Btrfs In Linux 4.1 Has Fixes For File-Systems Of 20 Terabytes & Up
This pull request is coming in late in part due to him running a longer series of load tests than normal. For this cycle he changed around the free space cache writeout and wanted to ensure the code is properly conditioned. Changing the free space cache writeout should fix stalls on large file-systems. In particular, over at Facebook they were seeing 10+ second stalls during commits on file-systems with around twenty terabytes of space and greater. Should you happen to have a 20TB+ Btrfs file-system, Linux 4.1 will perform better.
There's also fixes in Btrfs for Linux 4.1 when deleting "huge files" of three terabytes or more.
More details on the Btrfs changes for Linux 4.1 can be found in this pull request by Facebook's Chris Mason.