FreeBSD: retire z_nr_znodes

This is a step towards retiring the z_all_znodes list, which is
redundant to per-mount point list already maintained by the kernel.

The lock protecting z_all_znodes is amongst top of the profile when
running parallel scans of the filesystem with find(1).

Signed-off-by: Mateusz Guzik <mjguzik@gmail.com>

include/os/freebsd/zfs/sys/zfs_vfsops_os.h

@@ -93,7 +93,6 @@ struct zfsvfs {
 	zfs_teardown_lock_t z_teardown_lock;
 	zfs_teardown_inactive_lock_t z_teardown_inactive_lock;
 	list_t		z_all_znodes;	/* all vnodes in the fs */
-	uint64_t	z_nr_znodes;	/* number of znodes in the fs */
 	kmutex_t	z_znodes_lock;	/* lock for z_all_znodes */
 	struct zfsctl_root	*z_ctldir;	/* .zfs directory pointer */
 	boolean_t	z_show_ctldir;	/* expose .zfs in the root dir */

module/os/freebsd/zfs/zfs_vfsops.c

@@ -1154,7 +1154,6 @@ zfsvfs_free(zfsvfs_t *zfsvfs)
 
 	mutex_destroy(&zfsvfs->z_znodes_lock);
 	mutex_destroy(&zfsvfs->z_lock);
-	ASSERT3U(zfsvfs->z_nr_znodes, ==, 0);
 	list_destroy(&zfsvfs->z_all_znodes);
 	ZFS_TEARDOWN_DESTROY(zfsvfs);
 	ZFS_TEARDOWN_INACTIVE_DESTROY(zfsvfs);
@@ -1558,12 +1557,11 @@ zfsvfs_teardown(zfsvfs_t *zfsvfs, boolean_t unmounting)
 		 * may add the parents of dir-based xattrs to the taskq
 		 * so we want to wait for these.
 		 *
-		 * We can safely read z_nr_znodes without locking because the
-		 * VFS has already blocked operations which add to the
-		 * z_all_znodes list and thus increment z_nr_znodes.
+		 * We can safely check z_all_znodes for being empty because the
+		 * VFS has already blocked operations which add to it.
 		 */
 		int round = 0;
-		while (zfsvfs->z_nr_znodes > 0) {
+		while (!list_is_empty(&zfsvfs->z_all_znodes)) {
 			taskq_wait_outstanding(dsl_pool_zrele_taskq(
 			    dmu_objset_pool(zfsvfs->z_os)), 0);
 			if (++round > 1 && !unmounting)

module/os/freebsd/zfs/zfs_znode.c

@@ -537,7 +537,6 @@ zfs_znode_alloc(zfsvfs_t *zfsvfs, dmu_buf_t *db, int blksz,
 
 	mutex_enter(&zfsvfs->z_znodes_lock);
 	list_insert_tail(&zfsvfs->z_all_znodes, zp);
-	zfsvfs->z_nr_znodes++;
 	zp->z_zfsvfs = zfsvfs;
 	mutex_exit(&zfsvfs->z_znodes_lock);
 
@@ -1286,7 +1285,6 @@ zfs_znode_free(znode_t *zp)
 	mutex_enter(&zfsvfs->z_znodes_lock);
 	POINTER_INVALIDATE(&zp->z_zfsvfs);
 	list_remove(&zfsvfs->z_all_znodes, zp);
-	zfsvfs->z_nr_znodes--;
 	mutex_exit(&zfsvfs->z_znodes_lock);
 
 #if __FreeBSD_version >= 1300139