btrfs: pass a pointer to get_range_bits() to cache first search result

Allow get_range_bits() to take an extent state pointer to pointer argument
so that we can cache the first extent state record in the target range, so
that a caller can use it for subsequent operations without doing a full
tree search. Currently the only user is try_release_extent_state(), which
then does a call to __clear_extent_bit() which can use such a cached state
record.

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

1 files changed, 13 insertions, 1 deletions

diff --git a/fs/btrfs/extent-io-tree.c b/fs/btrfs/extent-io-tree.c
index 14510a71a8fd..7ae24a533404 100644
--- a/fs/btrfs/extent-io-tree.c
+++ b/fs/btrfs/extent-io-tree.c
@@ -1752,14 +1752,26 @@ bool test_range_bit_exists(struct extent_io_tree *tree, u64 start, u64 end, u32
 	return bitset;
 }
 
-void get_range_bits(struct extent_io_tree *tree, u64 start, u64 end, u32 *bits)
+void get_range_bits(struct extent_io_tree *tree, u64 start, u64 end, u32 *bits,
+		    struct extent_state **cached_state)
 {
 	struct extent_state *state;
 
+	/*
+	 * The cached state is currently mandatory and not used to start the
+	 * search, only to cache the first state record found in the range.
+	 */
+	ASSERT(cached_state != NULL);
+	ASSERT(*cached_state == NULL);
+
 	*bits = 0;
 
 	spin_lock(&tree->lock);
 	state = tree_search(tree, start);
+	if (state && state->start < end) {
+		*cached_state = state;
+		refcount_inc(&state->refs);
+	}
 	while (state) {
 		if (state->start > end)
 			break;