From: jbeulich@xxxxxxxxxx
Subject: allow use of split page table lock in non-debug case
Patch-mainline: obsolete

Index: head-2007-02-27/include/linux/mm.h
===================================================================
--- head-2007-02-27.orig/include/linux/mm.h	2007-02-27 16:25:00.000000000 +0100
+++ head-2007-02-27/include/linux/mm.h	2007-02-28 17:11:56.000000000 +0100
@@ -891,7 +891,11 @@ static inline pmd_t *pmd_alloc(struct mm
 #define pte_lock_init(_page)	do {					\
 	spin_lock_init(__pte_lockptr(_page));				\
 } while (0)
-#define pte_lock_deinit(page)	((page)->mapping = NULL)
+#define pte_lock_deinit(_page)	do {					\
+	if ((void *)&((struct page *)0)->mapping			\
+	    < (void *)(__pte_lockptr((struct page *)0) + 1))		\
+		(_page)->mapping = NULL;				\
+} while (0)
 #define pte_lockptr(mm, pmd)	({(void)(mm); __pte_lockptr(pmd_page(*(pmd)));})
 #else
 /*
Index: head-2007-02-27/include/linux/page-flags.h
===================================================================
--- head-2007-02-27.orig/include/linux/page-flags.h	2007-02-27 16:26:22.000000000 +0100
+++ head-2007-02-27/include/linux/page-flags.h	2007-02-28 16:38:41.000000000 +0100
@@ -254,8 +254,16 @@ static inline void SetPageUptodate(struc
 #define ClearPageUncached(page)	clear_bit(PG_uncached, &(page)->flags)
 
 #define PageForeign(page)	test_bit(PG_foreign, &(page)->flags)
+#if NR_CPUS >= CONFIG_SPLIT_PTLOCK_CPUS
+#define PageForeignCheck()						\
+	BUILD_BUG_ON((void *)&((struct page *)0)->mapping		\
+	             < (void *)(__pte_lockptr((struct page *)0) + 1))
+#else
+#define PageForeignCheck() ((void)0)
+#endif
 #define SetPageForeign(page, dtor) do {		\
 	set_bit(PG_foreign, &(page)->flags);	\
+	PageForeignCheck();			\
 	(page)->mapping = (void *)dtor;		\
 } while (0)
 #define ClearPageForeign(page) do {		\
Index: head-2007-02-27/mm/Kconfig
===================================================================
--- head-2007-02-27.orig/mm/Kconfig	2007-02-27 16:23:14.000000000 +0100
+++ head-2007-02-27/mm/Kconfig	2007-02-28 16:26:48.000000000 +0100
@@ -139,7 +139,8 @@ config SPLIT_PTLOCK_CPUS
 	int
 	default "4096" if ARM && !CPU_CACHE_VIPT
 	default "4096" if PARISC && !PA20
-	default "4096" if X86_XEN || X86_64_XEN
+	default "4096" if X86_XEN && (PREEMPT || DEBUG_SPINLOCK || DEBUG_LOCK_ALLOC)
+	default "4096" if X86_64_XEN && (DEBUG_SPINLOCK || DEBUG_LOCK_ALLOC)
 	default "4"
 
 #