Oh!! I'm so sorry Jan Beulich.
It is my first time to use this mailing list.
Please understand my fault, this time only.

Anyway, as you mentioned, I added below line in '/etc/default/grub' file
and reboot:
> GRUB_CMDLINE_XEN="crashkernel=384M-:256M@64M"
Then,
1. I cannot see anything when I type "grep -i crash /proc/iomem"
2. I can see kernel log of Xen hypervisor when I type "sudo xl dmesg | grep
-i crash":
(XEN) Command line: placeholder crashkernel=384M-:256M@64M

I suppose a 'crashkernel' cmdline option of either Xen hypervisor or Dom0
kernel can be enabled.
I know it is quite difficult to advise some problems online but, could you
give me a piece of hint?

Sincerely,

On Mon, Aug 28, 2017 at 6:13 PM, Jan Beulich <JBeulich@suse.com> wrote:

> >>> On 28.08.17 at 11:04, <nickeysgo@gmail.com> wrote:
> > Thank you for your reply.
> > I checked what you mentioned(Xen command line).
> > But I could not find where the Xen command line configuration.
> > As I think, it would be in /etc/default/grub file because Dom0 is used
> for
> > booting like native system.
> > Is it wrong? I didn't get your point?
>
> First of all - please avoid private mails. Keep the list Cc-ed.
>
> And then - I can't tell you how to configure your variant of grub.
> All I can tell you is that the option you're after needs to be
> passed to Xen.
>
> Jan
>
>