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

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Message-ID: <780aa9d6-a85c-4050-820e-c0ca9f5bb658@redhat.com>
Date: Thu, 18 Sep 2025 10:16:16 +0200
From: David Hildenbrand <david@...hat.com>
To: Ye Liu <ye.liu@...ux.dev>, 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

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?

-- 
Cheers

David / dhildenb