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

From: H. Peter Anvin
Date: Mon Mar 11 2013 - 15:07:23 EST

On 03/11/2013 12:02 PM, Vivek Goyal wrote:
>> What is the purpose of reserving that kind of memory below 896 MB? If
>> you have a 32-bit system, it will likely be useless since you are
>> robbing the primary of most of lowmem, on a 64-bit system 896 MB is not
>> a magic value in any way...?
> Actually I am not sure where did 896MB magic value had come from for
> x86_64 so far. I assumed that it was some kexec-tools limitation so
> first trying 896MB will preserve working with old kexec-tools. If it
> was some kernel limitation, then I agree it should not be required anymore.
> I do remember that old pugatory had 2G limit. So may be we can first
> try reserve with-in first 2G, then with-in first 4G and then above
> 4G. (Assuming 896M was not kexec-tools limitation and had something
> to do with kernel/initramfs).

It is obvious where it *originated* from... it is the *default* (but not
necessarily the actual!) HIGHMEM crossover point on x86-32.

Whether this limitation has crept into somewhere else is a good question.


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