Btrfs: switch extent_map to a rw lock

There are two main users of the extent_map tree.  The
first is regular file inodes, where it is evenly spread
between readers and writers.

The second is the chunk allocation tree, which maps blocks from
logical addresses to phyiscal ones, and it is 99.99% reads.

The mapping tree is a point of lock contention during heavy IO
workloads, so this commit switches things to a rw lock.

Signed-off-by: Chris Mason <chris.mason@oracle.com>

1 files changed, 1 insertions, 4 deletions

diff --git a/fs/btrfs/extent_map.c b/fs/btrfs/extent_map.c
index 30c9365861e6..72e9fa3c31f5 100644
--- a/fs/btrfs/extent_map.c
+++ b/fs/btrfs/extent_map.c
@@ -36,7 +36,7 @@ void extent_map_exit(void)
 void extent_map_tree_init(struct extent_map_tree *tree, gfp_t mask)
 {
         tree->map.rb_node = NULL;
-        spin_lock_init(&tree->lock);
+        rwlock_init(&tree->lock);
 }
 
 /**
@@ -222,7 +222,6 @@ int add_extent_mapping(struct extent_map_tree *tree,
                 ret = -EEXIST;
                 goto out;
         }
-        assert_spin_locked(&tree->lock);
         rb = tree_insert(&tree->map, em->start, &em->rb_node);
         if (rb) {
                 ret = -EEXIST;
@@ -285,7 +284,6 @@ struct extent_map *lookup_extent_mapping(struct extent_map_tree *tree,
         struct rb_node *next = NULL;
         u64 end = range_end(start, len);
 
-        assert_spin_locked(&tree->lock);
         rb_node = __tree_search(&tree->map, start, &prev, &next);
         if (!rb_node && prev) {
                 em = rb_entry(prev, struct extent_map, rb_node);
@@ -331,7 +329,6 @@ int remove_extent_mapping(struct extent_map_tree *tree, struct extent_map *em)
         int ret = 0;
 
         WARN_ON(test_bit(EXTENT_FLAG_PINNED, &em->flags));
-        assert_spin_locked(&tree->lock);
         rb_erase(&em->rb_node, &tree->map);
         em->in_tree = 0;
         return ret;