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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 4735EC05027 for ; Mon, 23 Jan 2023 12:01:45 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231679AbjAWMBo (ORCPT ); Mon, 23 Jan 2023 07:01:44 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:46678 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231584AbjAWMBf (ORCPT ); Mon, 23 Jan 2023 07:01:35 -0500 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 369D3EB47 for ; Mon, 23 Jan 2023 04:00:54 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1674475253; h=from:from:reply-to:subject:subject:date:date:message-id:message-id:to: cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=6Okwn/a4YJNsJ0yzPfIHYIoNOHrMsUYtIsHnnkAfJ8M=; b=HltLphbJObN306c8f6fpvBVKH+6qAWSV/38vw6VJrh/l3HuIatwid1XN+ONj8Zm/XYf2e0 kSge43fUdbqfexOXk/aoq8877Gq1FItZDLUZ4Snx9hwhBMzrsDOG6h6NZ59FWnO3JQuif0 n5ZOVqxZEaPFJu+lCIukwtGcgusTqSc= Received: from mimecast-mx02.redhat.com (mimecast-mx02.redhat.com [66.187.233.88]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-197-UdwdbkYsMe6BQydYc7CUVA-1; Mon, 23 Jan 2023 07:00:49 -0500 X-MC-Unique: UdwdbkYsMe6BQydYc7CUVA-1 Received: from smtp.corp.redhat.com (int-mx10.intmail.prod.int.rdu2.redhat.com [10.11.54.10]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 7E6BB802BEE; Mon, 23 Jan 2023 12:00:48 +0000 (UTC) Received: from warthog.procyon.org.uk (unknown [10.33.36.23]) by smtp.corp.redhat.com (Postfix) with ESMTP id D0C3C492B02; Mon, 23 Jan 2023 12:00:46 +0000 (UTC) Organization: Red Hat UK Ltd. 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Registered in England and Wales under Company Registration No. 3798903 From: David Howells In-Reply-To: <3814749.1674474663@warthog.procyon.org.uk> References: <3814749.1674474663@warthog.procyon.org.uk> <246ba813-698b-8696-7f4d-400034a3380b@redhat.com> <20230120175556.3556978-1-dhowells@redhat.com> <20230120175556.3556978-3-dhowells@redhat.com> Cc: dhowells@redhat.com, David Hildenbrand , Al Viro , Christoph Hellwig , Matthew Wilcox , Jens Axboe , Jan Kara , Jeff Layton , Logan Gunthorpe , linux-fsdevel@vger.kernel.org, linux-block@vger.kernel.org, linux-kernel@vger.kernel.org, Christoph Hellwig , John Hubbard , linux-mm@kvack.org Subject: Re: [PATCH v7 2/8] iov_iter: Add a function to extract a page list from an iterator MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-ID: <3815848.1674475246.1@warthog.procyon.org.uk> Content-Transfer-Encoding: quoted-printable Date: Mon, 23 Jan 2023 12:00:46 +0000 Message-ID: <3815849.1674475246@warthog.procyon.org.uk> X-Scanned-By: MIMEDefang 3.1 on 10.11.54.10 To: unlisted-recipients:; (no To-header on input) Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org David Howells wrote: > > How does this work align with the goal of no longer using FOLL_GET for > > O_DIRECT? We should get rid of any FOLL_GET usage for accessing page c= ontent. > = > Would that run the risk of changes being made by the child being visible= to > the a DIO write if the parent changes the buffer first? > = > = > PARENT CHILD > =3D=3D=3D=3D=3D=3D =3D=3D=3D=3D=3D > start-DIO-write > fork() =3D pid fork() =3D 0 > alter-buffer > CoW happens > page copied original page retained > alter-buffer > Ah, I think I might have got the wrong end of the stick. A pinned page