From e2c75342c24f7420e4011a6745ba0f85c4fc047d Mon Sep 17 00:00:00 2001 From: Zhen Ni Date: Tue, 7 Jul 2026 19:54:11 +0800 Subject: [PATCH] mm/page_owner: document page_owner filter Add documentation for the page_owner_filter userspace tool and kernel-level filtering features. [rdunlap@infradead.org: avoid docs build warning] Link: https://lore.kernel.org/20260708213548.469155-1-rdunlap@infradead.org Link: https://lore.kernel.org/20260707115411.1714314-5-zhen.ni@easystack.cn Signed-off-by: Zhen Ni Signed-off-by: Randy Dunlap Acked-by: Vlastimil Babka (SUSE) Acked-by: Zi Yan Cc: Brendan Jackman Cc: Johannes Weiner Cc: Michal Hocko Cc: Suren Baghdasaryan Signed-off-by: Andrew Morton --- Documentation/mm/page_owner.rst | 78 ++++++++++++++++++++++++++++++++- 1 file changed, 76 insertions(+), 2 deletions(-) diff --git a/Documentation/mm/page_owner.rst b/Documentation/mm/page_owner.rst index 6b12f3b007ec..a6bd3fe6423a 100644 --- a/Documentation/mm/page_owner.rst +++ b/Documentation/mm/page_owner.rst @@ -65,7 +65,15 @@ un-tracking state. Usage ===== -1) Build user-space helper:: +1) Build user-space helpers: +:: + + To filter page_owner output: + + cd tools/mm + make page_owner_filter + + To sort and analyze page_owner output: cd tools/mm make page_owner_sort @@ -74,7 +82,11 @@ Usage 3) Do the job that you want to debug. -4) Analyze information from page owner:: +4) (Optional) Filter page_owner output:: + + ./page_owner_filter -m handle -n 0,1,2 > filtered_page_owner.txt + +5) Analyze information from page owner:: cat /sys/kernel/debug/page_owner_stacks/show_stacks > stacks.txt cat stacks.txt @@ -263,3 +275,65 @@ STANDARD FORMAT SPECIFIERS f free whether the page has been released or not st stacktrace stack trace of the page allocation ator allocator memory allocator for pages + +Filtering page_owner output +============================ + +page_owner supports filtering output at the kernel level before reading, +which reduces the amount of data that needs to be processed in userspace. + +The page_owner_filter tool provides a convenient interface for this filtering +capability. It supports two types of filters: + +1. **print_mode filter**: Control what information is printed for each page + - ``stack``: Print full stack traces (default, compatible with existing usage) + - ``handle``: Print only stack handle numbers (much faster, smaller output) + - ``stack_handle``: Print both stack traces and handle numbers + + The ``handle`` mode uses numeric identifiers instead of full stack traces. + The mapping from handles to actual stack traces can be obtained via the + show_stacks_handles interface. + +2. **NUMA node filter**: Filter pages by NUMA node ID + - Supports single node: ``-n 0`` + - Multiple nodes: ``-n 0,1,2`` + - Ranges: ``-n 0-3`` + - Mixed format: ``-n 0,2-3,5`` + +Usage examples:: + + # Filter by print mode + ./page_owner_filter -m handle + ./page_owner_filter -m stack_handle + + # Filter by NUMA node + ./page_owner_filter -n 0 + ./page_owner_filter -n 0-3 + + # Combined filters + ./page_owner_filter -m stack -n 0,1,2 + ./page_owner_filter -m handle -n 0,2-3 + + # Save to file + ./page_owner_filter -m handle -o filtered_output.txt + +The handle mode is particularly useful for monitoring and performance-critical +scenarios as it dramatically reduces output size. Testing shows handle mode can +reduce output size by ~66% (84MB vs 244MB) and improve read performance by ~4.4x +compared to full stack output. + +The NUMA node filter is useful for NUMA-aware memory allocation analysis and debugging. + +Behind the scenes, page_owner_filter opens /sys/kernel/debug/page_owner and +writes filter commands before reading the filtered output. The filtering uses +per-file-descriptor state, allowing each open() to have independent filter settings. + +Each file descriptor maintains its own filter state, so you can have multiple +independent filtering operations running concurrently. For example, in different +terminals you can run different filters simultaneously:: + + # Terminal 1: Filter node 0 + ./page_owner_filter -n 0 > node0_output.txt + + # Terminal 2: Filter node 1 (runs concurrently) + ./page_owner_filter -n 1 > node1_output.txt