Re: [PATCH v2 2/3] mm/page_owner: add print_mode filter

[Zi Yan]

On 19 Apr 2026, at 11:55, Zhen Ni wrote:

> Add print_mode functionality to reduce page_owner output size by
> printing only the stack handle instead of the full stack trace.
>
> Example output with print_mode enabled:
>   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(referenced|lru|active|private|node=3|zone=0|
> lastcpupid=0x1ffff)
>   handle: 17432583
>   Charged to memcg /
>
> Print mode significantly reduces output size while preserving all
> other page allocation information. The correspondence between handles
> and stack traces can be obtained through the show_stacks_handles interface.
>
> Link: https://lore.kernel.org/linux-mm/20260417154638.22370-3-zhen.ni@xxxxxxxxxxxx/
> Suggested-by: Zi Yan <ziy@xxxxxxxxxx>
> Signed-off-by: Zhen Ni <zhen.ni@xxxxxxxxxxxx>
> ---
>
> 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'
> ---
>  mm/page_owner.c | 28 +++++++++++++++++++++++++++-
>  1 file changed, 27 insertions(+), 1 deletion(-)
>
> diff --git a/mm/page_owner.c b/mm/page_owner.c
> index 5884d883837e..6d87b6948cfa 100644
> --- a/mm/page_owner.c
> +++ b/mm/page_owner.c
> @@ -590,7 +590,13 @@ print_page_owner(char __user *buf, size_t count, unsigned long pfn,
>  			migratetype_names[pageblock_mt],
>  			&page->flags);
>
> -	ret += stack_depot_snprint(handle, kbuf + ret, count - ret, 0);
> +	/* Print mode: full stack or stack handle */
> +	if (READ_ONCE(owner_filter.print_mode) == PAGE_OWNER_PRINT_STACK_HANDLE) {
> +		ret += scnprintf(kbuf + ret, count - ret,
> +				"handle: %d\n", handle);
> +	} else {
> +		ret += stack_depot_snprint(handle, kbuf + ret, count - ret, 0);
> +	}
>  	if (ret >= count)
>  		goto err;
>
> @@ -985,6 +991,24 @@ static int page_owner_threshold_set(void *data, u64 val)
>  DEFINE_SIMPLE_ATTRIBUTE(page_owner_threshold_fops, &page_owner_threshold_get,
>  			&page_owner_threshold_set, "%llu");
>
> +static int page_owner_print_mode_get(void *data, u64 *val)
> +{
> +	*val = READ_ONCE(owner_filter.print_mode);
> +	return 0;
> +}
> +
> +static int page_owner_print_mode_set(void *data, u64 val)
> +{
> +	if (val > PAGE_OWNER_PRINT_STACK_HANDLE)
> +		return -EINVAL;
> +	WRITE_ONCE(owner_filter.print_mode, val);
> +	return 0;
> +}
> +
> +DEFINE_SIMPLE_ATTRIBUTE(page_owner_print_mode_fops,
> +			&page_owner_print_mode_get,
> +			&page_owner_print_mode_set, "%lld");
> +
>
>  static int __init pageowner_init(void)
>  {
> @@ -998,6 +1022,8 @@ static int __init pageowner_init(void)
>  	debugfs_create_file("page_owner", 0400, NULL, NULL, &page_owner_fops);
>
>  	filter_dir = debugfs_create_dir("page_owner_filter", NULL);
> +	debugfs_create_file("print_mode", 0600, filter_dir, NULL,
> +			    &page_owner_print_mode_fops);
>
>  	dir = debugfs_create_dir("page_owner_stacks", NULL);
>  	debugfs_create_file("show_stacks", 0400, dir,
> -- 
> 2.20.1

I think it is more user-friendly to use “full_stack” and “stack_handle”
instead of 0 and 1. You can refer to [1] to sysfs_match_string() to
do that. I was testing the interface, but needed to look at your code
to know which print_mode I am using. ;)


[1] https://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm.git/tree/mm/huge_memory.c?h=mm-everything#n380


Best Regards,
Yan, Zi