[GFS2] Use slab operations for all gfs2_bufdata allocations

The old revoke structure was allocated using kalloc/kfree but
there is a slab cache for gfs2_bufdata, so we should use that
now that the structures have been converted.

This is part two of the patch series to merge the revoke
and gfs2_bufdata structures.
Signed-off-by: Steven Whitehouse <swhiteho@redhat.com>

fs/gfs2/lops.c

@@ -393,7 +393,7 @@ static void revoke_lo_before_commit(struct gfs2_sbd *sdp)
 		}
 
 		*(__be64 *)(bh->b_data + offset) = cpu_to_be64(bd->bd_blkno);
-		kfree(bd);
+		kmem_cache_free(gfs2_bufdata_cachep, bd);
 
 		offset += sizeof(u64);
 	}

fs/gfs2/trans.c

@@ -144,7 +144,7 @@ void gfs2_trans_add_bh(struct gfs2_glock *gl, struct buffer_head *bh, int meta)
 
 void gfs2_trans_add_revoke(struct gfs2_sbd *sdp, u64 blkno)
 {
-	struct gfs2_bufdata *bd = kmalloc(sizeof(struct gfs2_bufdata),
+	struct gfs2_bufdata *bd = kmem_cache_alloc(gfs2_bufdata_cachep,
 					  GFP_NOFS | __GFP_NOFAIL);
 	lops_init_le(&bd->bd_le, &gfs2_revoke_lops);
 	bd->bd_blkno = blkno;
@@ -172,7 +172,7 @@ void gfs2_trans_add_unrevoke(struct gfs2_sbd *sdp, u64 blkno)
 
 	if (found) {
 		struct gfs2_trans *tr = current->journal_info;
-		kfree(bd);
+		kmem_cache_free(gfs2_bufdata_cachep, bd);
 		tr->tr_num_revoke_rm++;
 	}
 }