Re: [PATCH] mm/vmstat: add header line to /proc/buddyinfo output

[Ye Liu <ye.liu@linux.dev>]

在 2025/9/18 16:49, Michal Hocko 写道:
> On Thu 18-09-25 16:31:22, Ye Liu wrote:
>>
>>
>> 在 2025/9/18 16:16, David Hildenbrand 写道:
>>> On 18.09.25 10:11, Ye Liu wrote:
>>>>
>>>>
>>>> 在 2025/9/18 15:29, Michal Hocko 写道:
>>>>> On Thu 18-09-25 15:17:40, Ye Liu wrote:
>>>>>> From: Ye Liu <liuye@kylinos.cn>
>>>>>>
>>>>>> Add a header line to /proc/buddyinfo that shows the order numbers
>>>>>> for better readability and clarity.
>>>>>>
>>>>>> Before:
>>>>>> Node 0, zone      DMA      0      0      0      0      0      0      0 ...
>>>>>> Node 0, zone    DMA32      5      8      6      6      7      5      8 ...
>>>>>> Node 0, zone   Normal   1113    351    138     65     38     31     25 ...
>>>>>>
>>>>>> After:
>>>>>> Free pages per order       0      1      2      3      4      5      6 ...
>>>>>> Node 0, zone      DMA      0      0      0      0      0      0      0 ...
>>>>>> Node 0, zone    DMA32      5      8      6      6      7      5      8 ...
>>>>>> Node 0, zone   Normal   1113    351    138     65     38     31     25 ...
>>>>>
>>>>> Why is this needed? And have you considered tha this might break
>>>>> existing parsers of the file?
>>>>>
>>>>
>>>> Thanks for the review.
>>>>
>>>> The reason for this change is simply to make /proc/buddyinfo self-describing.
>>>> Right now you have to know which column is which order; with a header it’s
>>>> obvious. This is similar to what /proc/pagetypeinfo already does, e.g.:
>>>>
>>>>    Page block order: 9
>>>>    Pages per block: 512
>>>>
>>>>    Free pages count per migrate type at order   0 1 2 3 ...
>>>>    Node 0, zone DMA, type Unmovable             0 0 0 ...
>>>>
>>>> Regarding existing parsers: the patch does not change any of the existing
>>>> “Node … zone …” lines, it only adds a single header line before them. Most
>>>> parsers match “Node” lines and ignore everything else, so the risk should be
>>>> low. If you know of any existing parser that this would break, please let
>>>> me know so I can address it.
>>>
>>> What if there is a single one out there that has hardcoded to skip the first line only?
>>
>> I understand there may be no way to be fully compatible with all existing
>> parsers. However, /proc/buddyinfo is essentially raw data intended for
>> human and tool consumption, and parsers are expected to be robust against
>> format changes.
> 
> I am pretty sure you can create a trivial wrapper to print that header,
> right?
> 
>> Adding a '#' prefix to the header would allow most parsers to skip it,
>> but it still changes the file output and cannot fully guarantee that no
>> external tool will be affected.                                          
> 
> That still assumes that they expect something like that.
> We are trying really hard to not break existing userspace even if it is
> not written in a robust way. That is simply how Linux kernel handles all
> the existing interfaces. There must be a very serious reason to add a
> change that might _theoretically_ breaker existing userspace. What you
> are proposing here is not such a reason as it is trivial to achieve what
> you want from the userspace.
> 
> NAK to the change.

I’ll drop this change.

-- 
Thanks,
Ye Liu