crashkernel=512M is no longer working on this aarch64 server

From: Qian Cai
Date: Sat Nov 10 2018 - 23:41:59 EST

It was broken somewhere between b00d209241ff and 3541833fd1f2.

[ 0.000000] cannot allocate crashkernel (size:0x20000000)

Where a good one looks like this,

[ 0.000000] crashkernel reserved: 0x0000000008600000 - 0x0000000028600000 (512 MB)

Some commits look more suspicious than others.

mm: add mm_pxd_folded checks to pgtable_bytes accounting functions
mm: introduce mm_[p4d|pud|pmd]_folded
mm: make the __PAGETABLE_PxD_FOLDED defines non-empty

# diff -u ../iomem.good.txt ../iomem.bad.txt
--- ../iomem.good.txt 2018-11-10 22:28:20.092614398 -0500
+++ ../iomem.bad.txt 2018-11-10 20:39:54.930294479 -0500
@@ -1,9 +1,8 @@
00000000-3965ffff : System RAM
00080000-018cffff : Kernel code
- 018d0000-020affff : reserved
- 020b0000-045affff : Kernel data
- 08600000-285fffff : Crash kernel
- 28730000-2d5affff : reserved
+ 018d0000-0762ffff : reserved
+ 07630000-09b2ffff : Kernel data
+ 231b0000-2802ffff : reserved
30ec0000-30ecffff : reserved
35660000-3965ffff : reserved
39660000-396fffff : reserved
@@ -127,7 +126,7 @@
7c5200000-7c520ffff : 0004:48:00.0
1040000000-17fbffffff : System RAM
13fbfd0000-13fdfdffff : reserved
- 16fba80000-17fbfdffff : reserved
+ 16fafd0000-17fbfdffff : reserved
17fbfe0000-17fbffffff : reserved
1800000000-1ffbffffff : System RAM
1bfbff0000-1bfdfeffff : reserved

The memory map looks like this,

[ 0.000000] ACPI: Early table checksum verification disabled
[ 0.000000] ACPI: RSDP 0x00000000398D0014 000024 (v02 HISI )
[ 0.000000] ACPI: XSDT 0x00000000398C00E8 000064 (v01 HISI HIP07 00000000 01000013)
[ 0.000000] ACPI: FACP 0x0000000039770000 000114 (v06 HISI HIP07 00000000 INTL 20151124)
[ 0.000000] ACPI: DSDT 0x0000000039730000 00691A (v02 HISI HIP07 00000000 INTL 20170728)
[ 0.000000] ACPI: MCFG 0x00000000397C0000 0000AC (v01 HISI HIP07 00000000 INTL 20151124)
[ 0.000000] ACPI: SLIT 0x00000000397B0000 00003C (v01 HISI HIP07 00000000 INTL 20151124)
[ 0.000000] ACPI: SRAT 0x00000000397A0000 000578 (v03 HISI HIP07 00000000 INTL 20151124)
[ 0.000000] ACPI: DBG2 0x0000000039790000 00005A (v00 HISI HIP07 00000000 INTL 20151124)
[ 0.000000] ACPI: GTDT 0x0000000039760000 00007C (v02 HISI HIP07 00000000 INTL 20151124)
[ 0.000000] ACPI: APIC 0x0000000039750000 0014E4 (v04 HISI HIP07 00000000 INTL 20151124)
[ 0.000000] ACPI: IORT 0x0000000039740000 000554 (v00 HISI HIP07 00000000 INTL 20170728)
[ 0.000000] ACPI: SRAT: Node 0 PXM 0 [mem 0x00000000-0x3fffffff]
[ 0.000000] ACPI: SRAT: Node 1 PXM 1 [mem 0x1800000000-0x1fffffffff]
[ 0.000000] ACPI: SRAT: Node 0 PXM 0 [mem 0x1000000000-0x17ffffffff]
[ 0.000000] ACPI: SRAT: Node 3 PXM 3 [mem 0x9000000000-0x97ffffffff]
[ 0.000000] ACPI: SRAT: Node 2 PXM 2 [mem 0x8800000000-0x8fffffffff]
[ 0.000000] NUMA: NODE_DATA [mem 0x17fbffe5c0-0x17fbffffff]
[ 0.000000] NUMA: NODE_DATA [mem 0x1ffbffe5c0-0x1ffbffffff]
[ 0.000000] NUMA: NODE_DATA [mem 0x8ffbffe5c0-0x8ffbffffff]
[ 0.000000] NUMA: NODE_DATA [mem 0x97fadce5c0-0x97fadcffff]
[ 0.000000] Zone ranges:
[ 0.000000] DMA32 [mem 0x0000000000000000-0x00000000ffffffff]
[ 0.000000] Normal [mem 0x0000000100000000-0x00000097fbffffff]
[ 0.000000] Movable zone start for each node
[ 0.000000] Early memory node ranges
[ 0.000000] node 0: [mem 0x0000000000000000-0x000000003965ffff]
[ 0.000000] node 0: [mem 0x0000000039660000-0x00000000396fffff]
[ 0.000000] node 0: [mem 0x0000000039700000-0x000000003977ffff]
[ 0.000000] node 0: [mem 0x0000000039780000-0x000000003978ffff]
[ 0.000000] node 0: [mem 0x0000000039790000-0x00000000397cffff]
[ 0.000000] node 0: [mem 0x00000000397d0000-0x00000000398bffff]
[ 0.000000] node 0: [mem 0x00000000398c0000-0x00000000398dffff]
[ 0.000000] node 0: [mem 0x00000000398e0000-0x0000000039d5ffff]
[ 0.000000] node 0: [mem 0x0000000039d60000-0x000000003ed4ffff]
[ 0.000000] node 0: [mem 0x000000003ed50000-0x000000003ed7ffff]
[ 0.000000] node 0: [mem 0x000000003ed80000-0x000000003fbfffff]
[ 0.000000] node 0: [mem 0x0000001040000000-0x00000017fbffffff]
[ 0.000000] node 1: [mem 0x0000001800000000-0x0000001ffbffffff]
[ 0.000000] node 2: [mem 0x0000008800000000-0x0000008ffbffffff]
[ 0.000000] node 3: [mem 0x0000009000000000-0x00000097fbffffff]