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Tue, 26 May 2020 00:45:15 -0700 (PDT) To: Jens Axboe , io-uring@vger.kernel.org Cc: linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org References: <20200523185755.8494-1-axboe@kernel.dk> <20200523185755.8494-13-axboe@kernel.dk> <8d429d6b-81ee-0a28-8533-2e1d4faa6b37@gmail.com> <717e474a-5168-8e1e-2e02-c1bdff007bd9@kernel.dk> From: Pavel Begunkov Autocrypt: addr=asml.silence@gmail.com; prefer-encrypt=mutual; keydata= mQINBFmKBOQBEAC76ZFxLAKpDw0bKQ8CEiYJRGn8MHTUhURL02/7n1t0HkKQx2K1fCXClbps bdwSHrhOWdW61pmfMbDYbTj6ZvGRvhoLWfGkzujB2wjNcbNTXIoOzJEGISHaPf6E2IQx1ik9 6uqVkK1OMb7qRvKH0i7HYP4WJzYbEWVyLiAxUj611mC9tgd73oqZ2pLYzGTqF2j6a/obaqha +hXuWTvpDQXqcOZJXIW43atprH03G1tQs7VwR21Q1eq6Yvy2ESLdc38EqCszBfQRMmKy+cfp W3U9Mb1w0L680pXrONcnlDBCN7/sghGeMHjGKfNANjPc+0hzz3rApPxpoE7HC1uRiwC4et83 CKnncH1l7zgeBT9Oa3qEiBlaa1ZCBqrA4dY+z5fWJYjMpwI1SNp37RtF8fKXbKQg+JuUjAa9 Y6oXeyEvDHMyJYMcinl6xCqCBAXPHnHmawkMMgjr3BBRzODmMr+CPVvnYe7BFYfoajzqzq+h EyXSl3aBf0IDPTqSUrhbmjj5OEOYgRW5p+mdYtY1cXeK8copmd+fd/eTkghok5li58AojCba jRjp7zVOLOjDlpxxiKhuFmpV4yWNh5JJaTbwCRSd04sCcDNlJj+TehTr+o1QiORzc2t+N5iJ NbILft19Izdn8U39T5oWiynqa1qCLgbuFtnYx1HlUq/HvAm+kwARAQABtDFQYXZlbCBCZWd1 bmtvdiAoc2lsZW5jZSkgPGFzbWwuc2lsZW5jZUBnbWFpbC5jb20+iQJOBBMBCAA4FiEE+6Ju PTjTbx479o3OWt5b1Glr+6UFAlmKBOQCGwMFCwkIBwIGFQgJCgsCBBYCAwECHgECF4AACgkQ Wt5b1Glr+6WxZA//QueaKHzgdnOikJ7NA/Vq8FmhRlwgtP0+E+w93kL+ZGLzS/cUCIjn2f4Q Mcutj2Neg0CcYPX3b2nJiKr5Vn0rjJ/suiaOa1h1KzyNTOmxnsqE5fmxOf6C6x+NKE18I5Jy xzLQoktbdDVA7JfB1itt6iWSNoOTVcvFyvfe5ggy6FSCcP+m1RlR58XxVLH+qlAvxxOeEr/e aQfUzrs7gqdSd9zQGEZo0jtuBiB7k98t9y0oC9Jz0PJdvaj1NZUgtXG9pEtww3LdeXP/TkFl HBSxVflzeoFaj4UAuy8+uve7ya/ECNCc8kk0VYaEjoVrzJcYdKP583iRhOLlZA6HEmn/+Gh9 4orG67HNiJlbFiW3whxGizWsrtFNLsSP1YrEReYk9j1SoUHHzsu+ZtNfKuHIhK0sU07G1OPN 2rDLlzUWR9Jc22INAkhVHOogOcc5ajMGhgWcBJMLCoi219HlX69LIDu3Y34uIg9QPZIC2jwr 24W0kxmK6avJr7+n4o8m6sOJvhlumSp5TSNhRiKvAHB1I2JB8Q1yZCIPzx+w1ALxuoWiCdwV M/azguU42R17IuBzK0S3hPjXpEi2sK/k4pEPnHVUv9Cu09HCNnd6BRfFGjo8M9kZvw360gC1 reeMdqGjwQ68o9x0R7NBRrtUOh48TDLXCANAg97wjPoy37dQE7e5Ag0EWYoE5AEQAMWS+aBV IJtCjwtfCOV98NamFpDEjBMrCAfLm7wZlmXy5I6o7nzzCxEw06P2rhzp1hIqkaab1kHySU7g dkpjmQ7Jjlrf6KdMP87mC/Hx4+zgVCkTQCKkIxNE76Ff3O9uTvkWCspSh9J0qPYyCaVta2D1 Sq5HZ8WFcap71iVO1f2/FEHKJNz/YTSOS/W7dxJdXl2eoj3gYX2UZNfoaVv8OXKaWslZlgqN jSg9wsTv1K73AnQKt4fFhscN9YFxhtgD/SQuOldE5Ws4UlJoaFX/yCoJL3ky2kC0WFngzwRF Yo6u/KON/o28yyP+alYRMBrN0Dm60FuVSIFafSqXoJTIjSZ6olbEoT0u17Rag8BxnxryMrgR dkccq272MaSS0eOC9K2rtvxzddohRFPcy/8bkX+t2iukTDz75KSTKO+chce62Xxdg62dpkZX xK+HeDCZ7gRNZvAbDETr6XI63hPKi891GeZqvqQVYR8e+V2725w+H1iv3THiB1tx4L2bXZDI DtMKQ5D2RvCHNdPNcZeldEoJwKoA60yg6tuUquvsLvfCwtrmVI2rL2djYxRfGNmFMrUDN1Xq F3xozA91q3iZd9OYi9G+M/OA01husBdcIzj1hu0aL+MGg4Gqk6XwjoSxVd4YT41kTU7Kk+/I 5/Nf+i88ULt6HanBYcY/+Daeo/XFABEBAAGJAjYEGAEIACAWIQT7om49ONNvHjv2jc5a3lvU aWv7pQUCWYoE5AIbDAAKCRBa3lvUaWv7pfmcEACKTRQ28b1y5ztKuLdLr79+T+LwZKHjX++P 4wKjEOECCcB6KCv3hP+J2GCXDOPZvdg/ZYZafqP68Yy8AZqkfa4qPYHmIdpODtRzZSL48kM8 LRzV8Rl7J3ItvzdBRxf4T/Zseu5U6ELiQdCUkPGsJcPIJkgPjO2ROG/ZtYa9DvnShNWPlp+R uPwPccEQPWO/NP4fJl2zwC6byjljZhW5kxYswGMLBwb5cDUZAisIukyAa8Xshdan6C2RZcNs rB3L7vsg/R8UCehxOH0C+NypG2GqjVejNZsc7bgV49EOVltS+GmGyY+moIzxsuLmT93rqyII 