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=-6.3 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,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 23957C433DB for ; Tue, 9 Feb 2021 12:04:51 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id DC13364E6F for ; Tue, 9 Feb 2021 12:04:50 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230165AbhBIMEt (ORCPT ); Tue, 9 Feb 2021 07:04:49 -0500 Received: from mail.kernel.org ([198.145.29.99]:53234 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229742AbhBIMCo (ORCPT ); Tue, 9 Feb 2021 07:02:44 -0500 Received: by mail.kernel.org (Postfix) with ESMTPSA id C2DDC64E16; Tue, 9 Feb 2021 12:01:56 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1612872117; bh=KXnFUWkeE3RzAL45lDxdFx/y1wzKceAzbuyX52i4TsI=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=DOTJHzzs0FAsJ9XZl1aGZ5cH8m8J6FlrUnzLTsv+HQsJPyoVjmCXhXEjUCceVUmNA mm29z79OAsLiQ013RWN+KhCvGh3r5fqgAyfLkqw+sPpEldf1l3bGpk7z8NvUTcBD9x gD47PEY6W2LOY6R2YitBTaNoniiO/UE5cclIXM40= Date: Tue, 9 Feb 2021 13:01:23 +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 Content-Transfer-Encoding: 8bit In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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 wrote: > >>>> > >>>> SVA(share virtual address) offers a way for device to share process virtual > >>>> address space safely, which makes more convenient for user space device > >>>> 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 dramatically > >>>> increased latency. Current memory related APIs could not achieve this > >>>> requirement, e.g. mlock can only avoid memory to swap to backup device, > >>>> 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 better > >>>> 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 user > >>>> 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 cases 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? It's good to show how it will be used, don't you think? thanks, greg k-h