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

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Message-ID: <6d6e2e33-c221-4ab8-a29b-3d14fb1a592c@linux.dev>
Date: Thu, 18 Sep 2025 16:31:22 +0800
From: Ye Liu <ye.liu@...ux.dev>
To: David Hildenbrand <david@...hat.com>, Michal Hocko <mhocko@...e.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>, Ye Liu <liuye@...inos.cn>,
 Lorenzo Stoakes <lorenzo.stoakes@...cle.com>,
 "Liam R. Howlett" <Liam.Howlett@...cle.com>, Vlastimil Babka
 <vbabka@...e.cz>, Mike Rapoport <rppt@...nel.org>,
 Suren Baghdasaryan <surenb@...gle.com>, linux-mm@...ck.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm/vmstat: add header line to /proc/buddyinfo output

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@...inos.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.

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.                                          

> 

-- 
Thanks,
Ye Liu