Re: [PATCH v3 2/4] mm/page_owner: add print_mode filter

zhen.ni
2026-04-29T08:24:50Z

在 2026/4/29 08:57, SeongJae Park 写道:
> On Tue, 28 Apr 2026 15:11:10 +0800 Zhen Ni <zhen.ni@easystack.cn> 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 /
>
> Looks nice to me. I have just trivial cosmetic comments below.
>
>>
>> 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.
>
> I understand the mode was introduced for the stack handle mode, but it exists
> for both full stack and stack handle mode? The wording makes me assume the
> mode is only enabled vs disabled (boolean). It is true that there are only two
> modes, but I feel like this commit message might better written.
>

The commit message could be clearer.

>>
>> Link: https://lore.kernel.org/linux-mm/20260417154638.22370-3-zhen.ni@easystack.cn/
>
> Seems this is a link to v1 of this patch. I think adding the context or moving
> this to the changelog [1] with the brief context explanation would be nice.
>
Good suggestion.

>> 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'
>>
>> Changes in v3:
>> - No code changes
>> ---
>> 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 */
>
> I think this comment should be useful if it was compact_mode. But because now
> it is called print_mode and values have good names that self explaining what
> the mode is, I'm not sure if this comment is really needed.
>

I'll remove the redundant comment

>> + 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);
>> + }
>
> Braces are not needed [2] here?
>
I'll remove the unnecessary braces

Thanks for the detailed review
>> 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
>
> [1] https://docs.kernel.org/process/submitting-patches.html#commentary
> [2] https://docs.kernel.org/process/coding-style.html#placing-braces-and-spaces
>
>
> Thanks,
> SJ
>
>
Best regards,
Zhen Ni