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,DKIM_ADSP_CUSTOM_MED, DKIM_INVALID,DKIM_SIGNED,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,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 CE541C2B9F8 for ; Tue, 25 May 2021 11:52:01 +0000 (UTC) Received: from gabe.freedesktop.org (gabe.freedesktop.org [131.252.210.177]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 9645061248 for ; Tue, 25 May 2021 11:52:01 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 9645061248 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=gmail.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=dri-devel-bounces@lists.freedesktop.org Received: from gabe.freedesktop.org (localhost [127.0.0.1]) by gabe.freedesktop.org (Postfix) with ESMTP id 063526E0E7; Tue, 25 May 2021 11:51:59 +0000 (UTC) Received: from mail-pl1-x634.google.com (mail-pl1-x634.google.com [IPv6:2607:f8b0:4864:20::634]) by gabe.freedesktop.org (Postfix) with ESMTPS id AA2E76E9FD; Tue, 25 May 2021 11:51:50 +0000 (UTC) Received: by mail-pl1-x634.google.com with SMTP id a7so7529962plh.3; Tue, 25 May 2021 04:51:50 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to; bh=b+pvn2nXkSIJnrU7EGg7e76c9ZIrOlzh6tmn2/UaWAc=; b=ux/BjJOENvYmKF+ItVg8NVlJLXaqpULPGGtnzWVllw854nwWBHJtg7js6S0+4puWIT HNFk7FvLe6A5F4iSNA18uI+QwuYBI6cstX2kp6/jFPpHIWZdNLOyKm0v0zdbWVp0nKI6 HqR4ofzG4AqYFMUnPPUM8HXxA7uzIl1hif+FJ/NNcv0XZMXnIM8V5AqQHqWwGZzomiRw 3nryiUCt0I7ipoDmFjFB+XowZ+AeazKQGBOvY+51jezOPJxSVT++LWMbjlc9kwKkoOnB UN6CQFWOghl8Cb/qWvrTgU76fuRlCqvt25hSfMfxZm3nmOBOHI66kRc6nyQLiYuKA9g8 Svkg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to; bh=b+pvn2nXkSIJnrU7EGg7e76c9ZIrOlzh6tmn2/UaWAc=; b=oqV6Ipte2VxW5XRj44LeiT9A7in6tt5Dk8zvB95xpMbQW5px8m38TPISsBc0IXCY7l itHYM2Yq9PvsRhdV12HmuN1n2/evxbqmoz3lImzz0dyc4DzvzjjfnR2+nh03D8i08gAE gaAcF9xJFNYt0UsN39X8edlysYELPaXnlvVgWXM3N3cWzD3mBDISLnMDC8Z926vOremO 5T30TwiHW3Kq2druXTJaqEhPY1JCrkLK+geR9gXzYu3xRblxA0H+rhhWW+G2IjuXg9nB PpmdvKAAILhBlTcBBTIykunFjwKtsLgi5szto9YwQOht42PCOFS51OJMYrO3lRfy4beP qkxw== X-Gm-Message-State: AOAM532pTJqBaCn+X0zIiFxw5bMZeFq5rGFW6VWy7ofD+SXjPdDHQ5f8 1Z8tB/5jrrV4uRvw6Wm/twM= X-Google-Smtp-Source: ABdhPJz6/UGyoOENAI29h279nKb1UeFwzFTVYdRAISes6uazmeV+8/t7UzyopHxY49DpGs0pQGb9UQ== X-Received: by 2002:a17:902:6b84:b029:ee:f966:1911 with SMTP id p4-20020a1709026b84b02900eef9661911mr29965113plk.69.1621943509655; Tue, 25 May 2021 04:51:49 -0700 (PDT) Received: from localhost (14-200-114-182.static.tpgi.com.au. [14.200.114.182]) by smtp.gmail.com with ESMTPSA id lj13sm1908099pjb.3.2021.05.25.04.51.46 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 25 May 2021 04:51:47 -0700 (PDT) Date: Tue, 25 May 2021 21:51:44 +1000 From: Balbir Singh To: Andrew Morton Subject: Re: [PATCH v9 07/10] mm: Device exclusive memory access Message-ID: References: <20210524132725.12697-1-apopple@nvidia.com> <20210524132725.12697-8-apopple@nvidia.com> <20210524151157.2dc5d2bb510ff86dc449bf0c@linux-foundation.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210524151157.2dc5d2bb510ff86dc449bf0c@linux-foundation.org> X-BeenThere: dri-devel@lists.freedesktop.