is *always* copied on fork() if I understand copy_present_pte() correctly. David 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 Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.lore.kernel.org (Postfix) with ESMTP id E3E94C38142 for ; Mon, 23 Jan 2023 12:00:59 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 4BECD6B0071; Mon, 23 Jan 2023 07:00:59 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 46E6C6B0072; Mon, 23 Jan 2023 07:00:59 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 35D896B0073; Mon, 23 Jan 2023 07:00:59 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0013.hostedemail.com [216.40.44.13]) by kanga.kvack.org (Postfix) with ESMTP id 247086B0071 for ; Mon, 23 Jan 2023 07:00:59 -0500 (EST) Received: from smtpin24.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay01.hostedemail.com (Postfix) with ESMTP id EC2161C5EC3 for ; Mon, 23 Jan 2023 12:00:58 +0000 (UTC) X-FDA: 80385922596.24.D7C6131 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) by imf02.hostedemail.com (Postfix) with ESMTP id 2353B80022 for ; Mon, 23 Jan 2023 12:00:55 +0000 (UTC) Authentication-Results: imf02.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b=E4WW8Zz+; spf=pass (imf02.hostedemail.com: domain of dhowells@redhat.com designates 170.10.129.124 as permitted sender) smtp.mailfrom=dhowells@redhat.com; dmarc=pass (policy=none) header.from=redhat.com ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1674475256; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=6Okwn/a4YJNsJ0yzPfIHYIoNOHrMsUYtIsHnnkAfJ8M=; b=TMuwHIYhRfWmDu2em6HcockkK63urzmVdvp9SYL1Oq8T24MEUpIO18KFuGatk8tIm8Kotu xEENMufyzrYyTFj0U1sL8eJeGK/9z6FrhNrFEFh8DywtbmWg7TqPTg4M0PwLw0QYC/O31r LRaTMjIzwiiuSmfBuENhjpu4A6V/nsA= ARC-Authentication-Results: i=1; imf02.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b=E4WW8Zz+; spf=pass (imf02.hostedemail.com: domain of dhowells@redhat.com designates 170.10.129.124 as permitted sender) smtp.mailfrom=dhowells@redhat.com; dmarc=pass (policy=none) header.from=redhat.com ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1674475256; a=rsa-sha256; cv=none; b=UA0m7KiUSQtnGgkAFM6WgnSwo6kQ4O/C0TyPilo8Pf7EdKlio8fTj5njNwfHzR7TTzKC+9 IBlBTIwOXgr8oxDt9Fti+kkYj8Pi1674Vjw4ksGj14amhmA+G44L+FS4w6GPtFfBdLDwi9 2crrcq/1KFRM/L5FTawGNKVK0nD3N6Y= DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1674475255; h=from:from:reply-to:subject:subject:date:date:message-id:message-id:to: cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=6Okwn/a4YJNsJ0yzPfIHYIoNOHrMsUYtIsHnnkAfJ8M=; b=E4WW8Zz+nf2hFHGNs6sU65Sqkcgy4tc5J+W6IPzK924fq7NdZ+GtfCme2TCJyFEGUpBn2H Yxcnq2JZpRNiMQDJtyAYVfKNhfNIUFKZnYvVyzBOhmyDWrFvsQCGVSA+vXd+UngcrcwdIH pkiiV6QC2FiD/0PsbSOd/3LNDcgVqE8= Received: from mimecast-mx02.redhat.com (mimecast-mx02.redhat.com [66.187.233.88]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-197-UdwdbkYsMe6BQydYc7CUVA-1; Mon, 23 Jan 2023 07:00:49 -0500 X-MC-Unique: UdwdbkYsMe6BQydYc7CUVA-1 Received: from smtp.corp.redhat.com (int-mx10.intmail.prod.int.rdu2.redhat.com [10.11.54.10]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 7E6BB802BEE; Mon, 23 Jan 2023 12:00:48 +0000 (UTC) Received: from warthog.procyon.org.uk (unknown [10.33.36.23]) by smtp.corp.redhat.com (Postfix) with ESMTP id D0C3C492B02; Mon, 23 Jan 2023 12:00:46 +0000 (UTC) Organization: Red Hat UK Ltd. 