ocfs2: allocation hints

Record the most recently used allocation group on the allocation context, so
that subsequent allocations can attempt to optimize for contiguousness.
Local alloc especially should benefit from this as the current chain search
tends to let it spew across the disk.

Signed-off-by: Mark Fasheh <mark.fasheh@oracle.com>

fs/ocfs2/localalloc.c

@@ -840,6 +840,12 @@ static int ocfs2_local_alloc_new_window(struct ocfs2_super *osb,
 
 	mlog(0, "Allocating %u clusters for a new window.\n",
 	     ocfs2_local_alloc_window_bits(osb));
+
+	/* Instruct the allocation code to try the most recently used
+	 * cluster group. We'll re-record the group used this pass
+	 * below. */
+	ac->ac_last_group = osb->la_last_gd;
+
 	/* we used the generic suballoc reserve function, but we set
 	 * everything up nicely, so there's no reason why we can't use
 	 * the more specific cluster api to claim bits. */
@@ -852,6 +858,8 @@ static int ocfs2_local_alloc_new_window(struct ocfs2_super *osb,
 		goto bail;
 	}
 
+	osb->la_last_gd = ac->ac_last_group;
+
 	la->la_bm_off = cpu_to_le32(cluster_off);
 	alloc->id1.bitmap1.i_total = cpu_to_le32(cluster_count);
 	/* just in case... In the future when we find space ourselves,