Re: [PATCH 2/2] X86/kdump: fall back to reserve high crashkernel memory

Ingo Molnar
2019-04-21T18:26:15Z

* Dave Young <dyoung@redhat.com> wrote:

> crashkernel=xM tries to reserve crashkernel memory under 4G, which
> is enough for usual cases. But this could fail sometimes, for example
> one tries to reserve a big chunk like 2G, it is possible to fail.
>
> So let the crashkernel=xM just fall back to use high memory in case it
> fails to find a suitable low range. Do not set the ,high as default
> because it allocs extra low memory for DMA buffers and swiotlb, this is
> not always necessary for all machines. Typically like crashkernel=128M
> usually work with low reservation under 4G, so still keep <4G as default.
>
> Signed-off-by: Dave Young <dyoung@redhat.com>
> ---
> Documentation/admin-guide/kernel-parameters.txt | 7 +++++--
> arch/x86/kernel/setup.c | 22 ++++++++++++++--------
> 2 files changed, 19 insertions(+), 10 deletions(-)
>
> --- linux-x86.orig/arch/x86/kernel/setup.c
> +++ linux-x86/arch/x86/kernel/setup.c
> @@ -541,21 +541,27 @@ static void __init reserve_crashkernel(v
> }
>
> /* 0 means: find the address automatically */
> - if (crash_base <= 0) {
> + if (!crash_base) {
> /*
> * Set CRASH_ADDR_LOW_MAX upper bound for crash memory,
> - * as old kexec-tools loads bzImage below that, unless
> - * "crashkernel=size[KMG],high" is specified.
> + * as crashkernel=x,high allocs memory over 4G, also allocs

s/allocs
/allocates

> + * 256M extra low memory for DMA buffers and swiotlb.
> + * but the extra memory is not required for all machines.
> + * So prefer low memory first, and fallback to high memory

s/fallback
/fall back

> + * unless "crashkernel=size[KMG],high" is specified.
> */
> - crash_base = memblock_find_in_range(CRASH_ALIGN,
> - high ? CRASH_ADDR_HIGH_MAX
> - : CRASH_ADDR_LOW_MAX,
> - crash_size, CRASH_ALIGN);
> + if (!high)
> + crash_base = memblock_find_in_range(CRASH_ALIGN,
> + CRASH_ADDR_LOW_MAX,
> + crash_size, CRASH_ALIGN);
> + if (!crash_base)
> + crash_base = memblock_find_in_range(CRASH_ALIGN,
> + CRASH_ADDR_HIGH_MAX,
> + crash_size, CRASH_ALIGN);
> if (!crash_base) {
> pr_info("crashkernel reservation failed - No suitable area found.\n");
> return;
> }
> -
> } else {
> unsigned long long start;
>
> --- linux-x86.orig/Documentation/admin-guide/kernel-parameters.txt
> +++ linux-x86/Documentation/admin-guide/kernel-parameters.txt
> @@ -704,8 +704,11 @@
> upon panic. This parameter reserves the physical
> memory region [offset, offset + size] for that kernel
> image. If '@offset' is omitted, then a suitable offset
> - is selected automatically. Check
> - Documentation/kdump/kdump.txt for further details.
> + is selected automatically.
> + [KNL, x86_64] select a region under 4G first, and
> + fallback to reserve region above 4G in case without

s/fallback
/fall back

> + '@offset'.
> + See Documentation/kdump/kdump.txt for further details.
>
> crashkernel=range1:size1[,range2:size2,...][@offset]
> [KNL] Same as above, but depends on the memory

With the nits fixed:

Reviewed-by: Ingo Molnar <mingo@kernel.org>

Thanks,

Ingo