5rSbbcTLe6KBYcs24XEoo49Zm9oDA3jYvNpeYD8rDcnNbuZh9kTgBwFN41JHOPv0W2FEEWqe JsCwQdcOQ56rtezdCJUYmRAt3BsfjN3Jn3N6rpodi4Dkdli8HylM5iq4ooeb5VkQ7UZxbCWt UVMKkOCdFhutRmYp0mbv2e87IK4erwNHQRkHUkzbsuym8RVpAZbLzLPIYK/J3RTErL6Z99N2 m3J6pjwSJY/zNwuFPs9zGEnRO4g0BUbwGdbuvDzaq6/3OJLKohr5eLXNU3JkT+3HezydWm3W OPhauth7W0db74Qd49HXK0xe/aPrK+Cp+kU1HRactyNtF8jZQbhMCC8vMGukZtWaAwpjWiiH bA== Subject: Re: [PATCH 12/12] io_uring: support true async buffered reads, if file provides it Message-ID: Date: Tue, 26 May 2020 10:44:00 +0300 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.3.0 MIME-Version: 1.0 In-Reply-To: <717e474a-5168-8e1e-2e02-c1bdff007bd9@kernel.dk> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 25/05/2020 22:59, Jens Axboe wrote: > On 5/25/20 1:29 AM, Pavel Begunkov wrote: >> 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 >>> --- >>> 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}()? > > Not sure I follow? Yes, we'll put this task again when the request > is freed, but not sure what you mean with juggling? I meant something like: ... /* queue just for cancelation */ init_task_work(&rw->task_work, io_async_buf_cancel); + put_task_struct(req->task); + req->task = get_task_struct(io_wq_task); but, thinking twice, if I got the whole idea right, it should be ok as is -- io-wq won't go away before the request anyway, and leaving req->task pinned down for a bit is not a problem. >>> + 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" ? > > We could, probably making that part a separate helper then. How about the > below incremental? IMHO, it was easy to get lost with such implicit state switching. Looks better now! See a small comment below. > >> BTW, can this async stuff return -EAGAIN ? > > Probably? Prefer not to make any definitive calls on that being possible or > not, as it's sure to disappoint. If it does and IOCB_WAITQ is already set, > then we'll punt to a thread like before. Sounds reasonable > > > diff --git a/fs/io_uring.c b/fs/io_uring.c > index a5a4d9602915..669dccd81207 100644 > --- a/fs/io_uring.c > +++ b/fs/io_uring.c > @@ -2677,6 +2677,13 @@ static bool io_rw_should_retry(struct io_kiocb *req) > return false; > } > > +static int __io_read(struct io_kiocb *req, struct iov_iter *iter) > +{ > + if (req->file->f_op->read_iter) > + return call_read_iter(req->file, &req->rw.kiocb, iter); > + return loop_rw_iter(READ, req->file, &req->rw.kiocb, iter); > +} > + > static int io_read(struct io_kiocb *req, bool force_nonblock) > { > struct iovec inline_vecs[UIO_FASTIOV], *iovec = inline_vecs; > @@ -2710,11 +2717,7 @@ 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 > - ret2 = loop_rw_iter(READ, req->file, kiocb, &iter); > + ret2 = __io_read(req, &iter); > > /* Catch -EAGAIN return for forced non-blocking submission */ > if (!force_nonblock || ret2 != -EAGAIN) { > @@ -2729,8 +2732,11 @@ 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)) > - goto retry; > + if (io_rw_should_retry(req)) { > + ret2 = __io_read(req, &iter); > + if (ret2 != -EAGAIN) > + goto out_free; "goto out_free" returns ret=0, so someone should add a cqe if (ret2 != -EAGAIN) { kiocb_done(kiocb, ret2); goto free_out; } > + } > kiocb->ki_flags &= ~IOCB_WAITQ; > return -EAGAIN; > } > -- Pavel Begunkov