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=-2.7 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, 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 725DAC2B9F4 for ; Tue, 22 Jun 2021 18:16:13 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 557A961289 for ; Tue, 22 Jun 2021 18:16:13 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232386AbhFVSS1 (ORCPT ); Tue, 22 Jun 2021 14:18:27 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:41778 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229612AbhFVSSX (ORCPT ); Tue, 22 Jun 2021 14:18:23 -0400 Received: from mail-pg1-x529.google.com (mail-pg1-x529.google.com [IPv6:2607:f8b0:4864:20::529]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id C687FC061574; Tue, 22 Jun 2021 11:16:07 -0700 (PDT) Received: by mail-pg1-x529.google.com with SMTP id t9so17772572pgn.4; Tue, 22 Jun 2021 11:16:07 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=mime-version:subject:from:in-reply-to:date:cc :content-transfer-encoding:message-id:references:to; bh=LvlqUd76IAy9L7kdhodL+NG05Os6O0cVnFr95gFkQvM=; b=NFhodhGHGGFBpXeVNZ3VtVimQGMgS4j13UL3omISPfnTJdZmAAcssg5FkMCjZJ6GtY 2emg4vs+l1ZiKR6HrdAPmh6nIInlpAwJcOk4dWMvavgDZVfpF03nRY9QGNnXnz7XklF8 wLYXVBBk8Cyqp/xoszIZxZ4xPs66gNVNIE0nVoTHZoouQE214nqTxGrkCDceq/XhfXo8 3W91ZZsHxpiT5BdwB/v+veZaU5UYn1HnkhbStmXbLibp62yBmPLQWQDvn45V6suoPnTQ 3wn2r9gaaqc33TMzVVqCMAiyqpyGjByUVsT9wtgTQHQrk0hsnuc/YsUIiwDLi1vcF3k3 Nvyw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:subject:from:in-reply-to:date:cc :content-transfer-encoding:message-id:references:to; bh=LvlqUd76IAy9L7kdhodL+NG05Os6O0cVnFr95gFkQvM=; b=msCfgefXFyZkaPYSGrnbR9580xbzw6UVJ2aK9LTpfPsii3SLN5lGBm1fGKC1WjHocf rn3eqvNE1YkGiJ8LLw7U4EMDI6rLWNnbJBV6LFfWlMvNAaee1w2wvpQ6kJWCb6UxQprJ GBPtAM0y/Cg+TXEAtnAo/qcsl89NpQtHRFu/WdqzGuhyW+YcOlUIAzUCIu7wIxhDqlXy dgPB2mWwBso/5zwWReVoQ141B4sJSQlwJ3L2eiBZ8nhliFV+xkinHbu4CyQ9qSZPkgJx gnnBKAcw8rRkYsaapD0eEugK0sdqEHPF9MzrdzvqfsqV/ZzlrigltgZmKuowapMpLENx MKrA== X-Gm-Message-State: AOAM531aA4tfcuzjyOzMyUyHn6vKQL5+HDAYfYYE8cLXou7Hwzc4RkvC +Z9HIqIPwJ7w9zJWelN/zw43N3tbTMSW1Q== X-Google-Smtp-Source: ABdhPJycAUB8Y1J8RSIc/cFA/fer7B+da2ICW/wH5DbTzVV8vS8ArfYM8UTJ8N9qR49CebfnJIr6XQ== X-Received: by 2002:a65:5ac9:: with SMTP id d9mr5042005pgt.293.1624385767083; Tue, 22 Jun 2021 11:16:07 -0700 (PDT) Received: from smtpclient.apple (c-24-6-216-183.hsd1.ca.comcast.net. [24.6.216.183]) by smtp.gmail.com with ESMTPSA id c3sm42759pfl.42.2021.06.22.11.16.05 (version=TLS1_2 cipher=ECDHE-ECDSA-AES128-GCM-SHA256 bits=128/128); Tue, 22 Jun 2021 11:16:06 -0700 (PDT) Content-Type: text/plain; charset=utf-8 Mime-Version: 1.0 (Mac OS X Mail 14.0 \(3654.100.0.2.22\)) Subject: Re: Do we need to unrevert "fs: do not prefault sys_write() user buffer pages"? From: Nadav Amit In-Reply-To: Date: Tue, 22 Jun 2021 11:16:03 -0700 Cc: Matthew Wilcox , David Howells , Al Viro , Ted Ts'o , Dave Hansen , Andrew Morton , Linux-MM , Ext4 Developers List , linux-fsdevel , Linux Kernel Mailing List Content-Transfer-Encoding: quoted-printable Message-Id: <437C30AA-2256-4F4F-9CC0-363A21DB1044@gmail.com> References: <3221175.1624375240@warthog.procyon.org.uk> <3231150.1624384533@warthog.procyon.org.uk> To: Linus Torvalds X-Mailer: Apple Mail (2.3654.100.0.2.22) Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org > On Jun 22, 2021, at 11:07 AM, Linus Torvalds = wrote: >=20 > On Tue, Jun 22, 2021 at 11:05 AM Matthew Wilcox = wrote: >>=20 >> Huh? Last I checked, the fault_in_readable actually read a byte from >> the page. It has to wait for the read to complete before that can >> happen. >=20 > Yeah, we don't have any kind of async fault-in model. >=20 > I'm not sure how that would even look. I don't think it would > necessarily be *impossible* (special marker in the exception table to > let the fault code know that this is a "prepare" fault), but it would > be pretty challenging. I did send an RFC some time ago for =E2=80=9Cprepare=E2=80=9D fault, but = it the RFC requires some more work. https://lore.kernel.org/lkml/20210225072910.2811795-1-namit@vmware.com/