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=-3.5 required=3.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS,URIBL_BLOCKED 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 F21DDC433E0 for ; Tue, 9 Feb 2021 09:37:51 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 496F264E75 for ; Tue, 9 Feb 2021 09:37:51 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 496F264E75 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=linuxfoundation.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id A06E26B0005; Tue, 9 Feb 2021 04:37:50 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 9B7416B006C; Tue, 9 Feb 2021 04:37:50 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 87DF06B006E; Tue, 9 Feb 2021 04:37:50 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0093.hostedemail.com [216.40.44.93]) by kanga.kvack.org (Postfix) with ESMTP id 731296B0005 for ; Tue, 9 Feb 2021 04:37:50 -0500 (EST) Received: from smtpin30.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay02.hostedemail.com (Postfix) with ESMTP id 379BB144F0 for ; Tue, 9 Feb 2021 09:37:50 +0000 (UTC) X-FDA: 77798227500.30.crook82_3a065b427606 Received: from filter.hostedemail.com (10.5.16.251.rfc1918.com [10.5.16.251]) by smtpin30.hostedemail.com (Postfix) with ESMTP id 01A2918243081 for ; Tue, 9 Feb 2021 09:37:49 +0000 (UTC) X-HE-Tag: crook82_3a065b427606 X-Filterd-Recvd-Size: 3955 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by imf25.hostedemail.com (Postfix) with ESMTP for ; Tue, 9 Feb 2021 09:37:49 +0000 (UTC) Received: by mail.kernel.org (Postfix) with ESMTPSA id E804D64E27; Tue, 9 Feb 2021 09:37:47 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1612863468; bh=3uhgNxvkQ3DE4szNXNrRNOmM42w+TvFbEvvc39Kp9o8=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=dnM8UoIu7vjUquwOGgLNI/nFIs7c5cxhJzUlDrEgEcxaM71P1VbXUNr75slYvIvip JxniosSVimGPVVpFt1UW4dNP6DywhSeOr4E8K+/y/jp/U1BlN9NKoE4b81YZyYVsS4 TOZQ8fJ6UIH5YGUd0osrd5uxargdhmbZrAwT4234= Date: Tue, 9 Feb 2021 10:37:45 +0100 From: Greg KH To: Zhou Wang Cc: Andy Lutomirski , linux-kernel@vger.kernel.org, iommu@lists.linux-foundation.org, linux-mm@kvack.org, linux-arm-kernel@lists.infradead.org, linux-api@vger.kernel.org, Andrew Morton , Alexander Viro , song.bao.hua@hisilicon.com, jgg@ziepe.ca, kevin.tian@intel.com, jean-philippe@linaro.org, eric.auger@redhat.com, liguozhu@hisilicon.com, zhangfei.gao@linaro.org, Sihang Chen Subject: Re: [RFC PATCH v3 1/2] mempinfd: Add new syscall to provide memory pin Message-ID: References: <1612685884-19514-2-git-send-email-wangzhou1@hisilicon.com> <2e6cf99f-beb6-9bef-1316-5e58fb0aa86e@hisilicon.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <2e6cf99f-beb6-9bef-1316-5e58fb0aa86e@hisilicon.com> 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 Tue, Feb 09, 2021 at 05:17:46PM +0800, Zhou Wang wrote: > On 2021/2/8 6:02, Andy Lutomirski wrote: > >=20 > >=20 > >> On Feb 7, 2021, at 12:31 AM, Zhou Wang wro= te: > >> > >> =EF=BB=BFSVA(share virtual address) offers a way for device to share= process virtual > >> address space safely, which makes more convenient for user space dev= ice > >> 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 faults. > >> 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 dramatica= lly > >> increased latency. Current memory related APIs could not achieve thi= s > >> requirement, e.g. mlock can only avoid memory to swap to backup devi= ce, > >> 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 necessarily > >> bound with any drivers, and neither is dma mapping needed by drivers > >> since devices are using the virtual address of CPU. Thus, It is bett= er > >> to introduce a new common syscall for it. > >> > >> This patch leverages the design of userfaultfd and adds mempinfd for= pin > >> to avoid messing up mm_struct. A fd will be got by mempinfd, then us= er > >> space can do pin/unpin pages by ioctls of this fd, all pinned pages = under > >> one file will be unpinned in file release process. Like pin page cas= es in > >> other places, can_do_mlock is used to check permission and input > >> parameters. > >=20 > >=20 > > Can you document what the syscall does? >=20 > Will add related document in Documentation/vm. A manpage is always good, and will be required eventually :) thanks, greg k-h