1 files changed, 69 insertions, 0 deletions
diff --git a/include/linux/swapops.h b/include/linux/swapops.h
new file mode 100644
index 000000000000..d4c7db35e708
--- /dev/null
+++ b/include/linux/swapops.h
@@ -0,0 +1,69 @@
+/*
+ * 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)	((1UL << 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 long 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));
+}
+
+/*
+ * 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;
+
+	BUG_ON(pte_file(pte));
+	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));
+	BUG_ON(pte_file(__swp_entry_to_pte(arch_entry)));
+	return __swp_entry_to_pte(arch_entry);
+}