Re: [PATCH] x86, kdump: Set crashkernel_low automatically

From: Vivek Goyal
Date: Mon Mar 18 2013 - 10:46:16 EST

On Mon, Mar 11, 2013 at 12:44:15PM -0700, Yinghai Lu wrote:
> On Mon, Mar 11, 2013 at 12:39 PM, Yinghai Lu <yinghai@xxxxxxxxxx> wrote:
> > On Mon, Mar 11, 2013 at 12:38 PM, Vivek Goyal <vgoyal@xxxxxxxxxx> wrote:
> >>> No need to use crashkernel_high, we can just cashkernel=X@Y instead.
> >>
> >> crashkernel=X@Y is little different. It assumes user knows the memory
> >> map and location "Y" is fixed. There might not be any memory at "Y".
> >
> > then use crashkernel=4G?
> I re attached -v2 and -v3.
> I'm ok that any one is applied or two get applied all together.
> only affect 64bit
> -v2: try under under 896M, then 4G, then MAXMEM
> -v3: auto set crashkernel_low with swiotlb size.

So, what's the resolution on this issue. Is the verdict that we always
reserve high. Update your kexec-tools to cope with that. For swiotlb
issue, modify kexec-tools to copy low memory in backup region and give
low memory to second kernel for software iotlb?

I am assuming that updating tools will not help with loading and using
of 32bit bzImage. So user needs to use crashkernel=X@Y syntax to cope
with that? (Given the fact that copying code around after crash carries
the greater risk of ongoing DMA on destination location).

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