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From: Jens Axboe <axboe@kernel.dk>
To: Hao Xu <haoxu@linux.alibaba.com>, io-uring@vger.kernel.org
Cc: viro@zeniv.linux.org.uk, akpm@linux-foundation.org,
	hannes@cmpxchg.org, linux-fsdevel@vger.kernel.org,
	linux-mm@kvack.org
Subject: Re: [PATCH] io_uring: support async buffered reads when readahead is disabled
Date: Tue, 29 Sep 2020 07:51:55 -0600	[thread overview]
Message-ID: <6ef7da28-f6a6-827e-4881-dd78a4b92bf5@kernel.dk> (raw)
In-Reply-To: <1601380845-206925-1-git-send-email-haoxu@linux.alibaba.com>

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


      reply	other threads:[~2020-09-29 13:51 UTC|newest]

Thread overview: 2+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-09-29 12:00 [PATCH] io_uring: support async buffered reads when readahead is disabled Hao Xu
2020-09-29 13:51 ` Jens Axboe [this message]

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