On 9/30/22 12:40, Borislav Petkov wrote:
On Fri, Sep 30, 2022 at 12:11:26PM -0500, Eric DeVolder wrote:
There is of course a way to enumerate the memory regions in use on the
machine, that is not what this code needs. In order to compute the maximum
buffer size needed (this buffer size is computed once), the count of the
maximum number of memory regions possible (even if not currently in use) is
what is needed.

Isn't that max number documented somewhere in memory hotplug docs?

Because then you don't need that Kconfig item either. Imagine you're a
distro kernel distributor and you want crash to work on all machines
your kernel works.

So you go and set that number to max. And that would be the 99% of the
kernel configs out there.

Which means, you can just set it to max without a Kconfig item.

Oh, that would be an error of haste on my part. This should be:
   depends on CRASH_DUMP && MEMORY_HOTPLUG

You need a Kconfig item which enables all this gunk as MEMORY_HOTPLUG is
not a omnipresent feature. And that Kconfig item should depend on the
other Kconfig items of the technology you need.

I once had CONFIG_CRASH_HOTPLUG, but you disagreed.

https://lore.kernel.org/lkml/ylgot+ludql+g%2...@zn.tnic/

From there I simply went with

 #if defined(CONFIG_HOTPLUG_CPU) || defined(CONFIG_MEMORY_HOTPLUG)

which route do you prefer?

Thanks!
eric


Baoquan pointed me to:

https://lore.kernel.org/lkml/cover.1656659357.git.naveen.n....@linux.vnet.ibm.com/T/

In that thread says:

"- arch_kexec_apply_relocations_add() is only overridden by x86 and s390.
   Retain the function prototype for those and move the weak
   implementation into the header as a static inline for other
   architectures."

So yes, that's even better.


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