From: Pavel Begunkov <asml.silence@gmail.com>
To: Jens Axboe <axboe@kernel.dk>, io-uring@vger.kernel.org
Cc: linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org,
linux-mm@kvack.org
Subject: Re: [PATCH 12/12] io_uring: support true async buffered reads, if file provides it
Date: Mon, 25 May 2020 10:29:25 +0300 [thread overview]
Message-ID: <8d429d6b-81ee-0a28-8533-2e1d4faa6b37@gmail.com> (raw)
In-Reply-To: <20200523185755.8494-13-axboe@kernel.dk>
On 23/05/2020 21:57, Jens Axboe wrote:
> If the file is flagged with FMODE_BUF_RASYNC, then we don't have to punt
> the buffered read to an io-wq worker. Instead we can rely on page
> unlocking callbacks to support retry based async IO. This is a lot more
> efficient than doing async thread offload.
>
> The retry is done similarly to how we handle poll based retry. From
> the unlock callback, we simply queue the retry to a task_work based
> handler.
>
> Signed-off-by: Jens Axboe <axboe@kernel.dk>
> ---
> fs/io_uring.c | 99 +++++++++++++++++++++++++++++++++++++++++++++++++++
> 1 file changed, 99 insertions(+)
>
...
> +
> + init_task_work(&rw->task_work, io_async_buf_retry);
> + /* submit ref gets dropped, acquire a new one */
> + refcount_inc(&req->refs);
> + tsk = req->task;
> + ret = task_work_add(tsk, &rw->task_work, true);
> + if (unlikely(ret)) {
> + /* queue just for cancelation */
> + init_task_work(&rw->task_work, io_async_buf_cancel);
> + tsk = io_wq_get_task(req->ctx->io_wq);
IIRC, task will be put somewhere around io_free_req(). Then shouldn't here be
some juggling with reassigning req->task with task_{get,put}()?
> + task_work_add(tsk, &rw->task_work, true);
> + }
> + wake_up_process(tsk);
> + return 1;
> +}
...
> static int io_read(struct io_kiocb *req, bool force_nonblock)
> {
> struct iovec inline_vecs[UIO_FASTIOV], *iovec = inline_vecs;
> @@ -2601,6 +2696,7 @@ static int io_read(struct io_kiocb *req, bool force_nonblock)
> if (!ret) {
> ssize_t ret2;
>
> +retry:
> if (req->file->f_op->read_iter)
> ret2 = call_read_iter(req->file, kiocb, &iter);
> else
> @@ -2619,6 +2715,9 @@ static int io_read(struct io_kiocb *req, bool force_nonblock)
> if (!(req->flags & REQ_F_NOWAIT) &&
> !file_can_poll(req->file))
> req->flags |= REQ_F_MUST_PUNT;
> + if (io_rw_should_retry(req))
It looks like a state machine with IOCB_WAITQ and gotos. Wouldn't it be cleaner
to call call_read_iter()/loop_rw_iter() here directly instead of "goto retry" ?
BTW, can this async stuff return -EAGAIN ?
> + goto retry;
> + kiocb->ki_flags &= ~IOCB_WAITQ;
> return -EAGAIN;
> }
> }
>
--
Pavel Begunkov
next prev parent reply other threads:[~2020-05-25 7:30 UTC|newest]
Thread overview: 29+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-05-23 18:57 [PATCHSET v2 0/12] Add support for async buffered reads Jens Axboe
2020-05-23 18:57 ` [PATCH 01/12] block: read-ahead submission should imply no-wait as well Jens Axboe
2020-05-23 18:57 ` [PATCH 02/12] mm: allow read-ahead with IOCB_NOWAIT set Jens Axboe
2020-05-23 18:57 ` [PATCH 03/12] mm: abstract out wake_page_match() from wake_page_function() Jens Axboe
2020-05-23 18:57 ` [PATCH 04/12] mm: add support for async page locking Jens Axboe
2020-05-23 18:57 ` [PATCH 05/12] mm: support async buffered reads in generic_file_buffered_read() Jens Axboe
2020-05-24 14:05 ` Trond Myklebust
2020-05-24 16:30 ` Jens Axboe
2020-05-24 16:40 ` Jens Axboe
2020-05-24 17:11 ` Trond Myklebust
2020-05-24 17:12 ` Jens Axboe
2020-05-23 18:57 ` [PATCH 06/12] fs: add FMODE_BUF_RASYNC Jens Axboe
2020-05-23 18:57 ` [PATCH 07/12] ext4: flag as supporting buffered async reads Jens Axboe
2020-05-23 18:57 ` [PATCH 08/12] block: flag block devices as supporting IOCB_WAITQ Jens Axboe
2020-05-23 18:57 ` [PATCH 09/12] xfs: flag files as supporting buffered async reads Jens Axboe
2020-05-23 18:57 ` [PATCH 10/12] btrfs: " Jens Axboe
2020-05-23 18:57 ` [PATCH 11/12] mm: add kiocb_wait_page_queue_init() helper Jens Axboe
2020-05-23 18:57 ` [PATCH 12/12] io_uring: support true async buffered reads, if file provides it Jens Axboe
2020-05-25 7:29 ` Pavel Begunkov [this message]
2020-05-25 19:59 ` Jens Axboe
2020-05-26 7:44 ` Pavel Begunkov
2020-05-26 13:50 ` Jens Axboe
2020-05-26 7:38 ` Pavel Begunkov
2020-05-26 13:47 ` Jens Axboe
2020-05-23 19:20 ` [PATCHSET v2 0/12] Add support for async buffered reads Jens Axboe
2020-05-24 9:46 ` Chris Panayis
2020-05-24 19:24 ` Jens Axboe
2020-05-24 19:21 [PATCHSET v4 " Jens Axboe
2020-05-24 19:22 ` [PATCH 12/12] io_uring: support true async buffered reads, if file provides it Jens Axboe
2020-05-26 19:51 [PATCHSET v5 0/12] Add support for async buffered reads Jens Axboe
2020-05-26 19:51 ` [PATCH 12/12] io_uring: support true async buffered reads, if file provides it Jens Axboe
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