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

["zhen.ni" <zhen.ni@easystack.cn>]

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@easystack.cn/
>> Suggested-by: Zi Yan <ziy@nvidia.com>
>> Signed-off-by: Zhen Ni <zhen.ni@easystack.cn>
>> ---
>>
>> 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.

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