x86_64: SPARSEMEM_VMEMMAP 2M page size support

x86_64 uses 2M page table entries to map its 1-1 kernel space.  We also
implement the virtual memmap using 2M page table entries.  So there is no
additional runtime overhead over FLATMEM, initialisation is slightly more
complex.  As FLATMEM still references memory to obtain the mem_map pointer and
SPARSEMEM_VMEMMAP uses a compile time constant, SPARSEMEM_VMEMMAP should be
superior.

With this SPARSEMEM becomes the most efficient way of handling virt_to_page,
pfn_to_page and friends for UP, SMP and NUMA on x86_64.

[apw@shadowen.org: code resplit, style fixups]
[apw@shadowen.org: vmemmap x86_64: ensure end of section memmap is initialised]
Signed-off-by: Christoph Lameter <clameter@sgi.com>
Signed-off-by: Andy Whitcroft <apw@shadowen.org>
Acked-by: Mel Gorman <mel@csn.ul.ie>
Cc: Andi Kleen <ak@suse.de>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

2 files changed, 2 insertions, 0 deletions

diff --git a/include/asm-x86/page_64.h b/include/asm-x86/page_64.h
index 88adf1afb0a2..c3b52bcb171e 100644
--- a/include/asm-x86/page_64.h
+++ b/include/asm-x86/page_64.h
@@ -134,6 +134,7 @@ extern unsigned long __phys_addr(unsigned long);
          VM_READ | VM_WRITE | VM_MAYREAD | VM_MAYWRITE | VM_MAYEXEC)
 
 #define __HAVE_ARCH_GATE_AREA 1 
+#define vmemmap ((struct page *)VMEMMAP_START)
 
 #include <asm-generic/memory_model.h>
 #include <asm-generic/page.h>
diff --git a/include/asm-x86/pgtable_64.h b/include/asm-x86/pgtable_64.h
index 57dd6b3107ea..a79f5355e3b0 100644
--- a/include/asm-x86/pgtable_64.h
+++ b/include/asm-x86/pgtable_64.h
@@ -137,6 +137,7 @@ static inline pte_t ptep_get_and_clear_full(struct mm_struct *mm, unsigned long
 #define MAXMEM           _AC(0x3fffffffffff, UL)
 #define VMALLOC_START    _AC(0xffffc20000000000, UL)
 #define VMALLOC_END      _AC(0xffffe1ffffffffff, UL)
+#define VMEMMAP_START    _AC(0xffffe20000000000, UL)
 #define MODULES_VADDR    _AC(0xffffffff88000000, UL)
 #define MODULES_END      _AC(0xfffffffffff00000, UL)
 #define MODULES_LEN   (MODULES_END - MODULES_VADDR)