[Bug 785394] Re: Hard-coded crashkernel=... memory reservation in /etc/grub.d/10_linux is insufficient

[Andy Whitcroft]

It seems that the default is to use the current kernel and initrd for
the kexec kernel.  This is going to consume some 36MB of this 64MB
window, another 4.5 for the kernel itself and we down to close to 20MB
of memory left to boot in, which seems to be asking a lot.

It seems we could be a little more targetted in our use of a special
initrd for this purpose.

** Changed in: kexec-tools (Ubuntu)
       Status: New => In Progress

** Changed in: kexec-tools (Ubuntu)
     Assignee: (unassigned) => Andy Whitcroft (apw)

** Changed in: kexec-tools (Ubuntu)
   Importance: Undecided => Medium

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https://bugs.launchpad.net/bugs/785394

Title:
  Hard-coded crashkernel=... memory reservation in /etc/grub.d/10_linux
  is insufficient

Status in “grub2” package in Ubuntu:
  New
Status in “kexec-tools” package in Ubuntu:
  In Progress

Bug description:
  Binary package hint: grub-pc

  This concerns grub-pc 1.99~rc1-13ubuntu3 in Ubuntu Natty.

  The /etc/grub.d/10_linux file contains this snippet:

      # add crashkernel option if we have the required tools
      if [ -x "/usr/bin/makedumpfile" ] && [ -x "/sbin/kexec" ]; then
          GRUB_CMDLINE_EXTRA="$GRUB_CMDLINE_EXTRA crashkernel=384M-2G:64M,2G-:128M"
      fi

  I am on a system with 2GB of RAM (reported as 2038MB), and according
  to the kernel startup messages, 64MB is reserved for the crash kernel.

  Unfortunately, this does not appear to be enough memory for the
  regular Ubuntu kernel to boot. I am attaching a kernel log obtained
  via serial cable; it shows the initial boot, a crash in the kernel's
  video-driver-related code, the subsequent crashkernel boot, and then
  an apparent "out of memory" kernel panic. (A side effect of the
  "double crash" is that the system is left unresponsive, requiring a
  manual reset instead of rebooting itself automatically.)

  If I double the memory numbers in the crashkernel=... argument, so
  that the reservation is 128MB, the system correctly goes on to attempt
  a vmcore dump and reboot.