btrfs: use a regular rb_root instead of cached rb_root for extent_map_tree

We are currently using a cached rb_root (struct rb_root_cached) for the
rb root of struct extent_map_tree. This doesn't offer much of an advantage
here because:

1) It's only advantage over the regular rb_root is that it caches a
   pointer to the left most node (first node), so a call to
   rb_first_cached() doesn't have to chase pointers until it reaches
   the left most node;

2) We only have two scenarios that access left most node with
   rb_first_cached():

      When dropping all extent maps from an inode, during inode eviction;

      When iterating over extent maps during the extent map shrinker;

3) In both cases we keep removing extent maps, which causes deletion of
   the left most node so rb_erase_cached() has to call rb_next() to find
   out what's the next left most node and assign it to
   struct rb_root_cached::rb_leftmost;

4) We can do that ourselves in those two uses cases and stop using a
   rb_root_cached rb tree and use instead a regular rb_root rb tree.

   This reduces the size of struct extent_map_tree by 8 bytes and, since
   this structure is embedded in struct btrfs_inode, it also reduces the
   size of that structure by 8 bytes.

   So on a 64 bits platform the size of btrfs_inode is reduced from 1032
   bytes down to 1024 bytes.

   This means we will be able to have 4 inodes per 4K page instead of 3.

Signed-off-by: Filipe Manana <fdmanana@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

diff --git a/fs/btrfs/extent_map.c b/fs/btrfs/extent_map.c
index 4bc41b0dd7019a0088cf9b6448a2e3f3517118f8..35e163152dbc0f44b3dcf032639d0a4bc50f2f2c 100644 (file)
--- a/fs/btrfs/extent_map.c
+++ b/fs/btrfs/extent_map.c
@@ -33,7 +33,7 @@ void __cold extent_map_exit(void)
  */
 void extent_map_tree_init(struct extent_map_tree *tree)
 {
-       tree->root = RB_ROOT_CACHED;
+       tree->root = RB_ROOT;
        INIT_LIST_HEAD(&tree->modified_extents);
        rwlock_init(&tree->lock);
 }
@@ -85,27 +85,24 @@ static void dec_evictable_extent_maps(struct btrfs_inode *inode)
                percpu_counter_dec(&fs_info->evictable_extent_maps);
 }
 
-static int tree_insert(struct rb_root_cached *root, struct extent_map *em)
+static int tree_insert(struct rb_root *root, struct extent_map *em)
 {
-       struct rb_node **p = &root->rb_root.rb_node;
+       struct rb_node **p = &root->rb_node;
        struct rb_node *parent = NULL;
        struct extent_map *entry = NULL;
        struct rb_node *orig_parent = NULL;
        u64 end = range_end(em->start, em->len);
-       bool leftmost = true;
 
        while (*p) {
                parent = *p;
                entry = rb_entry(parent, struct extent_map, rb_node);
 
-               if (em->start < entry->start) {
+               if (em->start < entry->start)
                        p = &(*p)->rb_left;
-               } else if (em->start >= extent_map_end(entry)) {
+               else if (em->start >= extent_map_end(entry))
                        p = &(*p)->rb_right;
-                       leftmost = false;
-               } else {
+               else
                        return -EEXIST;
-               }
        }
 
        orig_parent = parent;
@@ -128,7 +125,7 @@ static int tree_insert(struct rb_root_cached *root, struct extent_map *em)
                        return -EEXIST;
 
        rb_link_node(&em->rb_node, orig_parent, p);
-       rb_insert_color_cached(&em->rb_node, root, leftmost);
+       rb_insert_color(&em->rb_node, root);
        return 0;
 }
 
@@ -265,7 +262,7 @@ static void try_merge_map(struct btrfs_inode *inode, struct extent_map *em)
                        em->generation = max(em->generation, merge->generation);
                        em->flags |= EXTENT_FLAG_MERGED;
 
-                       rb_erase_cached(&merge->rb_node, &tree->root);
+                       rb_erase(&merge->rb_node, &tree->root);
                        RB_CLEAR_NODE(&merge->rb_node);
                        free_extent_map(merge);
                        dec_evictable_extent_maps(inode);
@@ -278,7 +275,7 @@ static void try_merge_map(struct btrfs_inode *inode, struct extent_map *em)
        if (rb && can_merge_extent_map(merge) && mergeable_maps(em, merge)) {
                em->len += merge->len;
                em->block_len += merge->block_len;
-               rb_erase_cached(&merge->rb_node, &tree->root);
+               rb_erase(&merge->rb_node, &tree->root);
                RB_CLEAR_NODE(&merge->rb_node);
                em->generation = max(em->generation, merge->generation);
                em->flags |= EXTENT_FLAG_MERGED;
@@ -410,7 +407,7 @@ __lookup_extent_mapping(struct extent_map_tree *tree,
        struct rb_node *prev_or_next = NULL;
        u64 end = range_end(start, len);
 
-       rb_node = __tree_search(&tree->root.rb_root, start, &prev_or_next);
+       rb_node = __tree_search(&tree->root, start, &prev_or_next);
        if (!rb_node) {
                if (prev_or_next)
                        rb_node = prev_or_next;
@@ -479,7 +476,7 @@ void remove_extent_mapping(struct btrfs_inode *inode, struct extent_map *em)
        lockdep_assert_held_write(&tree->lock);
 
