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, 35 insertions, 31 deletions

diff --git a/arch/x86/include/asm/pgtable_types.h b/arch/x86/include/asm/pgtable_types.h
index eb3d449451336..f216963760e51 100644
--- a/arch/x86/include/asm/pgtable_types.h
+++ b/arch/x86/include/asm/pgtable_types.h
@@ -16,15 +16,26 @@
 #define _PAGE_BIT_PSE		7	/* 4 MB (or 2MB) page */
 #define _PAGE_BIT_PAT		7	/* on 4KB pages */
 #define _PAGE_BIT_GLOBAL	8	/* Global TLB entry PPro+ */
-#define _PAGE_BIT_UNUSED1	9	/* available for programmer */
-#define _PAGE_BIT_IOMAP		10	/* flag used to indicate IO mapping */
-#define _PAGE_BIT_HIDDEN	11	/* hidden by kmemcheck */
+#define _PAGE_BIT_SOFTW1	9	/* available for programmer */
+#define _PAGE_BIT_SOFTW2	10	/* " */
+#define _PAGE_BIT_SOFTW3	11	/* " */
 #define _PAGE_BIT_PAT_LARGE	12	/* On 2MB or 1GB pages */
-#define _PAGE_BIT_SPECIAL	_PAGE_BIT_UNUSED1
-#define _PAGE_BIT_CPA_TEST	_PAGE_BIT_UNUSED1
-#define _PAGE_BIT_SPLITTING	_PAGE_BIT_UNUSED1 /* only valid on a PSE pmd */
+#define _PAGE_BIT_SPECIAL	_PAGE_BIT_SOFTW1
+#define _PAGE_BIT_CPA_TEST	_PAGE_BIT_SOFTW1
+#define _PAGE_BIT_SPLITTING	_PAGE_BIT_SOFTW2 /* only valid on a PSE pmd */
+#define _PAGE_BIT_IOMAP		_PAGE_BIT_SOFTW2 /* flag used to indicate IO mapping */
+#define _PAGE_BIT_HIDDEN	_PAGE_BIT_SOFTW3 /* hidden by kmemcheck */
+#define _PAGE_BIT_SOFT_DIRTY	_PAGE_BIT_SOFTW3 /* software dirty tracking */
 #define _PAGE_BIT_NX           63       /* No execute: only valid after cpuid check */
 
+/*
+ * Swap offsets on configurations that allow automatic NUMA balancing use the
+ * bits after _PAGE_BIT_GLOBAL. To uniquely distinguish NUMA hinting PTEs from
+ * swap entries, we use the first bit after _PAGE_BIT_GLOBAL and shrink the
+ * maximum possible swap space from 16TB to 8TB.
+ */
+#define _PAGE_BIT_NUMA		(_PAGE_BIT_GLOBAL+1)
+
 /* If _PAGE_BIT_PRESENT is clear, we use these: */
 /* - if the user mapped it with PROT_NONE; pte_present gives true */
 #define _PAGE_BIT_PROTNONE	_PAGE_BIT_GLOBAL
@@ -40,7 +51,7 @@
 #define _PAGE_DIRTY	(_AT(pteval_t, 1) << _PAGE_BIT_DIRTY)
 #define _PAGE_PSE	(_AT(pteval_t, 1) << _PAGE_BIT_PSE)
 #define _PAGE_GLOBAL	(_AT(pteval_t, 1) << _PAGE_BIT_GLOBAL)
-#define _PAGE_UNUSED1	(_AT(pteval_t, 1) << _PAGE_BIT_UNUSED1)
+#define _PAGE_SOFTW1	(_AT(pteval_t, 1) << _PAGE_BIT_SOFTW1)
 #define _PAGE_IOMAP	(_AT(pteval_t, 1) << _PAGE_BIT_IOMAP)
 #define _PAGE_PAT	(_AT(pteval_t, 1) << _PAGE_BIT_PAT)
 #define _PAGE_PAT_LARGE (_AT(pteval_t, 1) << _PAGE_BIT_PAT_LARGE)
@@ -61,8 +72,6 @@
  * they do not conflict with each other.
  */
 
