Re: bounce buffer direct I/O when stable pages are required v2

[Keith Busch <kbusch@kernel.org>]

On Fri, Jan 23, 2026 at 05:40:26PM +0530, Anuj Gupta wrote:
> Sequential read
>   | size | zero copy  |  bounce    |   +------+------------+------------+
>   |   4k | 1693MiB/s  | 1245MiB/s  |
>   |  64K | 6518MiB/s  | 4763MiB/s  |
>   |   1M | 6731MiB/s  | 5475MiB/s  |
>   +------+-------------------------+
> For Samsung PM1733:
> 
> Sequential write
>   | size | zero copy  |  bounce    |   +------+------------+------------+
>   |   4k | 155MiB/s   | 153MiB/s   |
>   |  64K | 3899MiB/s  | 3868MiB/s  |
>   |   1M | 4117MiB/s  | 4116MiB/s  |
>   +------+-------------------------+
> 
> Sequential read
>   | size | zero copy  |  bounce    |   +------+------------+------------+
>   |   4k | 602MiB/s   | 244MiB/s  |
>   |  64K | 4613MiB/s  | 2141MiB/s  |
>   |   1M | 5868MiB/s  | 5162MiB/s  |
>   +------+-------------------------+
> 
> [2]
> Write benchmark -
> fio --name=write_new_4k --filename=/mnt/writefile --rw=write --bs=4k --size=20G --ioengine=io_uring --direct=1 --iodepth=16 --numjobs=1 --time_based=1 --runtime=30 --group_reporting
> 
> Read benchmark -
> Prepare the file:
> fio --name=prep_create_prepfile --filename=/mnt/prepfile --rw=write --bs=1M --size=20G --ioengine=io_uring --direct=1 --iodepth=16 --numjobs=1 --group_reporting
> 
> Then run the read workload:
> fio --name=read_4k --filename=/mnt/prepfile --rw=read --bs=4k --size=20G --ioengine=io_uring --direct=1 --iodepth=16 --numjobs=1 --time_based=1 --runtime=30 --group_reporting

For this change, I think it'd be more meaningful to report latency
rather than throughput. Can you try a QD1 workload instead?