From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-4.3 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE, SPF_PASS,USER_AGENT_SANE_1 autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 34C75C2BB9A for ; Tue, 15 Dec 2020 14:12:21 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 036B1224BE for ; Tue, 15 Dec 2020 14:12:21 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728283AbgLOOKW (ORCPT ); Tue, 15 Dec 2020 09:10:22 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:39296 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729275AbgLOOJn (ORCPT ); Tue, 15 Dec 2020 09:09:43 -0500 Received: from mail-wm1-x343.google.com (mail-wm1-x343.google.com [IPv6:2a00:1450:4864:20::343]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 9339AC061282; Tue, 15 Dec 2020 06:08:57 -0800 (PST) Received: by mail-wm1-x343.google.com with SMTP id a3so18612052wmb.5; Tue, 15 Dec 2020 06:08:57 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=to:cc:references:from:autocrypt:subject:message-id:date:user-agent :mime-version:in-reply-to:content-language:content-transfer-encoding; bh=IJwMYXZybCxJT0UHVVdIgfuOq3K54a+9Y/EpPWFpv/0=; b=eVXRaLFMJRqh7EtstSBOKNO6tJ4yUKa28N9ZGhkpLq+N+ciYCyvZRvn3XxjguI/U2M EzZt0wjil3zjy86ENb0suvcWF41egiXxNos6lkx4QCtSIzo4fphc7B6cLdGqoEURVrFf za8HjMp2ciqnBrlmRd8gaykyftQGs+vMA8Go7vb4SUIVu4sOI7GcY3QytCh5l9PbMxu4 IXiF1MbLfbZhMwd2CHQotw/NPedTmw+K35iWgewi5jT0ADKzvqeVB6WrbcrN/vsEOE/9 do9dykgLxRCJZEqKIYfezOahnF4eskXBTycj9Zja5KX+tsonMWdpgg1tL3kDBFiHWsl+ GPKQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:to:cc:references:from:autocrypt:subject :message-id:date:user-agent:mime-version:in-reply-to :content-language:content-transfer-encoding; bh=IJwMYXZybCxJT0UHVVdIgfuOq3K54a+9Y/EpPWFpv/0=; b=cBBDxdIABrugYb1DlhDNFaVB+/WhUE+ifPlSO2SDdFwTCKdwBZerYlrvWo3Sb42zrX CaUPWZXnWfAyyOTM/kEXr5IwpVlNn1vZSOGvDKCxfX+A+DL99RfyBYkfExkkclUh5PWO /pPggCxE34x0DohPJCWC4hXa1aD4WDg0PEtndC+alYWAOSK1w/sMhFZF59AgtI2sT7xf emqyzUmwrtzqtxKi/aqHUKcsuOGftKxnPbQB5a87Yv5yQ0lkNGk1e+0Q/n4HAeoWd56+ w8NPb3ZXIODzuGURZFVLIy2AVdGhBG9ytBalyDK/9QMualCr2oNXknpUYoh75kRlLgu8 +LvA== X-Gm-Message-State: AOAM531LPd61frw+jnHwDUON5F+JUd7MmWIHcFmAls7jU9h0qlbLMeSI usXgg3NbqzU9KSRDNfrhnIrvzA4BAJ3/4J7Y X-Google-Smtp-Source: ABdhPJyWDj2cYrF/oujgWz5P30oSEMUlwkpU/DSaAHrYgy/IZqHJpoXuaMOofStO5CgxkDkwCZ5VpQ== X-Received: by 2002:a1c:220a:: with SMTP id i10mr32886712wmi.93.1608041336013; Tue, 15 Dec 2020 06:08:56 -0800 (PST) Received: from [192.168.8.128] ([185.69.144.228]) by smtp.gmail.com with ESMTPSA id z8sm37038733wmg.17.2020.12.15.06.08.54 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 15 Dec 2020 06:08:54 -0800 (PST) To: Ming Lei Cc: linux-block@vger.kernel.org, Jens Axboe , Christoph Hellwig , Matthew Wilcox , Johannes Weiner , Alexander Viro , "Darrick J . Wong" , "Martin K . Petersen" , Jonathan Corbet , linux-xfs@vger.kernel.org, linux-fsdevel@vger.kernel.org, io-uring@vger.kernel.org, linux-kernel@vger.kernel.org, target-devel@vger.kernel.org, linux-scsi@vger.kernel.org, linux-doc@vger.kernel.org References: <20201215014114.GA1777020@T590> <103235c1-e7d0-0b55-65d0-013d1a09304e@gmail.com> <20201215120357.GA1798021@T590> 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 v1 0/6] no-copy bvec Message-ID: Date: Tue, 15 Dec 2020 14:05:35 +0000 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: <20201215120357.GA1798021@T590> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: io-uring@vger.kernel.org On 15/12/2020 12:03, Ming Lei wrote: > On Tue, Dec 15, 2020 at 11:14:20AM +0000, Pavel Begunkov wrote: >> On 15/12/2020 01:41, Ming Lei wrote: >>> On Tue, Dec 15, 2020 at 12:20:19AM +0000, Pavel Begunkov wrote: >>>> Instead of creating a full copy of iter->bvec into bio in direct I/O, >>>> the patchset makes use of the one provided. It changes semantics and >>>> obliges users of asynchronous kiocb to track bvec lifetime, and [1/6] >>>> converts the only place that doesn't. >>> >>> Just think of one corner case: iov_iter(BVEC) may pass bvec table with zero >>> length bvec, which may not be supported by block layer or driver, so >>> this patchset has to address this case first. >> >> The easiest for me would be to fallback to copy if there are zero bvecs, >> e.g. finding such during iov_iter_alignment(), but do we know from where >> zero bvecs can came? As it's internals we may want to forbid them if >> there is not too much hassle. > > You may find clue from the following link: > > https://www.mail-archive.com/linux-kernel@vger.kernel.org/msg2262077.html Thanks for the link! Al, you mentioned "Zero-length segments are not disallowed", do you have a strong opinion on that? Apart from already diverged behaviour from the block layer and getting in the way of this series, without it we'd also be able to remove some extra ifs, e.g. in iterate_bvec() -- Pavel Begunkov