-#define _PAGE_BIT_SOFT_DIRTY	_PAGE_BIT_HIDDEN
-
 #ifdef CONFIG_MEM_SOFT_DIRTY
 #define _PAGE_SOFT_DIRTY	(_AT(pteval_t, 1) << _PAGE_BIT_SOFT_DIRTY)
 #else
@@ -70,6 +79,21 @@
 #endif
 
 /*
+ * _PAGE_NUMA distinguishes between a numa hinting minor fault and a page
+ * that is not present. The hinting fault gathers numa placement statistics
+ * (see pte_numa()). The bit is always zero when the PTE is not present.
+ *
+ * The bit picked must be always zero when the pmd is present and not
+ * present, so that we don't lose information when we set it while
+ * atomically clearing the present bit.
+ */
+#ifdef CONFIG_NUMA_BALANCING
+#define _PAGE_NUMA	(_AT(pteval_t, 1) << _PAGE_BIT_NUMA)
+#else
+#define _PAGE_NUMA	(_AT(pteval_t, 0))
+#endif
+
+/*
  * Tracking soft dirty bit when a page goes to a swap is tricky.
  * We need a bit which can be stored in pte _and_ not conflict
  * with swap entry format. On x86 bits 6 and 7 are *not* involved
@@ -94,26 +118,6 @@
 #define _PAGE_FILE	(_AT(pteval_t, 1) << _PAGE_BIT_FILE)
 #define _PAGE_PROTNONE	(_AT(pteval_t, 1) << _PAGE_BIT_PROTNONE)
 
-/*
- * _PAGE_NUMA indicates that this page will trigger a numa hinting
- * minor page fault to gather numa placement statistics (see
- * pte_numa()). The bit picked (8) is within the range between
- * _PAGE_FILE (6) and _PAGE_PROTNONE (8) bits. Therefore, it doesn't
- * require changes to the swp entry format because that bit is always
- * zero when the pte is not present.
- *
- * The bit picked must be always zero when the pmd is present and not
- * present, so that we don't lose information when we set it while
- * atomically clearing the present bit.
- *
- * Because we shared the same bit (8) with _PAGE_PROTNONE this can be
- * interpreted as _PAGE_NUMA only in places that _PAGE_PROTNONE
- * couldn't reach, like handle_mm_fault() (see access_error in
- * arch/x86/mm/fault.c, the vma protection must not be PROT_NONE for
- * handle_mm_fault() to be invoked).
- */
-#define _PAGE_NUMA	_PAGE_PROTNONE
-
 #define _PAGE_TABLE	(_PAGE_PRESENT | _PAGE_RW | _PAGE_USER |	\
 			 _PAGE_ACCESSED | _PAGE_DIRTY)
 #define _KERNPG_TABLE	(_PAGE_PRESENT | _PAGE_RW | _PAGE_ACCESSED |	\
@@ -122,8 +126,8 @@
 /* Set of bits not changed in pte_modify */
 #define _PAGE_CHG_MASK	(PTE_PFN_MASK | _PAGE_PCD | _PAGE_PWT |		\
 			 _PAGE_SPECIAL | _PAGE_ACCESSED | _PAGE_DIRTY |	\
-			 _PAGE_SOFT_DIRTY)
-#define _HPAGE_CHG_MASK (_PAGE_CHG_MASK | _PAGE_PSE)
+			 _PAGE_SOFT_DIRTY | _PAGE_NUMA)
+#define _HPAGE_CHG_MASK (_PAGE_CHG_MASK | _PAGE_PSE | _PAGE_NUMA)
 
 #define _PAGE_CACHE_MASK	(_PAGE_PCD | _PAGE_PWT)
 #define _PAGE_CACHE_WB		(0)