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

Dave Young
2019-04-22T03:03:17Z

On 04/21/19 at 08:26pm, Ingo Molnar wrote:
>
> * 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 for review, will reply to 2/2 with an update of those spelling
issues.

Dave