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

[Zi Yan]

On 27 Apr 2026, at 23:36, zhen.ni wrote:

> 在 2026/4/27 23:43, Zi Yan 写道:
>> 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
>>
>>
>
> Thanks for the suggestion!
>
> I considered using "full_stack" and "stack_handle" strings, but
> I think the numeric values (0/1) are more concise and easier to type
> for users.

I disagree. It is hard for user to know what the current print mode
is and what available modes are. 0 or 1 is usually for boolean input.

Something like:
[full_stack] stack_handle
full_stack [stack_handle]

is much easier for user to read and use.

>
> The v3 documentation will clarify the meaning:
> - 0 (default): Print full stack traces
> - 1: Print only stack handles
>
> Do you think this is sufficient, or would you still prefer using
> string values instead?
>
>
>> Best Regards,
>> Yan, Zi
>>
>>
> Best regards,
> Zhen


Best Regards,
Yan, Zi