Re: [PATCH] ext4: rralloc - (former rotalloc) improved round-robin allocation policy

[Mario Lohajner]

On 27. 02. 2026. 17:43, Theodore Tso wrote:
> On Fri, Feb 27, 2026 at 03:46:59PM +0100, Mario Lohajner wrote:
> > Concentrated allocation can create contention, write amplification, and
> > uneven LBA utilization even on modern NVMe/SSD devices.
>
> Uneven LBA utilization is the thing where I'm asking, "why should we care".
>
> In terms of how this would cause contention and write amplification,
> <<citation needed>>.  What is your benchmarks where you can
> demonstrate this, and how common is this across NVMe/SSD devices?
> That is, if it's just one trashy product, maybe it should just be
> avoided --- especially if it has other problems.
>
> 						- Ted

RRALLOC spreads allocation starting points across block groups to avoid
repeated concentration under parallel load.

This reduces short-term allocation concentration in the same regions
when multiple CPUs allocate concurrently.

In high-concurrency testing, performance is consistently comparable to
or occasionally better than the regular allocator. No regressions have
been observed across tested configurations.

Under sustained parallel allocation pressure, testing shows improved
tail-latency stability compared to the current allocator.

Additional high-concurrency test results are available at:
https://github.com/mlohajner/RRALLOC

Regards,
Mario Lohajner