Require that the page lock is held, instead of the object lock, when

clearing the page's PGA_REFERENCED flag.  Since we are typically
manipulating the page's act_count field when we are clearing its
PGA_REFERENCED flag, the page lock is already held everywhere that we clear
the PGA_REFERENCED flag.  So, in fact, this revision only changes some
comments and an assertion.  Nonetheless, it will enable later changes to
object locking in the pageout code.

Introduce vm_page_assert_locked(), which completely hides the implementation
details of the page lock from the caller, and use it in
vm_page_aflag_clear().  (The existing vm_page_lock_assert() could not be
used in vm_page_aflag_clear().)  Over the coming weeks, I expect that we'll
either eliminate or replace the various uses of vm_page_lock_assert() with
vm_page_assert_locked().

Reviewed by:	attilio
Sponsored by:	EMC / Isilon Storage Division

2 files changed, 16 insertions, 7 deletions

diff --git a/sys/vm/vm_page.c b/sys/vm/vm_page.c
index 5a1c055..b6fbb93 100644
--- a/sys/vm/vm_page.c
+++ b/sys/vm/vm_page.c
@@ -2725,6 +2725,13 @@ vm_page_trylock_KBI(vm_page_t m, const char *file, int line)
 
 #if defined(INVARIANTS) || defined(INVARIANT_SUPPORT)
 void
+vm_page_assert_locked_KBI(vm_page_t m, const char *file, int line)
+{
+
+	vm_page_lock_assert_KBI(m, MA_OWNED, file, line);
+}
+
+void
 vm_page_lock_assert_KBI(vm_page_t m, int a, const char *file, int line)
 {
 
diff --git a/sys/vm/vm_page.h b/sys/vm/vm_page.h
index 6179a6d..c1d4b2a 100644
--- a/sys/vm/vm_page.h
+++ b/sys/vm/vm_page.h
@@ -229,9 +229,12 @@ extern struct mtx_padalign pa_lock[];
 #define	vm_page_trylock(m)	mtx_trylock(vm_page_lockptr((m)))
 #endif
 #if defined(INVARIANTS)
+#define	vm_page_assert_locked(m)		\
+    vm_page_assert_locked_KBI((m), __FILE__, __LINE__)
 #define	vm_page_lock_assert(m, a)		\
     vm_page_lock_assert_KBI((m), (a), __FILE__, __LINE__)
 #else
+#define	vm_page_assert_locked(m)
 #define	vm_page_lock_assert(m, a)
 #endif
 
@@ -240,10 +243,9 @@ extern struct mtx_padalign pa_lock[];
  * these flags, the functions vm_page_aflag_set() and vm_page_aflag_clear()
  * must be used.  Neither these flags nor these functions are part of the KBI.
  *
- * PGA_REFERENCED may be cleared only if the object containing the page is
- * locked.  It is set by both the MI and MD VM layers.  However, kernel
- * loadable modules should not directly set this flag.  They should call
- * vm_page_reference() instead.
+ * PGA_REFERENCED may be cleared only if the page is locked.  It is set by
+ * both the MI and MD VM layers.  However, kernel loadable modules should not
+ * directly set this flag.  They should call vm_page_reference() instead.
  *
  * PGA_WRITEABLE is set exclusively on managed pages by pmap_enter().  When it
  * does so, the page must be VPO_BUSY.  The MI VM layer must never access this
@@ -424,6 +426,7 @@ void vm_page_lock_KBI(vm_page_t m, const char *file, int line);
 void vm_page_unlock_KBI(vm_page_t m, const char *file, int line);
 int vm_page_trylock_KBI(vm_page_t m, const char *file, int line);
 #if defined(INVARIANTS) || defined(INVARIANT_SUPPORT)
+void vm_page_assert_locked_KBI(vm_page_t m, const char *file, int line);
 void vm_page_lock_assert_KBI(vm_page_t m, int a, const char *file, int line);
 #endif
 
@@ -451,11 +454,10 @@ vm_page_aflag_clear(vm_page_t m, uint8_t bits)
 	uint32_t *addr, val;
 
 	/*
-	 * The PGA_REFERENCED flag can only be cleared if the object
-	 * containing the page is locked.
+	 * The PGA_REFERENCED flag can only be cleared if the page is locked.
 	 */
 	if ((bits & PGA_REFERENCED) != 0)
-		VM_PAGE_OBJECT_LOCK_ASSERT(m);
+		vm_page_assert_locked(m);
 
 	/*
 	 * Access the whole 32-bit word containing the aflags field with an