1. A system comprising: a central processing unit (CPU) adapted to execute a storage input/output (I/O) stack; one or more solid state drives (SSDs) coupled to the CPU; and a memory coupled to the CPU and configured to store the storage I/O stack and a multi-level dense tree metadata structure, wherein each level of the dense tree metadata structure includes entries for storing metadata having mappings from offset ranges of a logical unit (LUN) to extent keys associated with storage locations for extents stored on an extent store of the SSDs, wherein the storage I/O stack is configured to: receive overlapping write requests directed to the LUN, the overlapping write requests representing overlapping offset ranges of the LUN, the overlapping offset ranges stored as overlapping entries of the dense tree metadata structure; process the mappings of the overlapping entries to determine an offset range overlap of the overlapping entries per level; and aggregate the offset range overlap of the overlapping entries between adjacent levels of the multi-level dense tree metadata structure to quantify trapped logical storage space in overlapping extents of the extent store due to the overlapping write requests.