kdump: No udev events for memory hotplug?

Américo Wang xiyou.wangcong at gmail.com
Thu Oct 27 03:45:44 EDT 2011

On Thu, Oct 27, 2011 at 12:08 AM, Michael Holzheu
<holzheu at linux.vnet.ibm.com> wrote:
> Hello Vivek and Eric,


> I noticed that on my system kernel 3.1 *no* udev events for memory
> hotplug are generated. Same on my RHEL6.1.
> # udevadm monitor
> # echo offline > /sys/devices/system/memory/memory4/state
> -> No event
> But we need the udev events in order to do a kdump reload for setting up
> the ELF loads correctly.
> In my /etc/udev/rules.d/98-kexec.rules there are rules for memory
> hotplug:
> SUBSYSTEM=="memory", ACTION=="add", PROGRAM="/etc/init.d/kdump restart"
> SUBSYSTEM=="memory", ACTION=="remove", PROGRAM="/etc/init.d/kdump
> restart"
> Perhaps/probably I am missing something?

As Heiko pointed out, probably the memory-hotplug subsystem doesn't implement
uevent, this is why you can't get uevent when you hot-remove the memory.

For kdump, the memory is reserved by "crashkernel=", it is determined during
boot (but you can shrink it after boot), so it is not aware of memory hotplug.
IOW, if you hot-remove the memory where the crash kernel stays, the
'kdump restart'
will fail. But yes, restarting kdump can rebuild the memmap and ELF headers.


More information about the kexec mailing list