On 01/13/2014 03:31 PM, KOSAKI Motohiro wrote: > On Sun, Jan 12, 2014 at 6:46 PM, Prarit Bhargava <prarit@xxxxxxxxxx> wrote: >> >> >> On 01/11/2014 11:35 AM, 7eggert@xxxxxx wrote: >>> >>> >>> On Fri, 10 Jan 2014, Prarit Bhargava wrote: >>> >>>> kdump uses memmap=exactmap and mem=X values to configure the memory >>>> mapping for the kdump kernel. If memory is hotadded during the boot of >>>> the kdump kernel it is possible that the page tables for the new memory >>>> cause the kdump kernel to run out of memory. >>>> >>>> Since the user has specified a specific mapping ACPI Memory Hotplug should be >>>> disabled in this case. >>> >>> I'll ask just in case: Is it possible to want memory hotplug in spite of >>> using memmap=exactmap or mem=X? >> >> Good question -- I can't think of a case. When a user specifies "memmap" or >> "mem" IMO they are asking for a very specific memory configuration. Having >> extra memory added above what the user has specified seems to defeat the purpose >> of "memmap" and "mem". > > May be yes, may be no. > > They are often used for a wrokaround to avoid broken firmware issue. > If we have no way > to explicitly enable hotplug. We will lose a workaround. > > Perhaps, there is no matter. Today, memory hotplug is only used on > high-end machine > and their firmware is carefully developped and don't have a serious > issue almostly. Though. Oof -- sorry Kosaki :( I didn't see this until just now (and your subsequent ACK on the updated patch). I just remembered that we did have a processor vendor's whitebox that would not boot unless we specified a specific memmap and we did specify memmap=exactmap to boot the system correctly and the system had hotplug memory. So it means that I should not key off of "memmap=exactmap". I will self-NAK the updated patch and submit a new one. P. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>