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

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Message-ID: <23e7ec80-622e-4d33-a766-312c1213e56b@redhat.com>
Date: Mon, 4 Aug 2025 14:18:16 +0200
From: David Hildenbrand <david@...hat.com>
To: Eugen Hristev <eugen.hristev@...aro.org>, 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 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.

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

-- 
Cheers,

David / dhildenb