Back out the modification of vm_map locks from lockmgr to sx locks. The

best path forward now is likely to change the lockmgr locks to simple
sleep mutexes, then see if any extra contention it generates is greater
than removed overhead of managing local locking state information,
cost of extra calls into lockmgr, etc.

Additionally, making the vm_map lock a mutex and respecting it properly
will put us much closer to not needing Giant magic in vm.

1 files changed, 10 insertions, 16 deletions

diff --git a/sys/vm/vm_fault.c b/sys/vm/vm_fault.c
index 02a7f46..051e48e 100644
--- a/sys/vm/vm_fault.c
+++ b/sys/vm/vm_fault.c
@@ -111,11 +111,7 @@ struct faultstate {
 	vm_pindex_t first_pindex;
 	vm_map_t map;
 	vm_map_entry_t entry;
-	enum {
-		LSV_FALSE,	/* the lookup's lock has been dropped */
-		LSV_TRUE,	/* the lookup's lock is still valid */
-		LSV_UPGRADED	/* the lookup's lock is now exclusive */
-	} lookup_still_valid;
+	int lookup_still_valid;
 	struct vnode *vp;
 };
 
@@ -130,11 +126,9 @@ release_page(struct faultstate *fs)
 static __inline void
 unlock_map(struct faultstate *fs)
 {
-	if (fs->lookup_still_valid != LSV_FALSE) {
-		if (fs->lookup_still_valid == LSV_UPGRADED)
-			vm_map_lock_downgrade(fs->map);
+	if (fs->lookup_still_valid) {
 		vm_map_lookup_done(fs->map, fs->entry);
-		fs->lookup_still_valid = LSV_FALSE;
+		fs->lookup_still_valid = FALSE;
 	}
 }
 
@@ -288,7 +282,7 @@ RetryFault:;
 			fs.first_pindex, fs.first_pindex + 1);
 	}
 
-	fs.lookup_still_valid = LSV_TRUE;
+	fs.lookup_still_valid = TRUE;
 
 	if (wired)
 		fault_type = prot;
@@ -662,11 +656,11 @@ readrest:
 				/*
 				 * grab the lock if we need to
 				 */
-				(fs.lookup_still_valid != LSV_FALSE ||
-				 vm_map_try_lock(fs.map) == 0)
+				(fs.lookup_still_valid ||
+				 lockmgr(&fs.map->lock, LK_EXCLUSIVE|LK_NOWAIT, (void *)0, curthread) == 0)
 			    ) {
-				if (fs.lookup_still_valid == LSV_FALSE)
-					fs.lookup_still_valid = LSV_UPGRADED;
+				
+				fs.lookup_still_valid = 1;
 				/*
 				 * get rid of the unnecessary page
 				 */
@@ -721,7 +715,7 @@ readrest:
 	 * We must verify that the maps have not changed since our last
 	 * lookup.
 	 */
-	if (fs.lookup_still_valid == LSV_FALSE &&
+	if (!fs.lookup_still_valid &&
 		(fs.map->timestamp != map_generation)) {
 		vm_object_t retry_object;
 		vm_pindex_t retry_pindex;
@@ -770,7 +764,7 @@ readrest:
 			unlock_and_deallocate(&fs);
 			return (result);
 		}
-		fs.lookup_still_valid = LSV_TRUE;
+		fs.lookup_still_valid = TRUE;
 
 		if ((retry_object != fs.first_object) ||
 		    (retry_pindex != fs.first_pindex)) {