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=-5.5 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE, SPF_PASS,URIBL_BLOCKED,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 B6131C433E0 for ; Tue, 9 Feb 2021 12:20:35 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 9C73F64EAC for ; Tue, 9 Feb 2021 12:20:34 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 9C73F64EAC Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=hisilicon.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id E247F6B0005; Tue, 9 Feb 2021 07:20:33 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id DACFC6B006C; Tue, 9 Feb 2021 07:20:33 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id C74B86B006E; Tue, 9 Feb 2021 07:20:33 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0183.hostedemail.com [216.40.44.183]) by kanga.kvack.org (Postfix) with ESMTP id AEEE76B0005 for ; Tue, 9 Feb 2021 07:20:33 -0500 (EST) Received: from smtpin23.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay03.hostedemail.com (Postfix) with ESMTP id 64E8A8248047 for ; Tue, 9 Feb 2021 12:20:33 +0000 (UTC) X-FDA: 77798637546.23.tooth88_260635327607 Received: from filter.hostedemail.com (10.5.16.251.rfc1918.com [10.5.16.251]) by smtpin23.hostedemail.com (Postfix) with ESMTP id 4295837604 for ; Tue, 9 Feb 2021 12:20:33 +0000 (UTC) X-HE-Tag: tooth88_260635327607 X-Filterd-Recvd-Size: 4549 Received: from szxga07-in.huawei.com (szxga07-in.huawei.com [45.249.212.35]) by imf38.hostedemail.com (Postfix) with ESMTP for ; Tue, 9 Feb 2021 12:20:31 +0000 (UTC) Received: from DGGEMS405-HUB.china.huawei.com (unknown [172.30.72.58]) by szxga07-in.huawei.com (SkyGuard) with ESMTP id 4DZhlD3HWsz7jM7; Tue, 9 Feb 2021 20:19:04 +0800 (CST) Received: from [127.0.0.1] (10.40.188.87) by DGGEMS405-HUB.china.huawei.com (10.3.19.205) with Microsoft SMTP Server id 14.3.498.0; Tue, 9 Feb 2021 20:20:18 +0800 Subject: Re: [RFC PATCH v3 1/2] mempinfd: Add new syscall to provide memory pin To: Greg KH References: <1612685884-19514-2-git-send-email-wangzhou1@hisilicon.com> <2e6cf99f-beb6-9bef-1316-5e58fb0aa86e@hisilicon.com> CC: Andy Lutomirski , , , , , , "Andrew Morton" , Alexander Viro , , , , , , , , Sihang Chen From: Zhou Wang Message-ID: <2237506a-0c98-7ba6-5d5f-b60b637174c5@hisilicon.com> Date: Tue, 9 Feb 2021 20:20:18 +0800 User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:45.0) Gecko/20100101 Thunderbird/45.7.1 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset="utf-8" X-Originating-IP: [10.40.188.87] X-CFilter-Loop: Reflected Content-Transfer-Encoding: quoted-printable X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On 2021/2/9 20:01, Greg KH wrote: > On Tue, Feb 09, 2021 at 07:58:15PM +0800, Zhou Wang wrote: >> On 2021/2/9 17:37, Greg KH wrote: >>> On Tue, Feb 09, 2021 at 05:17:46PM +0800, Zhou Wang wrote: >>>> On 2021/2/8 6:02, Andy Lutomirski wrote: >>>>> >>>>> >>>>>> On Feb 7, 2021, at 12:31 AM, Zhou Wang w= rote: >>>>>> >>>>>> =EF=BB=BFSVA(share virtual address) offers a way for device to sha= re process virtual >>>>>> address space safely, which makes more convenient for user space d= evice >>>>>> driver coding. However, IO page faults may happen when doing DMA >>>>>> operations. As the latency of IO page fault is relatively big, DMA >>>>>> performance will be affected severely when there are IO page fault= s. >>>>>> From a long term view, DMA performance will be not stable. >>>>>> >>>>>> In high-performance I/O cases, accelerators might want to perform >>>>>> I/O on a memory without IO page faults which can result in dramati= cally >>>>>> increased latency. Current memory related APIs could not achieve t= his >>>>>> requirement, e.g. mlock can only avoid memory to swap to backup de= vice, >>>>>> page migration can still trigger IO page fault. >>>>>> >>>>>> Various drivers working under traditional non-SVA mode are using >>>>>> their own specific ioctl to do pin. Such ioctl can be seen in v4l2= , >>>>>> gpu, infiniband, media, vfio, etc. Drivers are usually doing dma >>>>>> mapping while doing pin. >>>>>> >>>>>> But, in SVA mode, pin could be a common need which isn't necessari= ly >>>>>> bound with any drivers, and neither is dma mapping needed by drive= rs >>>>>> since devices are using the virtual address of CPU. Thus, It is be= tter >>>>>> to introduce a new common syscall for it. >>>>>> >>>>>> This patch leverages the design of userfaultfd and adds mempinfd f= or pin >>>>>> to avoid messing up mm_struct. A fd will be got by mempinfd, then = user >>>>>> space can do pin/unpin pages by ioctls of this fd, all pinned page= s under >>>>>> one file will be unpinned in file release process. Like pin page c= ases in >>>>>> other places, can_do_mlock is used to check permission and input >>>>>> parameters. >>>>> >>>>> >>>>> Can you document what the syscall does? >>>> >>>> Will add related document in Documentation/vm. >>> >>> A manpage is always good, and will be required eventually :) >> >> manpage is maintained in another repo. Do you mean add a manpage >> patch in this series? >=20 > It's good to show how it will be used, don't you think? Agree, will add it in next version. Thanks, Zhou >=20 > thanks, >=20 > greg k-h >=20 > . >=20