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Sun, 27 Oct 2019 12:17:42 -0700 (PDT) Received: from [192.168.43.222] ([109.126.132.16]) by smtp.gmail.com with ESMTPSA id p12sm8966934wrt.7.2019.10.27.12.17.41 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Sun, 27 Oct 2019 12:17:42 -0700 (PDT) Subject: Re: [PATCH 0/2][for-next] cleanup submission path To: Jens Axboe , linux-block@vger.kernel.org, linux-kernel@vger.kernel.org References: <666ed447-ba8f-29e7-237f-de8044aa63ea@kernel.dk> <5ec9bd14-d8f2-32e6-7f25-0ca7256c408a@gmail.com> <57db9960-0b31-9f40-c13b-1db6dcc88920@gmail.com> <02a25d12-1f44-de18-f233-b5421c608469@kernel.dk> <63f93f8a-4207-3ac4-a301-4907882009c9@gmail.com> <728dec9c-465c-2341-d7b5-929a50400e9c@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== Message-ID: <3b8b84d0-cde2-6bb0-c903-a1d71f9b83e2@gmail.com> Date: Sun, 27 Oct 2019 22:17:34 +0300 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.1.1 MIME-Version: 1.0 In-Reply-To: <728dec9c-465c-2341-d7b5-929a50400e9c@kernel.dk> Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="kP4hwIaGn6GdQ4ijPDmqXMwGoX0Pxxviy" Sender: linux-block-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org This is an OpenPGP/MIME signed message (RFC 4880 and 3156) --kP4hwIaGn6GdQ4ijPDmqXMwGoX0Pxxviy Content-Type: multipart/mixed; boundary="QK5GLNxwTN9ZtXPjaRlDGaVhxJjmv9gVZ"; protected-headers="v1" From: Pavel Begunkov To: Jens Axboe , linux-block@vger.kernel.org, linux-kernel@vger.kernel.org Message-ID: <3b8b84d0-cde2-6bb0-c903-a1d71f9b83e2@gmail.com> Subject: Re: [PATCH 0/2][for-next] cleanup submission path References: <666ed447-ba8f-29e7-237f-de8044aa63ea@kernel.dk> <5ec9bd14-d8f2-32e6-7f25-0ca7256c408a@gmail.com> <57db9960-0b31-9f40-c13b-1db6dcc88920@gmail.com> <02a25d12-1f44-de18-f233-b5421c608469@kernel.dk> <63f93f8a-4207-3ac4-a301-4907882009c9@gmail.com> <728dec9c-465c-2341-d7b5-929a50400e9c@kernel.dk> In-Reply-To: <728dec9c-465c-2341-d7b5-929a50400e9c@kernel.dk> --QK5GLNxwTN9ZtXPjaRlDGaVhxJjmv9gVZ Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: quoted-printable On 27/10/2019 22:02, Jens Axboe wrote: > On 10/27/19 12:56 PM, Pavel Begunkov wrote: >> On 27/10/2019 20:26, Jens Axboe wrote: >>> On 10/27/19 11:19 AM, Pavel Begunkov wrote: >>>> On 27/10/2019 19:56, Jens Axboe wrote: >>>>> On 10/27/19 10:49 AM, Jens Axboe wrote: >>>>>> On 10/27/19 10:44 AM, Pavel Begunkov wrote: >>>>>>> On 27/10/2019 19:32, Jens Axboe wrote: >>>>>>>> On 10/27/19 9:35 AM, Pavel Begunkov wrote: >>>>>>>>> A small cleanup of very similar but diverged io_submit_sqes() a= nd >>>>>>>>> io_ring_submit() >>>>>>>>> >>>>>>>>> Pavel Begunkov (2): >>>>>>>>> io_uring: handle mm_fault outside of submission >>>>>>>>> io_uring: merge io_submit_sqes and io_ring_submit >>>>>>>>> >>>>>>>>> fs/io_uring.c | 116 ++++++++++++++-----------------------= ------------- >>>>>>>>> 1 file changed, 33 insertions(+), 83 deletions(-) >>>>>>>> >>>>>>>> I like the cleanups here, but one thing that seems off is the >>>>>>>> assumption that io_sq_thread() always needs to grab the mm. If >>>>>>>> the sqes processed are just READ/WRITE_FIXED, then it never need= s >>>>>>>> to grab the mm. >>>>>>>> Yeah, we removed it to fix bugs. Personally, I think it would be= >>>>>>> clearer to do lazy grabbing