        WARN_ON(em->flags & EXTENT_FLAG_PINNED);
-       rb_erase_cached(&em->rb_node, &tree->root);
+       rb_erase(&em->rb_node, &tree->root);
        if (!(em->flags & EXTENT_FLAG_LOGGING))
                list_del_init(&em->list);
        RB_CLEAR_NODE(&em->rb_node);
@@ -500,7 +497,7 @@ static void replace_extent_mapping(struct btrfs_inode *inode,
        ASSERT(extent_map_in_tree(cur));
        if (!(cur->flags & EXTENT_FLAG_LOGGING))
                list_del_init(&cur->list);
-       rb_replace_node_cached(&cur->rb_node, &new->rb_node, &tree->root);
+       rb_replace_node(&cur->rb_node, &new->rb_node, &tree->root);
        RB_CLEAR_NODE(&cur->rb_node);
 
        setup_extent_mapping(inode, new, modified);
@@ -657,18 +654,23 @@ int btrfs_add_extent_mapping(struct btrfs_inode *inode,
 static void drop_all_extent_maps_fast(struct btrfs_inode *inode)
 {
        struct extent_map_tree *tree = &inode->extent_tree;
+       struct rb_node *node;
 
        write_lock(&tree->lock);
-       while (!RB_EMPTY_ROOT(&tree->root.rb_root)) {
+       node = rb_first(&tree->root);
+       while (node) {
                struct extent_map *em;
-               struct rb_node *node;
+               struct rb_node *next = rb_next(node);
 
-               node = rb_first_cached(&tree->root);
                em = rb_entry(node, struct extent_map, rb_node);
                em->flags &= ~(EXTENT_FLAG_PINNED | EXTENT_FLAG_LOGGING);
                remove_extent_mapping(inode, em);
                free_extent_map(em);
-               cond_resched_rwlock_write(&tree->lock);
+
+               if (cond_resched_rwlock_write(&tree->lock))
+                       node = rb_first(&tree->root);
+               else
+                       node = next;
        }
        write_unlock(&tree->lock);
 }
@@ -1058,12 +1060,12 @@ static long btrfs_scan_inode(struct btrfs_inode *inode, long *scanned, long nr_t
                return 0;
 
        write_lock(&tree->lock);
-       node = rb_first_cached(&tree->root);
+       node = rb_first(&tree->root);
        while (node) {
+               struct rb_node *next = rb_next(node);
                struct extent_map *em;
 
                em = rb_entry(node, struct extent_map, rb_node);
-               node = rb_next(node);
                (*scanned)++;
 
                if (em->flags & EXTENT_FLAG_PINNED)
@@ -1094,7 +1096,9 @@ next:
                 * lock and took it again.
                 */
                if (cond_resched_rwlock_write(&tree->lock))
-                       node = rb_first_cached(&tree->root);
+                       node = rb_first(&tree->root);
+               else
+                       node = next;
        }
        write_unlock(&tree->lock);
        up_read(&inode->i_mmap_lock);

diff --git a/fs/btrfs/extent_map.h b/fs/btrfs/extent_map.h
index 9c0793888d1347fa9caa460b68625fef6d5766a8..9144721b88a55e7328cb62a6b61d1c6f40a368b3 100644 (file)
--- a/fs/btrfs/extent_map.h
+++ b/fs/btrfs/extent_map.h
@@ -115,7 +115,7 @@ struct extent_map {
 };
 
 struct extent_map_tree {
-       struct rb_root_cached root;
+       struct rb_root root;
        struct list_head modified_extents;
        rwlock_t lock;
 };

diff --git a/fs/btrfs/tests/extent-map-tests.c b/fs/btrfs/tests/extent-map-tests.c
index 075e6930acda56bc677254b5d67860580597aa77..c511a1297956fa80c1936a96896bcccdbf2670aa 100644 (file)
--- a/fs/btrfs/tests/extent-map-tests.c
+++ b/fs/btrfs/tests/extent-map-tests.c
@@ -19,8 +19,8 @@ static int free_extent_map_tree(struct btrfs_inode *inode)
        int ret = 0;
 
        write_lock(&em_tree->lock);
-       while (!RB_EMPTY_ROOT(&em_tree->root.rb_root)) {
-               node = rb_first_cached(&em_tree->root);
+       while (!RB_EMPTY_ROOT(&em_tree->root)) {
+               node = rb_first(&em_tree->root);
                em = rb_entry(node, struct extent_map, rb_node);
                remove_extent_mapping(inode, em);
 
@@ -551,7 +551,7 @@ static int validate_range(struct extent_map_tree *em_tree, int index)
        struct rb_node *n;
        int i;
 
-       for (i = 0, n = rb_first_cached(&em_tree->root);
+       for (i = 0, n = rb_first(&em_tree->root);
             valid_ranges[index][i].len && n;
             i++, n = rb_next(n)) {
                struct extent_map *entry = rb_entry(n, struct extent_map, rb_node);