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=-6.8 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,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 1C0F4C4727E for ; Tue, 22 Sep 2020 00:01:24 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id A79DC207C4 for ; Tue, 22 Sep 2020 00:01:23 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=nvidia.com header.i=@nvidia.com header.b="Vc3t6sR2" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org A79DC207C4 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=nvidia.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 02A30900008; Mon, 21 Sep 2020 20:01:23 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id F1C6D900004; Mon, 21 Sep 2020 20:01:22 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id E3247900008; Mon, 21 Sep 2020 20:01:22 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0022.hostedemail.com [216.40.44.22]) by kanga.kvack.org (Postfix) with ESMTP id CD4E5900004 for ; Mon, 21 Sep 2020 20:01:22 -0400 (EDT) Received: from smtpin12.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay01.hostedemail.com (Postfix) with ESMTP id 76997180AD801 for ; Tue, 22 Sep 2020 00:01:22 +0000 (UTC) X-FDA: 77288742804.12.book19_2c10c9627149 Received: from filter.hostedemail.com (10.5.16.251.rfc1918.com [10.5.16.251]) by smtpin12.hostedemail.com (Postfix) with ESMTP id 2E5C0180039F4 for ; Tue, 22 Sep 2020 00:01:22 +0000 (UTC) X-HE-Tag: book19_2c10c9627149 X-Filterd-Recvd-Size: 3938 Received: from hqnvemgate24.nvidia.com (hqnvemgate24.nvidia.com [216.228.121.143]) by imf11.hostedemail.com (Postfix) with ESMTP for ; Tue, 22 Sep 2020 00:01:21 +0000 (UTC) Received: from hqmail.nvidia.com (Not Verified[216.228.121.13]) by hqnvemgate24.nvidia.com (using TLS: TLSv1.2, AES256-SHA) id ; Mon, 21 Sep 2020 16:59:47 -0700 Received: from [10.2.52.174] (10.124.1.5) by HQMAIL107.nvidia.com (172.20.187.13) with Microsoft SMTP Server (TLS) id 15.0.1473.3; Tue, 22 Sep 2020 00:01:19 +0000 Subject: Re: [PATCH 1/5] mm: Introduce mm_struct.has_pinned From: John Hubbard To: Peter Xu , , CC: Jason Gunthorpe , Andrew Morton , Jan Kara , Michal Hocko , Kirill Tkhai , Kirill Shutemov , Hugh Dickins , Christoph Hellwig , Andrea Arcangeli , Oleg Nesterov , Leon Romanovsky , Linus Torvalds , "Jann Horn" References: <20200921211744.24758-1-peterx@redhat.com> <20200921211744.24758-2-peterx@redhat.com> <224908c1-5d0f-8e01-baa9-94ec2374971f@nvidia.com> Message-ID: <8bc86452-3a7e-c435-014b-5acc21f591d2@nvidia.com> Date: Mon, 21 Sep 2020 17:01:19 -0700 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.12.0 MIME-Version: 1.0 In-Reply-To: <224908c1-5d0f-8e01-baa9-94ec2374971f@nvidia.com> Content-Type: text/plain; charset="utf-8"; format=flowed Content-Language: en-US Content-Transfer-Encoding: quoted-printable X-Originating-IP: [10.124.1.5] X-ClientProxiedBy: HQMAIL105.nvidia.com (172.20.187.12) To HQMAIL107.nvidia.com (172.20.187.13) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=nvidia.com; s=n1; t=1600732787; bh=milZW06+puWuXJ7s4e6GxDGScmec4RaKsmWjlEMy2HQ=; h=Subject:From:To:CC:References:Message-ID:Date:User-Agent: MIME-Version:In-Reply-To:Content-Type:Content-Language: Content-Transfer-Encoding:X-Originating-IP:X-ClientProxiedBy; b=Vc3t6sR2NkFygwWMzI8HjNAGrQrTsSHZImME3dRZ1Iip17Dj0+riHdTiIKPb7QhJ2 nm8hsv/2R3+rFklud1O77an1P6U6LZSIQR+J/Qlyc9+VsPQGOqaG7wBR06umDU3DWw xpl3ycYaJJLcNXiUAa9u0VMC7E8cPJg1XNQWHXzXBl/B2c5hOK2xoVpBdFSgrs0fUN JlIPdxgbth/N+OvTIWLbdvtIPSeLC1Sqg6RScFaTNh2C/m4NT56Lmx2zYqLZDOUUd5 PvZ65qLKfEjDOYMsN6s0Mp/I58TSK71FTCqxmxRZNk7O4xGTgX9hVM41Qeec/MIN28 WqUBgWbwuPe0g== 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 9/21/20 4:53 PM, John Hubbard wrote: > On 9/21/20 2:17 PM, Peter Xu wrote: >> (Commit message collected from Jason Gunthorpe) >> >> Reduce the chance of false positive from page_maybe_dma_pinned() by keep= ing >=20 > Not yet, it doesn't. :)=C2=A0 More: >=20 >> track if the mm_struct has ever been used with pin_user_pages(). mm_stru= cts >> that have never been passed to pin_user_pages() cannot have a positive >> page_maybe_dma_pinned() by definition. This allows cases that might driv= e up >> the page ref_count to avoid any penalty from handling dma_pinned pages. >> >> Due to complexities with unpining this trivial version is a permanent st= icky >> bit, future work will be needed to make this a counter. >=20 > How about this instead: >=20 > Subsequent patches intend to reduce the chance of false positives from > page_maybe_dma_pinned(), by also considering whether or not a page has > even been part of an mm struct that has ever had pin_user_pages*() arggh, correction: please make that: "...whether or not a page is part of an mm struct that...". (Present tense.) Otherwise, people start wondering about the checkered past of a page's past lives, and it badly distracts from the main point here. :) thanks, --=20 John Hubbard NVIDIA