Btrfs: faster and more efficient extent map insertion

Before this change, adding an extent map to the extent map tree of an
inode required 2 tree nevigations:

1) doing a tree navigation to search for an existing extent map starting
   at the same offset or an extent map that overlaps the extent map we
   want to insert;

2) Another tree navigation to add the extent map to the tree (if the
   former tree search didn't found anything).

This change just merges these 2 steps into a single one.
While running first few btrfs xfstests I had noticed these trees easily
had a few hundred elements, and then with the following sysbench test it
reached over 1100 elements very often.

Test:

  sysbench --test=fileio --file-num=32 --file-total-size=10G \
    --file-test-mode=seqwr --num-threads=512 --file-block-size=8192 \
    --max-requests=1000000 --file-io-mode=sync [prepare|run]

(fs created with mkfs.btrfs -l 4096 -f /dev/sdb3 before each sysbench
prepare phase)

Before this patch:

run 1 - 41.894Mb/sec
run 2 - 40.527Mb/sec
run 3 - 40.922Mb/sec
run 4 - 49.433Mb/sec
run 5 - 40.959Mb/sec

average - 42.75Mb/sec

After this patch:

run 1 - 48.036Mb/sec
run 2 - 50.21Mb/sec
run 3 - 50.929Mb/sec
run 4 - 46.881Mb/sec
run 5 - 53.192Mb/sec

average - 49.85Mb/sec

Signed-off-by: Filipe David Borba Manana <fdmanana@gmail.com>
Signed-off-by: Josef Bacik <jbacik@fb.com>
Signed-off-by: Chris Mason <clm@fb.com>

diff --git a/fs/btrfs/extent_map.c b/fs/btrfs/extent_map.c
index a4a7a1a8da95c4c1e7571d99e0d58a7b5209f4ee..b60955d4f9bfed5b5c086f85d4a23dfabd52a6fc 100644 (file)
--- a/fs/btrfs/extent_map.c
+++ b/fs/btrfs/extent_map.c
@@ -79,12 +79,21 @@ void free_extent_map(struct extent_map *em)
        }
 }
 
-static struct rb_node *tree_insert(struct rb_root *root, u64 offset,
-                                  struct rb_node *node)
+/* simple helper to do math around the end of an extent, handling wrap */
+static u64 range_end(u64 start, u64 len)
+{
+       if (start + len < start)
+               return (u64)-1;
+       return start + len;
+}
+
+static int tree_insert(struct rb_root *root, struct extent_map *em)
 {
        struct rb_node **p = &root->rb_node;
        struct rb_node *parent = NULL;
-       struct extent_map *entry;
+       struct extent_map *entry = NULL;
+       struct rb_node *orig_parent = NULL;
+       u64 end = range_end(em->start, em->len);
 
        while (*p) {
                parent = *p;
@@ -92,19 +101,37 @@ static struct rb_node *tree_insert(struct rb_root *root, u64 offset,
 
                WARN_ON(!entry->in_tree);
 
-               if (offset < entry->start)
+               if (em->start < entry->start)
                        p = &(*p)->rb_left;
-               else if (offset >= extent_map_end(entry))
+               else if (em->start >= extent_map_end(entry))
                        p = &(*p)->rb_right;
                else
-                       return parent;
+                       return -EEXIST;
        }
 
-       entry = rb_entry(node, struct extent_map, rb_node);
-       entry->in_tree = 1;
-       rb_link_node(node, parent, p);
-       rb_insert_color(node, root);
-       return NULL;
+       orig_parent = parent;
+       while (parent && em->start >= extent_map_end(entry)) {
+               parent = rb_next(parent);
+               entry = rb_entry(parent, struct extent_map, rb_node);
+       }
+       if (parent)
+               if (end > entry->start && em->start < extent_map_end(entry))
+                       return -EEXIST;
+
+       parent = orig_parent;
+       entry = rb_entry(parent, struct extent_map, rb_node);
+       while (parent && em->start < entry->start) {
+               parent = rb_prev(parent);
+               entry = rb_entry(parent, struct extent_map, rb_node);
+       }
+       if (parent)
+               if (end > entry->start && em->start < extent_map_end(entry))
+                       return -EEXIST;
+
+       em->in_tree = 1;
+       rb_link_node(&em->rb_node, orig_parent, p);
+       rb_insert_color(&em->rb_node, root);
+       return 0;
 }
 
 /*
@@ -310,20 +337,11 @@ int add_extent_mapping(struct extent_map_tree *tree,
                       struct extent_map *em, int modified)
 {
        int ret = 0;
-       struct rb_node *rb;
-       struct extent_map *exist;
 
-       exist = lookup_extent_mapping(tree, em->start, em->len);
-       if (exist) {
-               free_extent_map(exist);
-               ret = -EEXIST;
-               goto out;
-       }
-       rb = tree_insert(&tree->map, em->start, &em->rb_node);
-       if (rb) {
-               ret = -EEXIST;
+       ret = tree_insert(&tree->map, em);
+       if (ret)
                goto out;
-       }
+
        atomic_inc(&em->refs);
 
        em->mod_start = em->start;
@@ -337,14 +355,6 @@ out:
        return ret;
 }
 
-/* simple helper to do math around the end of an extent, handling wrap */
-static u64 range_end(u64 start, u64 len)
-{
-       if (start + len < start)
-               return (u64)-1;
-       return start + len;
-}
-
 static struct extent_map *
 __lookup_extent_mapping(struct extent_map_tree *tree,
                        u64 start, u64 len, int strict)