3 files changed, 86 insertions, 1 deletions
diff --git a/include/linux/swap.h b/include/linux/swap.h
index 7e20b3016c7f..d0160265e3c5 100644
--- a/include/linux/swap.h
+++ b/include/linux/swap.h
@@ -11,7 +11,16 @@
 #define SWAP_FLAG_PRIO_MASK	0x7fff
 #define SWAP_FLAG_PRIO_SHIFT	0
 
-#define MAX_SWAPFILES 32
+/*
+ * MAX_SWAPFILES defines the maximum number of swaptypes: things which can
+ * be swapped to.  The swap type and the offset into that swap type are
+ * encoded into pte's and into pgoff_t's in the swapcache.  Using five bits
+ * for the type means that the maximum number of swapcache pages is 27 bits
+ * on 32-bit-pgoff_t architectures.  And that assumes that the architecture packs
+ * the type/offset into the pte as 5/27 as well.
+ */
+#define MAX_SWAPFILES_SHIFT	5
+#define MAX_SWAPFILES		(1 << MAX_SWAPFILES_SHIFT)
 
 /*
  * Magic header for a swap area. The first part of the union is
diff --git a/include/linux/swapops.h b/include/linux/swapops.h
new file mode 100644
index 000000000000..500f9960d939
--- /dev/null
+++ b/include/linux/swapops.h
@@ -0,0 +1,68 @@
+/*
+ * swapcache pages are stored in the swapper_space radix tree.  We want to
+ * get good packing density in that tree, so the index should be dense in
+ * the low-order bits.
+ *
+ * We arrange the `type' and `offset' fields so that `type' is at the five
+ * high-order bits of the smp_entry_t and `offset' is right-aligned in the
+ * remaining bits.
+ *
+ * swp_entry_t's are *never* stored anywhere in their arch-dependent format.
+ */
+#define SWP_TYPE_SHIFT(e)	(sizeof(e.val) * 8 - MAX_SWAPFILES_SHIFT)
+#define SWP_OFFSET_MASK(e)	((1 << SWP_TYPE_SHIFT(e)) - 1)
+
+/*
+ * Store a type+offset into a swp_entry_t in an arch-independent format
+ */
+static inline swp_entry_t swp_entry(unsigned type, pgoff_t offset)
+{
+	swp_entry_t ret;
+
+	ret.val = (type << SWP_TYPE_SHIFT(ret)) |
+			(offset & SWP_OFFSET_MASK(ret));
+	return ret;
+}
+
+/*
+ * Extract the `type' field from a swp_entry_t.  The swp_entry_t is in
+ * arch-independent format
+ */
+static inline unsigned swp_type(swp_entry_t entry)
+{
+	return (entry.val >> SWP_TYPE_SHIFT(entry)) &
+			((1 << MAX_SWAPFILES_SHIFT) - 1);
+}
+
+/*
+ * Extract the `offset' field from a swp_entry_t.  The swp_entry_t is in
+ * arch-independent format
+ */
+static inline pgoff_t swp_offset(swp_entry_t entry)
+{
+	return entry.val & SWP_OFFSET_MASK(entry);
+}
+
+/*
+ * Convert the arch-dependent pte representation of a swp_entry_t into an
+ * arch-independent swp_entry_t.
+ */
+static inline swp_entry_t pte_to_swp_entry(pte_t pte)
+{
+	swp_entry_t arch_entry;
+
+	arch_entry = __pte_to_swp_entry(pte);
+	return swp_entry(__swp_type(arch_entry), __swp_offset(arch_entry));
+}
+
+/*
+ * Convert the arch-independent representation of a swp_entry_t into the
+ * arch-dependent pte representation.
+ */
+static inline pte_t swp_entry_to_pte(swp_entry_t entry)
+{
+	swp_entry_t arch_entry;
+
+	arch_entry = __swp_entry(swp_type(entry), swp_offset(entry));
+	return __swp_entry_to_pte(arch_entry);
+}
diff --git a/include/linux/types.h b/include/linux/types.h
index 211461bc97c0..c102bcf8be83 100644
--- a/include/linux/types.h
+++ b/include/linux/types.h
@@ -124,6 +124,14 @@ typedef u64 sector_t;
 typedef unsigned long sector_t;
 #endif
 
+/*
+ * The type of an index into the pagecache.  Use a #define so asm/types.h
+ * can override it.
+ */
+#ifndef pgoff_t
+#define pgoff_t unsigned long
+#endif
+
 #endif /* __KERNEL_STRICT_NAMES */
 
 /*