Re: [PATCH v2 0/5] mm/shmem: optimize read with reduced xarray lookups and folio batching

[Andrew Morton]

On Mon,  1 Jun 2026 13:56:59 +0800 Chi Zhiling <chizhiling@xxxxxxx> wrote:

> From: Chi Zhiling <chizhiling@xxxxxxxxxx>
> 
> This series improves shmem read performance by implementing folio
> batching in the read path and reducing unnecessary xarray lookups.
> 
> Performance Results:
> 
> fio --ioengine=sync --rw=read --bs=$1 --size=1G --runtime=180 --time_based --group_reporting --name=seq_read_test --filename=testfile
> 
> | THP disabled in tmpfs  | v7.1-rc5     | v7.1-rc5 + fbatch | Improvement |
> | ---------------------- | ------------ | ----------------- | ----------- |
> | 1M + normal file       | bw=11.5GiB/s | bw=12.7GiB/s      | +10.4%      |
> | 64k + normal file      | bw=11.0GiB/s | bw=12.3GiB/s      | +11.8%      |
> | 4k + normal file       | bw=3826MiB/s | bw=3849MiB/s      | +0.6%       |
> | 1M + fallocated file   | bw=23.8GiB/s | bw=28.6GiB/s      | +20.2%      |
> | 64k + fallocated file  | bw=22.5GiB/s | bw=27.3GiB/s      | +21.3%      |
> | 4k + fallocated file   | bw=4655MiB/s | bw=4680MiB/s      | +0.5%       |
> | 1M + hole              | bw=24.2GiB/s | bw=28.6GiB/s      | +18.2%      |
> | 64k + hole             | bw=22.6GiB/s | bw=27.6GiB/s      | +22.1%      |
> | 4k + hole              | bw=4652MiB/s | bw=4489MiB/s      | -3.5%       |
> 
> 
> | THP enabled in tmpfs  | v7.1-rc5     | v7.1-rc5 + fbatch | Improvement |
> | --------------------- | ------------ | ----------------- | ----------- |
> | 1M + normal file      | bw=13.7GiB/s | bw=13.9GiB/s      | +1.4%       |
> | 64k + normal file     | bw=13.5GiB/s | bw=13.5GiB/s      | +0.0%       |
> | 4k + normal file      | bw=3833MiB/s | bw=3859MiB/s      | +0.7%       |
> | 1M + fallocated file  | bw=24.9GiB/s | bw=34.2GiB/s      | +37.3%      |
> | 64k + fallocated file | bw=23.0GiB/s | bw=31.4GiB/s      | +36.5%      |
> | 4k + fallocated file  | bw=4710MiB/s | bw=4655MiB/s      | -1.2%       |
> | 1M + hole             | bw=24.3GiB/s | bw=34.5GiB/s      | +42.0%      |
> | 64k + hole            | bw=23.5GiB/s | bw=31.1GiB/s      | +32.3%      |
> | 4k + hole             | bw=4690MiB/s | bw=4647MiB/s      | -0.9%       |
> 

That looks nice.

Microbenchmarks are useful, but are you able to help us understand how
much benefit our users might see in real-world workloads?

I'll take no action at this time - it's late in the cycle and reviewers
have yet to participate.

AI review flagged a few possible issues, so please take a look:
	https://sashiko.dev/#/patchset/20260601055704.167436-1-chizhiling@xxxxxxx