Ok, bisection ended up with:
commit 722bc6b16771ed80871e1fd81c86d3627dda2ac8
Author: WANG Cong <xiyou.wangc...@gmail.com>
Date: Mon Mar 5 15:05:13 2012 -0800
x86/mm: Fix the size calculation of mapping tables
For machines that enable PSE, the first 2/4M memory region still uses
4K pages, so needs more PTEs in this case, but
find_early_table_space() doesn't count this.
And I was able to make the kdump kernel run by reverting back the size
calculations to what they were before. Actually, I am quite confident
that this change is wrong for the 64bit case. The calling function has
some comments about the first 2/4M regions but that is all encapsulated
into #ifdef CONFIG_X86_32.
With some debug output I get this on 64bit (without reverting 77e00000 would be
added to extra space!):
[ 0.000000] init_memory_mapping: [mem 0x00000000-0x77e87fff]
[ 0.000000] [mem 0x00000000-0x77dfffff] page 2M
[ 0.000000] [mem 0x77e00000-0x77e87fff] page 4k
[ 0.000000] mr->end(77e00000)-mr->start(0)=77e00000
[ 0.000000] extra is 88000
[ 0.000000] kernel direct mapping tables up to 0x77e87fff @ [mem
0x1fffc000-0x1fffffff]
So I think there is a substantial amount of space wasted and in the
kdump case this again brings us into trouble of fitting the
initrd+unpacked+kernel. Theoretically the 32bit case should be ok, but I
must admit I never tested that on bare metal. yet.
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Quantal : kexec kernel not triggered when kernel panics
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