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Direct Rendering Infrastructure - Development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: rcampbell@nvidia.com, willy@infradead.org, linux-doc@vger.kernel.org, nouveau@lists.freedesktop.org, Alistair Popple , hughd@google.com, linux-kernel@vger.kernel.org, dri-devel@lists.freedesktop.org, hch@infradead.org, linux-mm@kvack.org, jglisse@redhat.com, bskeggs@redhat.com, jgg@nvidia.com, jhubbard@nvidia.com, peterx@redhat.com, Christoph Hellwig Errors-To: dri-devel-bounces@lists.freedesktop.org Sender: "dri-devel" On Mon, May 24, 2021 at 03:11:57PM -0700, Andrew Morton wrote: > On Mon, 24 May 2021 23:27:22 +1000 Alistair Popple wrote: > > > Some devices require exclusive write access to shared virtual > > memory (SVM) ranges to perform atomic operations on that memory. This > > requires CPU page tables to be updated to deny access whilst atomic > > operations are occurring. > > > > In order to do this introduce a new swap entry > > type (SWP_DEVICE_EXCLUSIVE). When a SVM range needs to be marked for > > exclusive access by a device all page table mappings for the particular > > range are replaced with device exclusive swap entries. This causes any > > CPU access to the page to result in a fault. > > > > Faults are resovled by replacing the faulting entry with the original > > mapping. This results in MMU notifiers being called which a driver uses > > to update access permissions such as revoking atomic access. After > > notifiers have been called the device will no longer have exclusive > > access to the region. > > > > Walking of the page tables to find the target pages is handled by > > get_user_pages() rather than a direct page table walk. A direct page > > table walk similar to what migrate_vma_collect()/unmap() does could also > > have been utilised. However this resulted in more code similar in > > functionality to what get_user_pages() provides as page faulting is > > required to make the PTEs present and to break COW. > > > > ... > > > > Documentation/vm/hmm.rst | 17 ++++ > > include/linux/mmu_notifier.h | 6 ++ > > include/linux/rmap.h | 4 + > > include/linux/swap.h | 7 +- > > include/linux/swapops.h | 44 ++++++++- > > mm/hmm.c | 5 + > > mm/memory.c | 128 +++++++++++++++++++++++- > > mm/mprotect.c | 8 ++ > > mm/page_vma_mapped.c | 9 +- > > mm/rmap.c | 186 +++++++++++++++++++++++++++++++++++ > > 10 files changed, 405 insertions(+), 9 deletions(-) > > > > This is quite a lot of code added to core MM for a single driver. > > Is there any expectation that other drivers will use this code? > > Is there a way of reducing the impact (code size, at least) for systems > which don't need this code? > > How beneficial is this code to nouveau users? I see that it permits a > part of OpenCL to be implemented, but how useful/important is this in > the real world? That is a very good question! I've not reviewed the code, but a sample program with the described use case would make things easy to parse. I suspect that is not easy to build at the moment? I wonder how we co-ordinate all the work the mm is doing, page migration, reclaim with device exclusive access? Do we have any numbers for the worst case page fault latency when something is marked away for exclusive access? I presume for now this is anonymous memory only? SWP_DEVICE_EXCLUSIVE would only impact the address space of programs using the GPU. Should the exclusively marked range live in the unreclaimable list and recycled back to active/in-active to account for the fact that 1. It is not reclaimable and reclaim will only hurt via page faults? 2. It ages the page correctly or at-least allows for that possibility when the page is used by the GPU. Balbir Singh.