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Registered in England and Wales under Company Registration No. 3798903 From: David Howells In-Reply-To: <3814749.1674474663@warthog.procyon.org.uk> References: <3814749.1674474663@warthog.procyon.org.uk> <246ba813-698b-8696-7f4d-400034a3380b@redhat.com> <20230120175556.3556978-1-dhowells@redhat.com> <20230120175556.3556978-3-dhowells@redhat.com> Cc: dhowells@redhat.com, David Hildenbrand , Al Viro , Christoph Hellwig , Matthew Wilcox , Jens Axboe , Jan Kara , Jeff Layton , Logan Gunthorpe , linux-fsdevel@vger.kernel.org, linux-block@vger.kernel.org, linux-kernel@vger.kernel.org, Christoph Hellwig , John Hubbard , linux-mm@kvack.org Subject: Re: [PATCH v7 2/8] iov_iter: Add a function to extract a page list from an iterator MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-ID: <3815848.1674475246.1@warthog.procyon.org.uk> Content-Transfer-Encoding: quoted-printable Date: Mon, 23 Jan 2023 12:00:46 +0000 Message-ID: <3815849.1674475246@warthog.procyon.org.uk> X-Scanned-By: MIMEDefang 3.1 on 10.11.54.10 X-Rspamd-Server: rspam07 X-Rspamd-Queue-Id: 2353B80022 X-Rspam-User: X-Stat-Signature: 6ocyof89hsex8dm74ki9an5r396s6csc X-HE-Tag: 1674475255-428876 X-HE-Meta: U2FsdGVkX18hbnPRo9YS/nbrmwEQTI2ZdLlcNlmih67r7pPfiYdUk9BlBsmxw3sWBb5Gnuv8PGMWFlbWZuoup5TzZmFadwtocSvly1xK+bQSCLJ27gQxiRNFx+elG+JoPU8+zlKn/ynPetoHgjRvww/F3ijYqh9l+xB/674owSF6tTiMmHzI8t1PZzuPau6Lv3hjTBZTBoNYnxwFUPLDMEfLookk88tvSHy7ivLvzpD40ffqtikqUZJCCdY8f0p99Ph1qVHc+alG1+TNB4hj/lsJy7MAYjp/P+lY97cFjI4dqXN+NSdeSs/D7N8byC+C4VPpkvvqeCW53yP0L1XiohEnomizFaHRCrUPAYSdSJKc1Z4uhm7GMDC9oSY024UWkmePlj4768izkvi6UIkk8dGqDFae6hzjiipuEhD+jmmiN27mjykzxRarzrgIeMD2pJHj3h/QOgTTWerewclQCx5FIsKnCGjYmSCyQLPpUF2vxGK+z2z5vwl4Tt6t7RWzczTmGkM4Dav4i1ezAZfmJt4H+TZNlvlrBz5rPQooflp296h9FX7gwiDsL0p2IGKKFaYCv35TZK4QZ94f18VvcR9BeYoGIDLmn5XAvUb8fwt+Um6zxw8cgM13i80c5rfwIcsZ7lsJGoq32fuR99lm/1cHh8oo6CjTbiVE6l1vW1wisRGY2C5eTHlCskYKAGBg3J6gogl83Fwwe/DKEXMuAy5t19uR4BzX3jSj5yd81O0RzDq0JHaUHSW6PdPGk5g/n3rUeLuxUWd9zn1Yh1n3M57sRFeCn/mMpN/ywMqyYCqtbTUvZIeM+5rKtXtOtnEVy+qB83wL1eGiRGawT6HwJr5DVwxOXZActjg3XewrOLV2wZCCERA5+xK7v4PLSyivi2vjl8pKaSgP/2OqS14TyjNj3gSCMAPUucnmX1BPZ01NQM4joGMC4k2gqoTaHLyHOsEjJqUDHMFap+H2U79 YAAnjrC3 OCCDDTzP0gdyHyyNnAD6fmWUMgaZUvOMese9TggGuLAvfXhlwcf1u+aOkyPIOyzhwegBbDf5efRcsqGrzK3xCYYXcv8X/bzQyvgRP2y6+YamieDWMo502FyXwYtrmHVAlj8f76mQISQSDmC5S77wXoMpkLXttFSUSFgWp2FzYCNh6YAgLkv96Gwncbq5wPoAKt7DTlm7oySZi9wn9AQoPHviacVsSxR5Rv7PKR/R8PVXramIX9UZg0zuHjf//z29Zw436YtO/oa7GGf4blZkUuBAx36NszsOkmLhNx7W08XyuO2Hf5deUYcubuii237o0FPWYI5DrKZ43oMhNKHTl/a8htu1D2xErJ7yScw0T+NhRJyo= 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: David Howells wrote: > > How does this work align with the goal of no longer using FOLL_GET for > > O_DIRECT? We should get rid of any FOLL_GET usage for accessing page c= ontent. > = > Would that run the risk of changes being made by the child being visible= to > the a DIO write if the parent changes the buffer first? > = > = > PARENT CHILD > =3D=3D=3D=3D=3D=3D =3D=3D=3D=3D=3D > start-DIO-write > fork() =3D pid fork() =3D 0 > alter-buffer > CoW happens > page copied original page retained > alter-buffer > Ah, I think I might have got the wrong end of the stick. A pinned page is *always* copied on fork() if I understand copy_present_pte() correctly. David