[PATCH 3/3] page-flags: hide PF_* validation check under separate config option

[Kirill A. Shutemov]

VM_BUG_ONs in PF_NO_TAIL() and PF_NO_COMPOUND() add 4+ KiB to
mm/build-in.o for DEBUG_VM kernel.

Let's hide them under new config option -- CONFIG_DEBUG_VM_PGFLAGS.
With the option enabled VM_BUG_ON_PGFLAGS() is equal to VM_BUG_ON_PAGE.

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
---
 include/linux/mmdebug.h    | 6 ++++++
 include/linux/page-flags.h | 8 +++-----
 lib/Kconfig.debug          | 8 ++++++++
 3 files changed, 17 insertions(+), 5 deletions(-)

diff --git a/include/linux/mmdebug.h b/include/linux/mmdebug.h
index 877ef226f90f..c447d8055e50 100644
--- a/include/linux/mmdebug.h
+++ b/include/linux/mmdebug.h
@@ -55,4 +55,10 @@ void dump_mm(const struct mm_struct *mm);
 #define VIRTUAL_BUG_ON(cond) do { } while (0)
 #endif
 
+#ifdef CONFIG_DEBUG_VM_PGFLAGS
+#define VM_BUG_ON_PGFLAGS(cond, page) VM_BUG_ON_PAGE(cond, page)
+#else
+#define VM_BUG_ON_PGFLAGS(cond, page) BUILD_BUG_ON_INVALID(cond)
+#endif
+
 #endif
diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h
index 19e4129f00e5..8d6e4e9a98af 100644
--- a/include/linux/page-flags.h
+++ b/include/linux/page-flags.h
@@ -153,12 +153,10 @@ enum pageflags {
 #define PF_ANY(page, enforce)	page
 #define PF_HEAD(page, enforce)	compound_head(page)
 #define PF_NO_TAIL(page, enforce) ({					\
-		if (enforce)						\
-			VM_BUG_ON_PAGE(PageTail(page), page);		\
+		VM_BUG_ON_PGFLAGS(enforce && PageTail(page), page);	\
 		compound_head(page);})
-#define PF_NO_COMPOUND(page, enforce) ({					\
-		if (enforce)						\
-			VM_BUG_ON_PAGE(PageCompound(page), page);	\
+#define PF_NO_COMPOUND(page, enforce) ({				\
+		VM_BUG_ON_PGFLAGS(enforce && PageCompound(page), page);	\
 		page;})
 
 /*
diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index e2894b23efb6..0d12bfa429de 100644
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -570,6 +570,14 @@ config DEBUG_VM_RB
 
 	  If unsure, say N.
 
+config DEBUG_VM_PGFLAGS
+	bool "Debug page-flags operations"
+	depends on DEBUG_VM
+	help
+	  Enables extra validation on page flags operations.
+
+	  If unsure, say N.
+
 config DEBUG_VIRTUAL
 	bool "Debug VM translations"
 	depends on DEBUG_KERNEL && X86
-- 
2.5.1

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