lkml.org 
[lkml]   [2014]   [Jan]   [13]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH 2/2] x86, e820 disable ACPI Memory Hotplug if memory mapping is specified by user [v2]


On 01/13/2014 03:31 PM, KOSAKI Motohiro wrote:
> On Sun, Jan 12, 2014 at 6:46 PM, Prarit Bhargava <prarit@redhat.com> wrote:
>>
>>
>> On 01/11/2014 11:35 AM, 7eggert@gmx.de 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.




\
 
 \ /
  Last update: 2014-01-14 01:21    [W:0.088 / U:0.104 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site