Re: [PATCH v2 1/1] iomap: propagate nowait to block layer

[Pavel Begunkov <asml.silence@gmail.com>]

On 3/5/25 00:01, Christoph Hellwig wrote:
> On Tue, Mar 04, 2025 at 08:35:52PM +0000, Pavel Begunkov wrote:
>> Clarification: the mentioned work was reverted or pulled out _upstream_,
>> it wasn't about back porting.
> 
> I don't think we ever tried synchronous reporting of wouldblock errors,
> but maybe i'm just too old and confused by now.

It's not something recent. After some digging I think the
one I remember is

https://lore.kernel.org/all/20190717150445.1131-2-axboe@kernel.dk/

Remove by

commit 7b6620d7db566a46f49b4b9deab9fa061fd4b59b
Author: Jens Axboe <axboe@kernel.dk>
Date:   Thu Aug 15 11:09:16 2019 -0600

     block: remove REQ_NOWAIT_INLINE


>> lines. And Christoph even of confirmed that the main check in the patch
>> does what's intended,
> 
> I absolutely did not.
> 
>> Another option is to push all io_uring filesystem / iomap requests
>> to the slow path (where blocking is possible) and have a meaningful
>> perf regression for those who still use fs+io_uring direct IO. And
>> I don't put any dramaticism into it, it's essentially what users
>> who detect the problem already do, either that but from the user
>> space or disabling io_uring all together.
> 
> If you don't want to do synchronous wouldblock errors that's your
> only option.  I think it would suck badly, but it's certainly easier
> to backport.

Is there some intrinsic difference of iomap from the block file
in block/fops.c? Or is that one broken?

-- 
Pavel Begunkov