x86/kdump: crashkernel=X try to reserve below 896M first then below 4G and MAXMEM

[Yinghai Lu]

On Thu, Oct 19, 2017 at 10:52 PM, Dave Young <dyoung at redhat.com> wrote:
> Now crashkernel=X will fail if there's not enough memory at low region
> (below 896M) when trying to reserve large memory size.  One can use
> crashkernel=xM,high to reserve it at high region (>4G) but it is more
> convinient to improve crashkernel=X to:
>
>  - First try to reserve X below 896M (for being compatible with old
>    kexec-tools).
>  - If fails, try to reserve X below 4G (swiotlb need to stay below 4G).
>  - If fails, try to reserve X from MAXMEM top down.
>
> It's more transparent and user-friendly.

ok with me.

But looks like last time Vivek did not like this idea.