btrfs: search for last logged dir index if it's not cached in the inode

The key offset of the last dir index item that was logged is stored in
the inode's last_dir_index_offset field. However that field is not
persisted in the inode item or elsewhere, so if the inode gets evicted
and reloaded, it gets a value of (u64)-1, so that when we are logging
dir index items we check if they were logged before, to avoid attempts
to insert duplicated keys and fallback to a transaction commit.

Improve on this by searching for the last dir index that was logged when
we start logging a directory if the inode's last_dir_index_offset is not
set (has a value of (u64)-1) and it was logged before. This avoids
checking if each dir index item we find was already logged before, and
simplifies the logging of dir index items (process_dir_items_leaf()).

This will also be needed for an incoming change where we start logging
delayed items directly, without flushing them first.

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

Author: fdmanana

fs/btrfs/tree-log.c

@@ -3875,6 +3875,11 @@ static int process_dir_items_leaf(struct btrfs_trans_handle *trans,
 			*last_old_dentry_offset = key.offset;
 			continue;
 		}
+
+		/* If we logged this dir index item before, we can skip it. */
+		if (key.offset <= inode->last_dir_index_offset)
+			continue;
+
 		/*
 		 * We must make sure that when we log a directory entry, the
 		 * corresponding inode, after log replay, has a matching link
@@ -3905,51 +3910,6 @@ static int process_dir_items_leaf(struct btrfs_trans_handle *trans,
 				ctx->log_new_dentries = true;
 		}
 
-		if (!ctx->logged_before)
-			goto add_to_batch;
-
-		/*
-		 * If we were logged before and have logged dir items, we can skip
-		 * checking if any item with a key offset larger than the last one
-		 * we logged is in the log tree, saving time and avoiding adding
-		 * contention on the log tree. We can only rely on the value of
-		 * last_dir_index_offset when we know for sure that the inode was
-		 * previously logged in the current transaction.
-		 */
-		if (key.offset > inode->last_dir_index_offset)
-			goto add_to_batch;
-		/*
-		 * Check if the key was already logged before. If not we can add
-		 * it to a batch for bulk insertion.
-		 */
-		ret = btrfs_search_slot(NULL, log, &key, dst_path, 0, 0);
-		if (ret < 0) {
-			return ret;
-		} else if (ret > 0) {
-			btrfs_release_path(dst_path);
-			goto add_to_batch;
-		}
-
-		/*
-		 * Item exists in the log. Overwrite the item in the log if it
-		 * has different content or do nothing if it has exactly the same
-		 * content. And then flush the current batch if any - do it after
-		 * overwriting the current item, or we would deadlock otherwise,
-		 * since we are holding a path for the existing item.
-		 */
-		ret = do_overwrite_item(trans, log, dst_path, src, i, &key);
-		if (ret < 0)
-			return ret;
-
-		if (batch_size > 0) {
-			ret = flush_dir_items_batch(trans, log, src, dst_path,
-						    batch_start, batch_size);
-			if (ret < 0)
-				return ret;
-			batch_size = 0;
-		}
-		continue;
-add_to_batch:
 		if (batch_size == 0)
 			batch_start = i;
 		batch_size++;
@@ -4135,6 +4095,71 @@ static noinline int log_dir_items(struct btrfs_trans_handle *trans,
 	return err;
 }
 
+/*
+ * If the inode was logged before and it was evicted, then its
+ * last_dir_index_offset is (u64)-1, so we don't the value of the last index
+ * key offset. If that's the case, search for it and update the inode. This
+ * is to avoid lookups in the log tree every time we try to insert a dir index
+ * key from a leaf changed in the current transaction, and to allow us to always
+ * do batch insertions of dir index keys.
+ */
+static int update_last_dir_index_offset(struct btrfs_inode *inode,
+					struct btrfs_path *path,
+					const struct btrfs_log_ctx *ctx)
+{
+	const u64 ino = btrfs_ino(inode);
+	struct btrfs_key key;
+	int ret;
+
+	lockdep_assert_held(&inode->log_mutex);
+
+	if (inode->last_dir_index_offset != (u64)-1)
+		return 0;
+
+	if (!ctx->logged_before) {
+		inode->last_dir_index_offset = BTRFS_DIR_START_INDEX - 1;
+		return 0;
+	}
+
+	key.objectid = ino;
+	key.type = BTRFS_DIR_INDEX_KEY;
+	key.offset = (u64)-1;
+
+	ret = btrfs_search_slot(NULL, inode->root->log_root, &key, path, 0, 0);
+	/*
+	 * An error happened or we actually have an index key with an offset
+	 * value of (u64)-1. Bail out, we're done.
+	 */
+	if (ret <= 0)
+		goto out;
+
+	ret = 0;
+	inode->last_dir_index_offset = BTRFS_DIR_START_INDEX - 1;
+
+	/*
+	 * No dir index items, bail out and leave last_dir_index_offset with
+	 * the value right before the first valid index value.
+	 */
+	if (path->slots[0] == 0)
+		goto out;
+
+	/*
+	 * btrfs_search_slot() left us at one slot beyond the slot with the last
+	 * index key, or beyond the last key of the directory that is not an
+	 * index key. If we have an index key before, set last_dir_index_offset
+	 * to its offset value, otherwise leave it with a value right before the
+	 * first valid index value, as it means we have an empty directory.
+	 */
+	btrfs_item_key_to_cpu(path->nodes[0], &key, path->slots[0] - 1);
+	if (key.objectid == ino && key.type == BTRFS_DIR_INDEX_KEY)
+		inode->last_dir_index_offset = key.offset;
+
+out:
+	btrfs_release_path(path);
+
+	return ret;
+}
+
 /*
  * logging directories is very similar to logging inodes, We find all the items
  * from the current transaction and write them to the log.
@@ -4157,6 +4182,10 @@ static noinline int log_directory_changes(struct btrfs_trans_handle *trans,
 	u64 max_key;
 	int ret;
 
+	ret = update_last_dir_index_offset(inode, path, ctx);
+	if (ret)
+		return ret;
+
 	min_key = BTRFS_DIR_START_INDEX;
 	max_key = 0;
 	ctx->last_dir_item_offset = inode->last_dir_index_offset;