On Thu, Dec 16, 2021 at 10:46:12AM +0800, Leizhen (ThunderTown) wrote:
> The original value (1ULL << 32) is inaccurate
I keep asking *why*?
> and it enlarged the CRASH_ADDR_LOW upper limit.
$ git grep -E "CRASH_ADDR_LOW\W"
$
I have no clue what you mean here.
> This is because when the memory is allocated from the low end, the
> address cannot exceed CRASH_ADDR_LOW_MAX, see "if (!high)" branch.
> If
> the memory is allocated from the high end, 'crash_base' is greater than or
> equal to (1ULL << 32), and naturally, it is greater than CRASH_ADDR_LOW_MAX.
>
> I think I should update the description, thanks.
I think you should explain why is (1ULL << 32) wrong.
It came from:
eb6db83d1059 ("x86/setup: Do not reserve crashkernel high memory if low reservation failed")
which simply frees the high memory portion when the low reservation
fails. And the test for that is, is crash base > 4G. So that makes
perfect sense to me.
So your change is a NOP on 64-bit and it is a NOP on 32-bit by virtue of
the _low() variant always returning 0 on 32-bit.
--
Regards/Gruss,
Boris.
https://people.kernel.org/tglx/notes-about-netiquette
