Re: [PATCH] io_uring: support async buffered reads when readahead is disabled

[Jens Axboe <axboe@kernel.dk>]

On 9/29/20 6:00 AM, Hao Xu wrote:
> The async buffered reads feature is not working when readahead is
> turned off. There are two things to concern:
> 
> - when doing retry in io_read, not only the IOCB_WAITQ flag but also
>   the IOCB_NOWAIT flag is still set, which makes it goes to would_block
>   phase in generic_file_buffered_read() and then return -EAGAIN. After
>   that, the io-wq thread work is queued, and later doing the async
>   reads in the old way.
> 
> - even if we remove IOCB_NOWAIT when doing retry, the feature is still
>   not running properly, since in generic_file_buffered_read() it goes to
>   lock_page_killable() after calling mapping->a_ops->readpage() to do
>   IO, and thus causing process to sleep.

Thanks, this looks great, and avoids cases of io-wq punt where we don't
need it. I'm going to run this through full testing, but I think this
looks good to me.

-- 
Jens Axboe