EXT4 Changes Land For Linux 5.9 With Block Allocator Performance Work

Written by Michael Larabel in Linux Storage on 22 August 2020 at 03:58 AM EDT. 11 Comments
With all the Linux 5.9 kernel changes you may have noticed no major EXT4 file-system pull request was submitted during the kernel merge window the prior two weeks. Fortunately, the EXT4 work has now been sent out and Linus Torvalds honored the late changes for this widely-used Linux file-system.

EXT4 changes don't end up being too terribly exciting given the maturity of the file-system and its widespread use for years, but it does continue seeing new optimizations and other improvements, especially in the areas of FSCRYPT encryption and other new knobs.

For this EXT4 pull request now in Linux 5.9 there is block allocator performance improvements when dealing with very large file-systems and especially when the file-system or files are highly fragmented.

Also new is the "prefetch_block_bitmaps" mount option for file-systems that have space for keeping buddy bitmaps cached to speed-up initial writes to large file-systems. The actual commit does note though that prefetch_block_bitmaps doesn't work well for "super" large file-systems nor memory constrained systems, hence why it's not being enabled by default. This prefetch_block_bitmaps mount option stems from an internal Google issue/bug.

The rest of the EXT4 file-system updates for Linux 5.9 amount to the usual assortment of bug fixes and code clean-ups. More details in the Git merge.
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