There is already documentation about it. For example, from
https://ubuntu.com/server/docs/kernel-crash-dump

"If the dump does not work due to OOM (Out Of Memory) error, then try
increasing the amount of reserved memory by editing
/etc/default/grub.d/kdump-tools.cfg. For example, to reserve 512
megabytes"

There are multiple reasons why an OOM might happen during kdump, and
there are no plans on detecting them on a case-by-case, so we won't do
it for this specific case of root volume decryption.

If we use a very large default that might work on almost all cases, it
will take much more memory than is necessary for many users. On the
other hand, using a default that won't work for most users is not any
better.

So, noticing that any default will affect all users, including those
that do not enable root volume encryption or do not use argon2i; we have
3 options for the new default:

1) Keep 2G-4G:384M; some users won't be able to collect kdump unless they 
reconfigure the crashkernel option, but most users will, by reserving not more 
than 384M from a 2G VM.
2) Raise it to 2G-4G: 512M, it reserves more memory, and users with 2G to 4G 
VMs using argon2i for root volume encryption might be able to collect kdump for 
the sake of reserving more memory by default for users that don't use root 
volume encryption.
3) Remove the 2G-4G section of crashkernel: users with VMs smaller than 4G 
won't be able to collect kdump unless they configure and test a crashkernel 
configuration by themselves.

I still think the first option is the better one.

Cascardo.

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https://bugs.launchpad.net/bugs/1877533

Title:
  [20.10 FEAT] Increase the crashkernel setting if the root volume is
  luks2-encrypted

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