Switch the vm_object mutex to be a rwlock. This will enable in the

future further optimizations where the vm_object lock will be held
in read mode most of the time the page cache resident pool of pages
are accessed for reading purposes.

The change is mostly mechanical but few notes are reported:
* The KPI changes as follow:
  - VM_OBJECT_LOCK() -> VM_OBJECT_WLOCK()
  - VM_OBJECT_TRYLOCK() -> VM_OBJECT_TRYWLOCK()
  - VM_OBJECT_UNLOCK() -> VM_OBJECT_WUNLOCK()
  - VM_OBJECT_LOCK_ASSERT(MA_OWNED) -> VM_OBJECT_ASSERT_WLOCKED()
    (in order to avoid visibility of implementation details)
  - The read-mode operations are added:
    VM_OBJECT_RLOCK(), VM_OBJECT_TRYRLOCK(), VM_OBJECT_RUNLOCK(),
    VM_OBJECT_ASSERT_RLOCKED(), VM_OBJECT_ASSERT_LOCKED()
* The vm/vm_pager.h namespace pollution avoidance (forcing requiring
  sys/mutex.h in consumers directly to cater its inlining functions
  using VM_OBJECT_LOCK()) imposes that all the vm/vm_pager.h
  consumers now must include also sys/rwlock.h.
* zfs requires a quite convoluted fix to include FreeBSD rwlocks into
  the compat layer because the name clash between FreeBSD and solaris
  versions must be avoided.
  At this purpose zfs redefines the vm_object locking functions
  directly, isolating the FreeBSD components in specific compat stubs.

The KPI results heavilly broken by this commit.  Thirdy part ports must
be updated accordingly (I can think off-hand of VirtualBox, for example).

Sponsored by:	EMC / Isilon storage division
Reviewed by:	jeff
Reviewed by:	pjd (ZFS specific review)
Discussed with:	alc
Tested by:	pho

1 files changed, 25 insertions, 12 deletions

diff --git a/sys/vm/vm_object.h b/sys/vm/vm_object.h
index 319324f..dac90fc 100644
--- a/sys/vm/vm_object.h
+++ b/sys/vm/vm_object.h
@@ -70,15 +70,16 @@
 #include <sys/queue.h>
 #include <sys/_lock.h>
 #include <sys/_mutex.h>
+#include <sys/_rwlock.h>
 
 /*
  *	Types defined:
  *
  *	vm_object_t		Virtual memory object.
  *
- *	The root of cached pages pool is protected by both the per-object mutex
+ *	The root of cached pages pool is protected by both the per-object lock
  *	and the free pages queue mutex.
- *	On insert in the cache splay tree, the per-object mutex is expected
+ *	On insert in the cache splay tree, the per-object lock is expected
  *	to be already held and the free pages queue mutex will be
  *	acquired during the operation too.
  *	On remove and lookup from the cache splay tree, only the free
@@ -89,13 +90,13 @@
  *
  * List of locks
  *	(c)	const until freed
- *	(o)	per-object mutex
+ *	(o)	per-object lock 
  *	(f)	free pages queue mutex
  *
  */
 
 struct vm_object {
-	struct mtx mtx;
+	struct rwlock lock;
 	TAILQ_ENTRY(vm_object) object_list; /* list of all objects */
 	LIST_HEAD(, vm_object) shadow_head; /* objects that this is a shadow for */
 	LIST_ENTRY(vm_object) shadow_list; /* chain of shadow objects */
@@ -203,14 +204,26 @@ extern struct vm_object kmem_object_store;
 #define	kernel_object	(&kernel_object_store)
 #define	kmem_object	(&kmem_object_store)
 
-#define	VM_OBJECT_LOCK(object)		mtx_lock(&(object)->mtx)
-#define	VM_OBJECT_LOCK_ASSERT(object, type) \
-					mtx_assert(&(object)->mtx, (type))
-#define	VM_OBJECT_SLEEP(object, wchan, pri, wmesg, timo) \
-					msleep((wchan), &(object)->mtx, (pri), \
-					    (wmesg), (timo))
-#define	VM_OBJECT_TRYLOCK(object)	mtx_trylock(&(object)->mtx)
-#define	VM_OBJECT_UNLOCK(object)	mtx_unlock(&(object)->mtx)
+#define	VM_OBJECT_ASSERT_LOCKED(object)					\
+	rw_assert(&(object)->lock, RA_LOCKED)
+#define	VM_OBJECT_ASSERT_RLOCKED(object)				\
+	rw_assert(&(object)->lock, RA_RLOCKED)
+#define	VM_OBJECT_ASSERT_WLOCKED(object)				\
+	rw_assert(&(object)->lock, RA_WLOCKED)
+#define	VM_OBJECT_RLOCK(object)						\
+	rw_rlock(&(object)->lock)
+#define	VM_OBJECT_RUNLOCK(object)					\
+	rw_runlock(&(object)->lock)
+#define	VM_OBJECT_SLEEP(object, wchan, pri, wmesg, timo)		\
+	rw_sleep((wchan), &(object)->lock, (pri), (wmesg), (timo))
+#define	VM_OBJECT_TRYRLOCK(object)					\
+	rw_try_rlock(&(object)->lock)
+#define	VM_OBJECT_TRYWLOCK(object)					\
+	rw_try_wlock(&(object)->lock)
+#define	VM_OBJECT_WLOCK(object)						\
+	rw_wlock(&(object)->lock)
+#define	VM_OBJECT_WUNLOCK(object)					\
+	rw_wunlock(&(object)->lock)
 
 /*
  *	The object must be locked or thread private.