Re: [PATCH v3 4/4] mm/page_owner: document page_owner filter features

[SeongJae Park]

On Tue, 28 Apr 2026 15:11:12 +0800 Zhen Ni <zhen.ni@xxxxxxxxxxxx> wrote:

> Add documentation for the page_owner filter functionality, including:
> - Print mode filter (full stack vs stack handle)
> - NUMA node filter (single node, multiple nodes, ranges)
> - Usage examples for both filters
> 
> Signed-off-by: Zhen Ni <zhen.ni@xxxxxxxxxxxx>
> ---
> 
> Changes in v3:
> - New patch to document filter features as requested by Andrew Morton
> ---
>  Documentation/mm/page_owner.rst | 55 ++++++++++++++++++++++++++++++++-
>  1 file changed, 54 insertions(+), 1 deletion(-)
> 
> diff --git a/Documentation/mm/page_owner.rst b/Documentation/mm/page_owner.rst
> index 6b12f3b007ec..6261366d33fe 100644
> --- a/Documentation/mm/page_owner.rst
> +++ b/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

Nit.  Other parts of the document uses tab for the indentation, while the above
new snippet is using four spaces.  How about using tab for the consistency?

> +
> +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

Tab for indentation?

> +
> +To retrieve the full stack trace for a handle, use::
> +
> +    cat /sys/kernel/debug/page_owner_stacks/show_stacks_handles

Tab?

> +
> +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
>  ==========================
>  ::
> -- 
> 2.20.1


Thanks,
SJ