On Mon, Jan 28, 2019 at 11:18:31AM +0100, Borislav Petkov wrote:
> On Mon, Jan 28, 2019 at 05:58:09PM +0800, Dave Young wrote:
> > Another reason is in case ,high we will need automatically reserve a
> > region in low area for swiotlb. So for example one use
> > crashkernel=256M,high, actual reserved memory is 256M above 4G and
> > another 256M under 4G for swiotlb. Normally it is not necessary for
> > most people. Thus we can not make ,high as default.
>
> And how is the poor user to figure out that we decided for her/him that
> swiotlb reservation is something not necessary for most people and thus
> we fail the crashkernel= reservation?
>
> IOW, that "logic" above doesn't make a whole lot of sense to me from
> user friendliness perspective.
So to show what I mean: I'm trying to reserve a crash kernel region on a
box here. I tried:
crashkernel=64M@16M
as it is stated in Documentation/kdump/kdump.txt.
Box said:
[ 0.000000] crashkernel reservation failed - memory is in use.
Oh great.
Then I tried:
crashkernel=64M@64M
Box said:
[ 0.000000] crashkernel reservation failed - memory is in use.
So I simply did:
crashkernel=64M
and the box said:
[ 0.000000] Reserving 64MB of memory at 3392MB for crashkernel (System RAM: 16271MB)
So I could've gone a long time poking at the memory to find a suitable
address.
So do you see what I mean with making this as user-friendly and as
robust as possible?
In this case I don't care about *where* my crash kernel is - I only want
to have one loaded *somewhere*.
And the same strategy should be applied to other reservation attempts
- we should try hard to reserve and if we cannot reserve, then try an
alternating range.
I even think that
crashkernel=X@Y
should not simply fail if Y is occupied but keep trying and say
[ 0.000000] Reserving 64MB of memory at alternative address 3392MB for crashkernel (System RAM: 16271MB)
and only fail when the user doesn't really want the kernel to try hard
by booting with
crashkernel=X@Y,strict
But that's for another day.
--
Regards/Gruss,
Boris.
Good mailing practices for 400: avoid top-posting and trim the reply.
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