conditionally, rather than have two >>>>>>> functions. And in this case it's easier to do after merging. >>>>>>> >>>>>>> Do you prefer to return it back first? >>>>>> >>>>>> Ah I see, no I don't care about that. >>>>> >>>>> OK, looked at the post-patches state. It's still not correct. You a= re >>>>> grabbing the mm from io_sq_thread() unconditionally. We should not = do >>>>> that, only if the sqes we need to submit need mm context. >>>>> >>>> That's what my question to the fix was about :) >>>> 1. Then, what the case it could fail? >>>> 2. Is it ok to hold it while polling? It could keep it for quite >>>> a long time if host is swift, e.g. submit->poll->submit->poll-> ... >>>> >>>> Anyway, I will add it back and resend the patchset. >>> >>> If possible in a simple way, I'd prefer if we do it as a prep patch a= nd >>> then queue that up for 5.4 since we now lost that optimization. Then= >>> layer the other 2 on top of that, since I'll just rebase the 5.5 stuf= f >>> on top of that. >>> >>> If not trivially possible for 5.4, then we'll just have to leave with= it >>> in that release. For that case, you can fold the change in with these= >>> two patches. >>> >> Hmm, what's the semantics? I think we should fail only those who need >> mm, but can't get it. The alternative is to fail all subsequent after >> the first mm_fault. >=20 > For the sqthread setup, there's no notion of "do this many". It just > grabs whatever it can and issues it. This means that the mm assign > is really per-sqe. What we did before, with the batching, just optimize= d > it so we'd only grab it for one batch IFF at least one sqe in that batc= h > needed the mm. >=20 > Since you've killed the batching, I think the logic should be something= > ala: >=20 > if (io_sqe_needs_user(sqe) && !cur_mm)) { > if (already_attempted_mmget_and_failed_ { > -EFAULT end sqe > } else { > do mm_get and mmuse dance > } > } >=20 > Hence if the sqe doesn't need the mm, doesn't matter if we previously > failed. If we need the mm and previously failed, -EFAULT. >=20 That makes sense, but a bit hard to implement honoring links and drains=20 --=20 Yours sincerely, Pavel Begunkov --QK5GLNxwTN9ZtXPjaRlDGaVhxJjmv9gVZ-- --kP4hwIaGn6GdQ4ijPDmqXMwGoX0Pxxviy Content-Type: application/pgp-signature; name="signature.asc" Content-Description: OpenPGP digital signature Content-Disposition: attachment; filename="signature.asc" -----BEGIN PGP SIGNATURE----- iQIzBAEBCAAdFiEE+6JuPTjTbx479o3OWt5b1Glr+6UFAl217U4ACgkQWt5b1Glr +6XWAA/+OZ4ye6Xxgf03JzgJEdG/lmvV9Yquv5Aeh6nGf+3QCj7iCWZ4dkWFkRsb ub45a/8wEEf8F4NgJwbH0U2zfeKUthzGBJXGgnIXveoSo3xZJYWUhiXMOukC32CZ yVUDIUCuj/htN+Gao1D+2EeFBsiNuEKSem+4vmq6Jo6m3ITleDWv5V7tJiT0ANpT dwHeFldqvZXd9L+iZmH4S5HDqMQWk2gZjYfmahbOD6qmuPrUeGpfiGkeNxCI3c2E 1ubZgVGSBKbiEg7zSFpsdSBsIJCXSiuCKaK9gzgZy4MD4g3lXmgPvFVpfuOXzo2A 5xDnAH1/J2pSY3v+EwIA+Fsoa4cZ+u6h/iUz2FZNpjNqcIViv6AQfgsDVwN0fXnE f54AgU+DougnsE9nhtV4hIzfvfQuGZKH6fchpuMGWquhwEE7wVHGemxVyg3UHO1N 7uEF5M3bRpt0cv7QADsbDt7bdBoiGAHT6Kdf7eNRGQ/HxriKmD9GNtjcsx++3tUI Exv6H0XdK1+f4ggKamxIcFWycY7f6KXsi9S2CGtJ5eZ4dTsk7nyoAFmr6Kth3vS5 7dSsm2iaZlXME8m3bTFeGtxruF90EaiTcdV69DH58tUPRoYlEHPXulzJlD01RwLp /o5ofqt/caY2cXb3mrsnLUzKh1sSjLd54PCxk2uYh8vKenqU+9k= =M3RG -----END PGP SIGNATURE----- --kP4hwIaGn6GdQ4ijPDmqXMwGoX0Pxxviy--