* Dave Young <dyo...@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 <dyo...@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 <mi...@kernel.org> Thanks, Ingo