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/super.c

@@ -1037,7 +1037,6 @@ static int statfs_slow_fill(struct gfs2_rgrpd *rgd,
 
 static int gfs2_statfs_slow(struct gfs2_sbd *sdp, struct gfs2_statfs_change_host *sc)
 {
-	struct gfs2_holder ri_gh;
 	struct gfs2_rgrpd *rgd_next;
 	struct gfs2_holder *gha, *gh;
 	unsigned int slots = 64;
@@ -1050,10 +1049,6 @@ static int gfs2_statfs_slow(struct gfs2_sbd *sdp, struct gfs2_statfs_change_host
 	if (!gha)
 		return -ENOMEM;
 
-	error = gfs2_rindex_hold(sdp, &ri_gh);
-	if (error)
-		goto out;
-
 	rgd_next = gfs2_rgrpd_get_first(sdp);
 
 	for (;;) {
@@ -1096,9 +1091,6 @@ static int gfs2_statfs_slow(struct gfs2_sbd *sdp, struct gfs2_statfs_change_host
 		yield();
 	}
 
-	gfs2_glock_dq_uninit(&ri_gh);
-
-out:
 	kfree(gha);
 	return error;
 }
@@ -1150,6 +1142,10 @@ static int gfs2_statfs(struct dentry *dentry, struct kstatfs *buf)
 	struct gfs2_statfs_change_host sc;
 	int error;
 
+	error = gfs2_rindex_update(sdp);
+	if (error)
+		return error;
+
 	if (gfs2_tune_get(sdp, gt_statfs_slow))
 		error = gfs2_statfs_slow(sdp, &sc);
 	else
@@ -1420,21 +1416,17 @@ static int gfs2_dinode_dealloc(struct gfs2_inode *ip)
 	if (error)
 		goto out;
 
-	error = gfs2_rindex_hold(sdp, &al->al_ri_gh);
-	if (error)
-		goto out_qs;
-
 	rgd = gfs2_blk2rgrpd(sdp, ip->i_no_addr);
 	if (!rgd) {
 		gfs2_consist_inode(ip);
 		error = -EIO;
-		goto out_rindex_relse;
+		goto out_qs;
 	}
 
 	error = gfs2_glock_nq_init(rgd->rd_gl, LM_ST_EXCLUSIVE, 0,
 				   &al->al_rgd_gh);
 	if (error)
-		goto out_rindex_relse;
+		goto out_qs;
 
 	error = gfs2_trans_begin(sdp, RES_RG_BIT + RES_STATFS + RES_QUOTA,
 				 sdp->sd_jdesc->jd_blocks);
@@ -1449,8 +1441,6 @@ static int gfs2_dinode_dealloc(struct gfs2_inode *ip)
 
 out_rg_gunlock:
 	gfs2_glock_dq_uninit(&al->al_rgd_gh);
-out_rindex_relse:
-	gfs2_glock_dq_uninit(&al->al_ri_gh);
 out_qs:
 	gfs2_quota_unhold(ip);
 out: