On 10/24/17 at 01:31pm, Dave Young wrote: > Now crashkernel=X will fail if there's not enough memory at low region > (below 896M) when trying to reserve large memory size. One can use > crashkernel=xM,high to reserve it at high region (>4G) but it is more > convinient to improve crashkernel=X to: > > - First try to reserve X below 896M (for being compatible with old > kexec-tools). > - If fails, try to reserve X below 4G (swiotlb need to stay below 4G). > - If fails, try to reserve X from MAXMEM top down. > > It's more transparent and user-friendly. > > If crashkernel is large and the reserved is beyond 896M, old kexec-tools > is not compatible with new kernel because old kexec-tools can not load > kernel at high memory region, there was an old discussion below: > https://lkml.org/lkml/2013/10/15/601 > > But actually the behavior is consistent during my test. Suppose > old kernel fail to reserve memory at low areas, kdump does not > work because no meory reserved. With this patch, suppose new kernel > successfully reserved memory at high areas, old kexec-tools still fail > to load kdump kernel (tested 2.0.2), so it is acceptable, no need to > worry about the compatibility. > > Here is the test result (kexec-tools 2.0.2, no high memory load > support): > Crashkernel over 4G: > # cat /proc/iomem|grep Crash > be000000-cdffffff : Crash kernel > 213000000-21effffff : Crash kernel > # ./kexec -p /boot/vmlinuz-`uname -r` > Memory for crashkernel is not reserved > Please reserve memory by passing "crashkernel=X at Y" parameter to the kernel > Then try loading kdump kernel > > crashkernel: 896M-4G: > # cat /proc/iomem|grep Crash > 96000000-cdefffff : Crash kernel > # ./kexec -p /boot/vmlinuz-4.14.0-rc4+ > ELF core (kcore) parse failed > Cannot load /boot/vmlinuz-4.14.0-rc4+ > > Signed-off-by: Dave Young <dyoung at redhat.com> > --- > arch/x86/kernel/setup.c | 16 ++++++++++++++++ > 1 file changed, 16 insertions(+) > > --- linux-x86.orig/arch/x86/kernel/setup.c > +++ linux-x86/arch/x86/kernel/setup.c > @@ -568,6 +568,22 @@ static void __init reserve_crashkernel(v > high ? CRASH_ADDR_HIGH_MAX > : CRASH_ADDR_LOW_MAX, > crash_size, CRASH_ALIGN); > +#ifdef CONFIG_X86_64 > + /* > + * crashkernel=X reserve below 896M fails? Try below 4G > + */ > + if (!high && !crash_base) > + crash_base = memblock_find_in_range(CRASH_ALIGN, > + (1ULL << 32), > + crash_size, CRASH_ALIGN); > + /* > + * crashkernel=X reserve below 4G fails? Try MAXMEM > + */ > + if (!high && !crash_base) > + crash_base = memblock_find_in_range(CRASH_ALIGN, > + CRASH_ADDR_HIGH_MAX, > + crash_size, CRASH_ALIGN); > +#endif > if (!crash_base) { > pr_info("crashkernel reservation failed - No suitable area found.\n"); > return; > > Andrew, this patch is good to have, could you take this in your tree? The other two patches may need more discussion I will drop them for now. Thanks Dave
