
Queued within the EXT4 development code ahead of Linux 5.6 is optimize EXT4 DIO overwrites by SUSE's Jan Kara. This optimization about Direct I/O when overwriting already allocated blocks is particularly beneficial for multi-threaded workloads engaging in small writes.
When testing with FIO for performing 4K random writes, Kara found that the performance went up from 3018MB/s to 4059MB/s or when using direct access (DAX) the improvement went from 3042MB/s to 4311MB/s. This optimization just affects the performance when writing over already allocated blocks and won't have any performance improvements for reads or other non-DIO areas.
Quite the win for EXT4 Direct I/O performance come Linux 5.6!
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