Benchmarks Of The Btrfs Space Cache Option
When beginning with the SQLite database benchmark, there was a small improvement in performance when enabling space_cache, but the impact of enabling the Zlib disk compression was much greater. When both the Btrfs compression and space caching were enabled, there really was not any measurable benefit over using compress without space_cache.
The Apache benchmark really was not impacted much on the Linux 2.6.37 kernel by the compress or space_cache mount options, but when both compress and space_cache were used, there was a very strange performance drop that completely slaughtered the web server's abilities.
With the Compile Bench test profile there was a small boost in performance when enabling space_cache, but again the compress mount option provided a much more dramatic improvement.