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, 4 insertions, 3 deletions

diff --git a/sys/vm/vm_reserv.c b/sys/vm/vm_reserv.c
index e5ac1a5..98b0de2 100644
--- a/sys/vm/vm_reserv.c
+++ b/sys/vm/vm_reserv.c
@@ -47,6 +47,7 @@ __FBSDID("$FreeBSD$");
 #include <sys/malloc.h>
 #include <sys/mutex.h>
 #include <sys/queue.h>
+#include <sys/rwlock.h>
 #include <sys/sbuf.h>
 #include <sys/sysctl.h>
 #include <sys/systm.h>
@@ -311,7 +312,7 @@ vm_reserv_alloc_contig(vm_object_t object, vm_pindex_t pindex, u_long npages,
 	int i, index, n;
 
 	mtx_assert(&vm_page_queue_free_mtx, MA_OWNED);
-	VM_OBJECT_LOCK_ASSERT(object, MA_OWNED);
+	VM_OBJECT_ASSERT_WLOCKED(object);
 	KASSERT(npages != 0, ("vm_reserv_alloc_contig: npages is 0"));
 
 	/*
@@ -495,7 +496,7 @@ vm_reserv_alloc_page(vm_object_t object, vm_pindex_t pindex)
 	vm_reserv_t rv;
 
 	mtx_assert(&vm_page_queue_free_mtx, MA_OWNED);
-	VM_OBJECT_LOCK_ASSERT(object, MA_OWNED);
+	VM_OBJECT_ASSERT_WLOCKED(object);
 
 	/*
 	 * Is a reservation fundamentally impossible?
@@ -870,7 +871,7 @@ vm_reserv_rename(vm_page_t m, vm_object_t new_object, vm_object_t old_object,
 {
 	vm_reserv_t rv;
 
-	VM_OBJECT_LOCK_ASSERT(new_object, MA_OWNED);
+	VM_OBJECT_ASSERT_WLOCKED(new_object);
 	rv = vm_reserv_from_page(m);
 	if (rv->object == old_object) {
 		mtx_lock(&vm_page_queue_free_mtx);