mm: save soft-dirty bits on swapped pages

[cascardo/linux.git] / arch / x86 / include / asm / pgtable_types.h

diff --git a/arch/x86/include/asm/pgtable_types.h b/arch/x86/include/asm/pgtable_types.h
index c98ac63..5e8442f 100644 (file)
--- a/arch/x86/include/asm/pgtable_types.h
+++ b/arch/x86/include/asm/pgtable_types.h
@@ -67,6 +67,19 @@
 #define _PAGE_SOFT_DIRTY       (_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
+ * into swap entry computation, but bit 6 is used for nonlinear
+ * file mapping, so we borrow bit 7 for soft dirty tracking.
+ */
+#ifdef CONFIG_MEM_SOFT_DIRTY
+#define _PAGE_SWP_SOFT_DIRTY   _PAGE_PSE
+#else
+#define _PAGE_SWP_SOFT_DIRTY   (_AT(pteval_t, 0))
+#endif
+
 #if defined(CONFIG_X86_64) || defined(CONFIG_X86_PAE)
 #define _PAGE_NX       (_AT(pteval_t, 1) << _PAGE_BIT_NX)
 #else