x86: define _PAGE_NUMA by reusing software bits on the PMD and PTE levels

_PAGE_NUMA is currently an alias of _PROT_PROTNONE to trap NUMA hinting
faults on x86.  Care is taken such that _PAGE_NUMA is used only in
situations where the VMA flags distinguish between NUMA hinting faults
and prot_none faults.  This decision was x86-specific and conceptually
it is difficult requiring special casing to distinguish between PROTNONE
and NUMA ptes based on context.

Fundamentally, we only need the _PAGE_NUMA bit to tell the difference
between an entry that is really unmapped and a page that is protected
for NUMA hinting faults as if the PTE is not present then a fault will
be trapped.

Swap PTEs on x86-64 use the bits after _PAGE_GLOBAL for the offset.
This patch shrinks the maximum possible swap size and uses the bit to
uniquely distinguish between NUMA hinting ptes and swap ptes.

Signed-off-by: Mel Gorman <mgorman@suse.de>
Cc: David Vrabel <david.vrabel@citrix.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Peter Anvin <hpa@zytor.com>
Cc: Fengguang Wu <fengguang.wu@intel.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Steven Noonan <steven@uplinklabs.net>
Cc: Rik van Riel <riel@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Dave Hansen <dave.hansen@intel.com>
Cc: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
Cc: Cyrill Gorcunov <gorcunov@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 6 insertions, 2 deletions

diff --git a/include/asm-generic/pgtable.h b/include/asm-generic/pgtable.h
index a8015a7a55bb..53b2acc38213 100644
--- a/include/asm-generic/pgtable.h
+++ b/include/asm-generic/pgtable.h
@@ -233,6 +233,10 @@ static inline int pmd_same(pmd_t pmd_a, pmd_t pmd_b)
 # define pte_accessible(mm, pte)	((void)(pte), 1)
 #endif
 
+#ifndef pte_present_nonuma
+#define pte_present_nonuma(pte) pte_present(pte)
+#endif
+
 #ifndef flush_tlb_fix_spurious_fault
 #define flush_tlb_fix_spurious_fault(vma, address) flush_tlb_page(vma, address)
 #endif
@@ -670,7 +674,7 @@ static inline int pmd_trans_unstable(pmd_t *pmd)
 static inline int pte_numa(pte_t pte)
 {
 	return (pte_flags(pte) &
-		(_PAGE_NUMA|_PAGE_PRESENT)) == _PAGE_NUMA;
+		(_PAGE_NUMA|_PAGE_PROTNONE|_PAGE_PRESENT)) == _PAGE_NUMA;
 }
 #endif
 
@@ -678,7 +682,7 @@ static inline int pte_numa(pte_t pte)
 static inline int pmd_numa(pmd_t pmd)
 {
 	return (pmd_flags(pmd) &
-		(_PAGE_NUMA|_PAGE_PRESENT)) == _PAGE_NUMA;
+		(_PAGE_NUMA|_PAGE_PROTNONE|_PAGE_PRESENT)) == _PAGE_NUMA;
 }
 #endif