Re: [PATCH v11 1/4] mm/page_owner: add print_mode filter

[Zi Yan]

On Thu Jun 25, 2026 at 12:30 AM EDT, Zhen Ni wrote:
> Add a print_mode filter to page_owner that allows users to choose between
> printing stack traces, stack handles, or both, providing flexibility for
> different debugging and analysis scenarios.
>
> The filter provides three modes via page_owner:
> - Writing "mode=stack" prints stack traces for each page (default)
> - Writing "mode=handle" prints only the handle number
> - Writing "mode=stack_handle" prints both stack traces and handles
>
> The default stack mode maintains backward compatibility with existing
> usage, displaying complete stack traces for each page allocation.
>
> The handle mode dramatically reduces log size and improves performance by
> showing only the handle number instead of the full stack trace. Testing
> shows handle mode reduces output size by ~66% (84MB vs 244MB) and
> improves read performance by ~4.4x compared to full stack output. The
> mapping from handles to actual stack traces can be obtained via the
> show_stacks_handles interface.
>
> The stack_handle mode prints both stack traces and handles, making it
> easier to identify pages with the same allocation pattern by comparing
> handle numbers instead of comparing large stack traces.
>
> Example usage:
>   # Using the page_owner_filter tool (recommended)
>   ./page_owner_filter -m stack          # Print only stack traces (default)
>   ./page_owner_filter -m handle         # Print only handles
>   ./page_owner_filter -m stack_handle   # Print both stack and handles
>
> Sample output (handle mode):
>   Page allocated via order 0, migratetype Unmovable, gfp_mask 0x1100ca,
>   pid 1, tgid 1 (systemd), ts 123456789 ns
>   PFN 0x1000 type Unmovable Block 1 type Unmovable
>   Flags 0x3fffe800000084(referenced|lru|active|private|node=0|zone=1)
>   handle: 17432583
>   ...
>
> This implementation uses per-file-descriptor filter state stored in
> file->private_data, allowing each opener to have independent filter
> configuration.
>
> Signed-off-by: Zhen Ni <zhen.ni@xxxxxxxxxxxx>
> ---
> Changes in v11:
> - No changes
>
> Changes in v10:
> - No changes
>
> Changes in v9:
> - Add spinlock_t lock to struct page_owner_filter_state for concurrent access protection
>
> Changes in v8:
> - Fix buffer overflow by adding bounds check between stack_depot_snprint() and scnprintf()
> - Fix unsafe string handling: use memdup_user_nul() instead of kmalloc_objs + strncpy_from_user()
> - Fix strsep() memory corruption by saving original pointer before strsep() call
> - Change format specifier from %d to %u for depot_stack_handle_t
>
> Changes in v7:
> - per-file-descriptor implementation
>
> Changes in v6:
> - Remove unnecessary braces in if/else statement (coding style)
> - Use stack array (char kbuf[33]) instead of kmalloc for input buffer
>
> Changes in v5:
> - No code changes
>
> Changes in v4:
> - Change from numeric (0/1) to string-based interface ("full_stack"/"stack_handle")
> - Merge infrastructure patch into this patch
>
> Changes in v3:
> - No code changes
>
> Changes in v2:
> - Renamed from 'compact mode' to 'print_mode' for better clarity
> - Use enum values (0=full_stack, 1=stack_handle) instead of boolean
> - Update debugfs filename from 'compact' to 'print_mode'
>
> v10: https://lore.kernel.org/linux-mm/20260618035750.3724613-2-zhen.ni@xxxxxxxxxxxx/
> v9: https://lore.kernel.org/linux-mm/20260525081652.2210206-2-zhen.ni@xxxxxxxxxxxx/
> v8: https://lore.kernel.org/linux-mm/20260520075641.1931080-2-zhen.ni@xxxxxxxxxxxx/
> v7: https://lore.kernel.org/linux-mm/20260515091942.1535677-2-zhen.ni@xxxxxxxxxxxx/
> v6: https://lore.kernel.org/linux-mm/20260511033017.747781-2-zhen.ni@xxxxxxxxxxxx/
> v5: https://lore.kernel.org/linux-mm/20260507064643.179187-2-zhen.ni@xxxxxxxxxxxx/
> v4: https://lore.kernel.org/linux-mm/20260430163247.13628-2-zhen.ni@xxxxxxxxxxxx/
> v3: https://lore.kernel.org/linux-mm/20260428071112.1420380-2-zhen.ni@xxxxxxxxxxxx/
>     https://lore.kernel.org/linux-mm/20260428071112.1420380-3-zhen.ni@xxxxxxxxxxxx/
> v2: https://lore.kernel.org/linux-mm/20260419155540.376847-2-zhen.ni@xxxxxxxxxxxx/
>     https://lore.kernel.org/linux-mm/20260419155540.376847-3-zhen.ni@xxxxxxxxxxxx/
> v1: https://lore.kernel.org/linux-mm/20260417154638.22370-2-zhen.ni@xxxxxxxxxxxx/
>     https://lore.kernel.org/linux-mm/20260417154638.22370-3-zhen.ni@xxxxxxxxxxxx/
> ---
>  mm/page_owner.c | 129 +++++++++++++++++++++++++++++++++++++++++++++---
>  1 file changed, 123 insertions(+), 6 deletions(-)
>

<snip>

> +static ssize_t page_owner_write(struct file *file,
> +				 const char __user *buf,
> +				 size_t count, loff_t *ppos)
> +{
> +	char *kbuf;
> +	char *orig;
> +	char *token;
> +	int ret;
> +	size_t max_input_len;

This can be const size_t max_input_len = 32 with the comment above it.

> +	struct page_owner_filter_state *state = file->private_data;
> +	enum page_owner_print_mode new_print_mode;
> +	unsigned long flags;
> +
> +	/*
> +	 * Maximum input length for filter commands:
> +	 * 32: print_mode command max length is 17 ("mode=stack_handle").
> +	 */
> +	max_input_len = 32;
> +

Otherwise, LGTM.

Acked-by: Zi Yan <ziy@xxxxxxxxxx>

-- 
Best Regards,
Yan, Zi