Facebook Has Been Baking A New Space Cache System For Btrfs
Written by Michael Larabel in Linux Storage on 17 January 2016 at 06:56 PM EST. 5 Comments
LINUX STORAGE --
The Btrfs file-system updates were mailed in Sunday evening for the Linux 4.5 kernel. There is one big but experimental feature with this pull.

Btrfs for Linux 4.5 includes fixes and clean-ups with over 70 commits being sent in for landing during the Linux 4.5 merge window. The big feature for Linux 4.5 is a new free space tree, but it's not yet enabled by default -- though testing it out is easy via the space_cache=v2 mount option. While experimental, it is possible to re-generate the tree in case of problems.

Btrfs lead developer Chris Mason explained that this forthcoming free space cache is tree-based and is faster with less overall work for updating as the commit progresses.

Development on this free space tree was led by Omar Sandoval, a computer engineering student that was interning at Facebook over the summer. This space cache is being redone as Facebook found that for large file-systems the free space caching code was taking a long time during commits. Fortunately, most users won't see these current limitations as the slowdowns were reported for file-systems of around 30+ Terabytes.
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Michael Larabel is the principal author of Phoronix.com and founded the site in 2004 with a focus on enriching the Linux hardware experience. Michael has written more than 10,000 articles covering the state of Linux hardware support, Linux performance, graphics drivers, and other topics. Michael is also the lead developer of the Phoronix Test Suite, Phoromatic, and OpenBenchmarking.org automated benchmarking software. He can be followed via Twitter or contacted via MichaelLarabel.com.

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