On 9/8/21 11:25 AM, Greg Kroah-Hartman wrote:

On Wed, Sep 08, 2021 at 11:06:51AM +0100, Pavel Begunkov wrote:

quoted

Make read_iter_zero() to honor IOCB_NOWAIT, so /dev/zero can be
advertised as FMODE_NOWAIT. This helps subsystems like io_uring to use
it more effectively. Set FMODE_NOWAIT for /dev/null as well, it never
waits and therefore trivially meets the criteria.

I do not understand, why would io_uring need to use /dev/zero

Not directly, users can issue I/O against it via io_uring.
 

and how is this going to help anything?

For files not supporting nowait io_uring goes through a quite slow path.

What workload does this help with?

Personally for me it's dumping output and benchmarking (not benchmarking
/dev/zero, of course). But I'd also expect any tool that may be using
it but rewritten with io_uring being able to normally use it without a
performance hit.

-- 
Pavel Begunkov