[Cluster-devel] [PATCH 2/5] libgfs2: Use the correct parent for rgrp tree insertion

[Andrew Price <anprice@redhat.com>]

lgfs2_rgrps_append() was using the parent of the last rgrp instead of
the last rgrp itself as the intended parent when inserting new rgrps
into the tree. This left the tree unbalanced in such a way as to make
lookups of the last node in the tree effectively a linear list search.
This was done for each rgrp insertion so, although it didn't cause a
noticeable slow-down for smaller file sytems, tests on 250TB volumes
requiring over a million resource groups would become CPU bound and
could take hours to complete.

This patch fixes lgfs2_rgrps_append() to use the correct parent node for
rgrp tree insertions, giving a significant performance improvement when
creating file systems on large volumes.

Resolves: rhbz#1194446

Signed-off-by: Andrew Price <anprice@redhat.com>
---
 gfs2/libgfs2/rgrp.c | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/gfs2/libgfs2/rgrp.c b/gfs2/libgfs2/rgrp.c
index ed8e01d..cf4385a 100644
--- a/gfs2/libgfs2/rgrp.c
+++ b/gfs2/libgfs2/rgrp.c
@@ -539,9 +539,9 @@ struct osi_node *lgfs2_rgrps_root(lgfs2_rgrps_t rgs)
 lgfs2_rgrp_t lgfs2_rgrps_append(lgfs2_rgrps_t rgs, struct gfs2_rindex *entry)
 {
 	lgfs2_rgrp_t rg;
-	lgfs2_rgrp_t lastrg = (lgfs2_rgrp_t)osi_last(&rgs->root);
 	struct osi_node **link = &rgs->root.osi_node;
-	struct osi_node *parent = NULL;
+	struct osi_node *parent = osi_last(&rgs->root);
+	lgfs2_rgrp_t lastrg = (lgfs2_rgrp_t)parent;
 
 	errno = EINVAL;
 	if (entry == NULL)
@@ -550,7 +550,6 @@ lgfs2_rgrp_t lgfs2_rgrps_append(lgfs2_rgrps_t rgs, struct gfs2_rindex *entry)
 	if (lastrg != NULL) { /* Tree is not empty */
 		if (entry->ri_addr <= lastrg->ri.ri_addr)
 			return NULL; /* Appending with a lower address doesn't make sense */
-		parent = osi_parent(&lastrg->node);
 		link = &lastrg->node.osi_right;
 	}
 
-- 
1.9.3