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Message-ID: <b3e03ae3-36fb-455d-9f62-7e915e7bcd46@linux.dev> Date: Thu, 18 Sep 2025 17:00:58 +0800 From: Ye Liu <ye.liu@...ux.dev> To: Michal Hocko <mhocko@...e.com>, David Hildenbrand <david@...hat.com> Cc: David Hildenbrand <david@...hat.com>, 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 16:49, 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@...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. > > 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
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