GFS2: Make resource groups "append only" during life of fs

Since we have ruled out supporting online filesystem shrink,
it is possible to make the resource group list append only
during the life of a super block. This gives several benefits:

Firstly, we only need to read new rindex elements as they are added
rather than needing to reread the whole rindex file each time one
element is added.

Secondly, the rindex glock can be held for much shorter periods of
time, and is completely removed from the fast path for allocations.
The lock is taken in shared mode only when updating the resource
groups when the first allocation occurs, and after a grow has
taken place.

Thirdly, this results in a reduction in code size, and everything
gets a lot simpler to understand in this area.

Signed-off-by: Steven Whitehouse <swhiteho@redhat.com>

fs/gfs2/glops.c

@@ -134,8 +134,7 @@ void gfs2_ail_flush(struct gfs2_glock *gl)
 static void rgrp_go_sync(struct gfs2_glock *gl)
 {
 	struct address_space *metamapping = gfs2_glock2aspace(gl);
-	struct gfs2_rgrpd *rgd = gl->gl_object;
-	unsigned int x;
+	struct gfs2_rgrpd *rgd;
 	int error;
 
 	if (!test_and_clear_bit(GLF_DIRTY, &gl->gl_flags))
@@ -148,14 +147,11 @@ static void rgrp_go_sync(struct gfs2_glock *gl)
         mapping_set_error(metamapping, error);
 	gfs2_ail_empty_gl(gl);
 
-	if (!rgd)
-		return;
-
-	for (x = 0; x < rgd->rd_length; x++) {
-		struct gfs2_bitmap *bi = rgd->rd_bits + x;
-		kfree(bi->bi_clone);
-		bi->bi_clone = NULL;
-	}
+	spin_lock(&gl->gl_spin);
+	rgd = gl->gl_object;
+	if (rgd)
+		gfs2_free_clones(rgd);
+	spin_unlock(&gl->gl_spin);
 }
 
 /**