On Mon, Sep 16, 2013 at 11:59:20AM +0100, Matt Fleming wrote:
> On Fri, 13 Sep, at 02:38:12PM, jerry.hoemann@xxxxxx wrote:
> > Matt,
> >
> > We have hit an issue on our new platform in development related to the
> > call of efi_reserve_boot_services() from setup_arch().
> >
> > The reservation can interfere with allocation of the crash kernel.
>
> Jerry, thanks for bringing this up.
>
> > In pre 3.9(?) kernels, the crash kernel is required to be allocated from
> > physically contiguous memory below 896 MB.
> >
> > Our new platforms are large in both the amount of memory and the amount
> > of IO. This requires large crash kernels for kdump to work. This is even
> > after the work done for makedumpfile v 1.5 to allow it to work with a
> > smaller foot print.
> >
> >
> > One of the problems is that drivers will allocate memory as boot code and/or
> > data in the region < 896 that effectively fragments this memory.
> > With the reservation, we can't reuse the memory when needed for the
> > crash kernels. If we remove the reservation and allow the kernel
> > to reuse the memory, we the reservation of the crash kernel succeeds.
> >
> > This is definitely a problem for distros that are pre 3.9. Probably less
> > so for top of tree, but i haven't been focused there.
> >
> > So we are definitely interested in finding a mechanism to not
> > do this reservation on platforms that don't have the issues described
> > earlier in this thread.
>
> OK, in an ideal world we'd move the crash kernel reservation after
> efi_free_boot_services(), because at that point the boot regions are
> available again. But it seems that we reserve the boot regions really
> early during startup and release them relatively late. The reason is
> that the Boot Graphics Resource Table (BGRT) data, if present, is
> located in the Boot Services Data regions but we can't extract the
> address of the region from the ACPI tables until we've setup the ACPI
> subsystem, which happens quite late.
>
> I wonder whether performing the reservation of the crash kernel memory
> first, before efi_reserve_boot_services(), would help. That way we'd
> only need to reserve remaining regions in efi_reserve_boot_services().
> This scheme would rely on nothing writing into the crash kernel area
> before we've extracted the BGRT data, however.
>
> --
> Matt Fleming, Intel Open Source Technology Center
Matt,
I conducted the following experiments on a 3.11 kernel:
1) Moved the call of reserve_crashkernel to after efi_free_boot_services.
Booted with crashkernel=512M
a) when memory below 896M was *not* fragmented by BootCode segments
reserve_crashkernel succeeded.
b) when memory below 896M *was* fragmented by BootCode segments
reserve_crashkernel failed.
2) Moved the call to reserve_crashkernel to before call to efi_reserve_boot_services.
Booted with crashkernel=512M
reserve_crashkernel succeeded irrespective of whether the memory below 896M was
fragmented by BootCode segments.
I haven't determined why reserve_crashkernel failed in 1b) above.
I don't see the memory reserved for the crash kernel being accessed
before call to efi_free_boot_services.
CC'ing kexec list for their input as I may have missed something.
Jerry
--
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Jerry Hoemann Software Engineer Hewlett-Packard/MODL
3404 E Harmony Rd. MS 57 phone: (970) 898-1022
Ft. Collins, CO 80528 FAX: (970) 898-XXXX
email: jerry.hoemann@xxxxxx
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