Re: [PATCH] mm: mark async iocb read as NOWAIT once some data has been, copied

[Jens Axboe <axboe@kernel.dk>]

On 10/17/20 10:28 AM, Matthew Wilcox wrote:
> On Sat, Oct 17, 2020 at 09:30:59AM -0600, Jens Axboe wrote:
>> Once we've copied some data for an iocb that is marked with IOCB_WAITQ,
>> we should no longer attempt to async lock a new page. Instead make sure
>> we return the copied amount, and let the caller retry, instead of
>> returning -EIOCBQUEUED for a new page.
>>
>> This should only be possible with read-ahead disabled on the below
>> device, and multiple threads racing on the same file. Haven't been able
>> to reproduce on anything else.
> 
> Wouldn't this do the job just as well?
> 
> @@ -2211,6 +2211,8 @@ ssize_t generic_file_buffered_read(struct kiocb *iocb,
>  
>                 put_page(page);
>                 written += ret;
> +               if (iocb->ki_flags & IOCB_WAITQ)
> +                       iocb->ki_flags |= IOCB_NOWAIT;
>                 if (!iov_iter_count(iter))
>                         goto out;
>                 if (ret < nr) {

Indeed, that's cleaner. Let me re-test with that just to be on the safe
side, and I'll post a new one.

-- 
Jens Axboe