EXT4 Ready With Some New Optimizations - Orphan_File, Moving Discard's Work
Written by Michael Larabel in Linux Storage on 2 September 2021 at 01:44 PM EDT. 2 Comments
LINUX STORAGE --
It's busy on the Linux file-system front for the 5.15 cycle with Btrfs adding a degenerate RAID option along with performance improvements to big improvements for XFS and now comes the EXT4 updates.

With EXT4 there are various fixes and improvements as usual but this cycle does bring some new performance work too.

First up, EXT4 adds a new "orphan_file" mount option to speed-up its handling of orphan file handling. As summed up by Jan Kara with the orphan file improvement patch series, "Orphan inode handling in ext4 is a bottleneck for workloads which heavily excercise truncate / unlink of small files as they contend on global s_orphan_mutex (when you have fast enough storage). This patch set implements new way of handling orphan inodes - instead of using a linked list, we store inode numbers of orphaned inodes in a file which is possible to implement in a more scalable manner than linked list manipulations."

This new orphan_file feature should eliminate bottlenecks in such cases of large parallel truncates and file deletions. With a micro-benchmark truncating files byte-by-byte in parallel, with many threads it could mean dropping from a 206 second run-time down to 122 seconds in the peak scenario tested. But even in a single thread scenario it meant a drop from 1.057 seconds to 0.945 seconds and the wins scaled up with the level of parallelism.

Another significant optimization with Linux 5.15 for EXT4 is moving the DISCARD work out of the JBD2 commit thread when having the "discard" mount option enabled. This should help out with devices having slow DISCARD behavior and not blocking the JBD2 commit KThread.

More details on all of the EXT4 improvements for Linux 5.15 via this pull request.
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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 20,000 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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