linux-kernel - Re: [RFC][PATCH v2 22/29] mm/numa: Register information into Kmemdump

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Message-ID: <f43a61b4-d302-4009-96ff-88eea6651e16@linaro.org>
Date: Mon, 4 Aug 2025 15:29:18 +0300
From: Eugen Hristev <eugen.hristev@...aro.org>
To: David Hildenbrand <david@...hat.com>, Michal Hocko <mhocko@...e.com>
Cc: linux-kernel@...r.kernel.org, linux-arm-msm@...r.kernel.org,
 linux-arch@...r.kernel.org, linux-mm@...ck.org, tglx@...utronix.de,
 andersson@...nel.org, pmladek@...e.com,
 linux-arm-kernel@...ts.infradead.org, linux-hardening@...r.kernel.org,
 corbet@....net, mojha@....qualcomm.com, rostedt@...dmis.org,
 jonechou@...gle.com, tudor.ambarus@...aro.org
Subject: Re: [RFC][PATCH v2 22/29] mm/numa: Register information into Kmemdump



On 8/4/25 15:18, David Hildenbrand wrote:
> On 04.08.25 13:06, Eugen Hristev wrote:
>>
>>
>> On 8/4/25 13:54, Michal Hocko wrote:
>>> On Wed 30-07-25 16:04:28, David Hildenbrand wrote:
>>>> On 30.07.25 15:57, Eugen Hristev wrote:
>>> [...]
>>>>> Yes, registering after is also an option. Initially this is how I
>>>>> designed the kmemdump API, I also had in mind to add a flag, but, after
>>>>> discussing with Thomas Gleixner, he came up with the macro wrapper idea
>>>>> here:
>>>>> https://lore.kernel.org/lkml/87ikkzpcup.ffs@tglx/
>>>>> Do you think we can continue that discussion , or maybe start it here ?
>>>>
>>>> Yeah, I don't like that, but I can see how we ended up here.
>>>>
>>>> I also don't quite like the idea that we must encode here what to include in
>>>> a dump and what not ...
>>>>
>>>> For the vmcore we construct it at runtime in crash_save_vmcoreinfo_init(),
>>>> where we e.g., have
>>>>
>>>> VMCOREINFO_STRUCT_SIZE(pglist_data);
>>>>
>>>> Could we similar have some place where we construct what to dump similarly,
>>>> just not using the current values, but the memory ranges?
>>>
>>> All those symbols are part of kallsyms, right? Can we just use kallsyms
>>> infrastructure and a list of symbols to get what we need from there?
>>>
>>> In other words the list of symbols to be completely external to the code
>>> that is defining them?
>>
>> Some static symbols are indeed part of kallsyms. But some symbols are
>> not exported, for example patch 20/29, where printk related symbols are
>> not to be exported. Another example is with static variables, like in
>> patch 17/29 , not exported as symbols, but required for the dump.
>> Dynamic memory regions are not have to also be considered, have a look
>> for example at patch 23/29 , where dynamically allocated memory needs to
>> be registered.
>>
>> Do you think that I should move all kallsyms related symbols annotation
>> into a separate place and keep it for the static/dynamic regions in place ?
> 
> If you want to use a symbol from kmemdump, then make that symbol 
> available to kmemdump.

That's what I am doing, registering symbols with kmemdump.
Maybe I do not understand what you mean, do you have any suggestion for
the static variables case (symbols not exported) ?

> 
> IOW, if we were to rip out kmemdump tomorrow, we wouldn't have to touch 
> any non-kmemdump-specific files.
>