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

[Dave Young <dyoung@redhat.com>]

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