On Thu, Jun 26, 2008 at 09:54:08PM +0200, Bernhard Walle wrote:
> This patch removes the need of the crashkernel=... at offset parameter to define
> a fixed offset for crashkernel reservation. That feature can be used together
> with a relocatable kernel where the kexec-tools relocate the kernel and
> get the actual offset from /proc/iomem.
>
> The use case is a kernel where the .text+.data+.bss is after 16M physical
> memory (debug kernel with lockdep on x86_64 can cause that) which caused a
> major pain in autoconfiguration in our distribution.
>
> Also, that patch unifies crashdump architectures a bit since IA64 has
> that semantics from the very beginning of the kdump port.
>
> Please provide feedback!
>
Hi Bernhard,
This looks like a good idea. That means distributions don't have to
hardcode the crashbase at 16MB and the decision to find a free memory
can be left on kernel. Users will also find it easy that way.
>
> Signed-off-by: Bernhard Walle <bwalle at suse.de>
> ---
> arch/x86/kernel/setup.c | 70 +++++++++++++++++++++++++++++++++++------------
> 1 files changed, 52 insertions(+), 18 deletions(-)
>
> diff --git a/arch/x86/kernel/setup.c b/arch/x86/kernel/setup.c
> index a81d82c..c30bb7b 100644
> --- a/arch/x86/kernel/setup.c
> +++ b/arch/x86/kernel/setup.c
> @@ -435,6 +435,34 @@ static inline unsigned long long get_total_mem(void)
> }
>
> #ifdef CONFIG_KEXEC
> +
> +/**
> + * Reserve @size bytes of crashkernel memory at any suitable offset.
> + *
> + * @size: Size of the crashkernel memory to reserve.
> + * Returns the base address on success, and -1ULL on failure.
> + */
> +unsigned long long find_and_reserve_crashkernel(unsigned long long size)
> +{
> + const unsigned long long alignment = 16<<20; /* 16M */
> + unsigned long long start = 0LL;
> +
> + while (1) {
> + int ret;
> +
> + start = find_e820_area(start, ULONG_MAX, size, alignment);
> + if (start == -1ULL)
> + return start;
> +
> + /* try to reserve it */
> + ret = reserve_bootmem_generic(start, size, BOOTMEM_EXCLUSIVE);
> + if (ret >= 0)
> + return start;
> +
> + start += alignment;
> + }
I think both i386 and x86_64 relocatable kernels had some upper limits
where these could be loaded (Eric had mentioned those in the patch. I
don't remember these). It might be a good idea to capture it here
making sure "start" does not cross those limits otherwise don't reserve
the memory.
Thanks
Vivek
