodes),
OOM events are often node-specific rather than system-wide.
Currently, page_owner cannot filter by NUMA node, forcing users to
collect and analyze data for all nodes.

Solution
========

This patch series introduces a flexible filter infrastructure with
two initial filters:

1. **Compact Mode Filter**: Outputs only stack handles instead of
   full stack traces. The handle-to-stack mapping can be retrieved
   from the existing show_stacks_handles interface. This dramatically
   reduces output size while preserving all allocation metadata.

2. **NUMA Node Filter**: Allows filtering pages by specific NUMA node ID,
   enabling targeted analysis of memory issues in NUMA-aware deployments.

Implementation
==============

The series is structured as follows:

- Patch 1: Add filter infrastructure (data structures and
  debugfs directory)
- Patch 2: Implement compact mode filter
- Patch 3: Implement NUMA node filter

Usage Example
=============

Enable compact mode and filter for NUMA node 2:

    # cd /sys/kernel/debug/page_owner_filter/
    # echo 1 > compact
    # echo 2 > nid
    # cat /sys/kernel/debug/page_owner > page_owner_0417.txt

Sample compact mode output:

    Page allocated via order 0, mask 0x0(), pid 0, tgid 0 (swapper),
    ts 0 ns PFN 0x80000 type Unmovable Block 1024 type Unmovable
    Flags 0x23fffe0000000000(node=2|zone=0|lastcpupid=0x1ffff)
    handle: 1048577

    Page allocated via order 0, mask 0x252000(__GFP_NOWARN|
    __GFP_NORETRY|__GFP_COMP|__GFP_THISNODE), pid 0, tgid 0 (swapper),
    ts 0 ns PFN 0x80002 type Unmovable Block 1024 type Unmovable
    Flags 0x23fffe0000000200(workingset|node=2|zone=0|lastcpupid=0x1ffff)
    handle: 1048577

Future Enhancements
==================

The filter infrastructure is designed to be extensible. Potential
future filters could include:
- PID/TGID filtering
- Time range filtering (allocation timestamp windows)
- GFP flag filtering
- Migration type filtering

Testing
=======

Tested on a system with multiple NUMA nodes. Verified that:
- Filters work independently and in combination
- Compact mode output correlates correctly with show_stacks_handles
- Default behavior (filters disabled) remains unchanged

Signed-off-by: Zhen Ni <zhen.ni@xxxxxxxxxxxx>

---

Zhen Ni (3):
  mm/page_owner: add filter infrastructure
  mm/page_owner: add compact mode filter
  mm/page_owner: add NUMA node filter

 mm/page_owner.c | 71 +++++++++++++++++++++++++++++++++++++++++++++++--
 1 file changed, 69 insertions(+), 2 deletions(-)

--
2.20.1