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=-7.3 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 142BDC5519F for ; Fri, 27 Nov 2020 17:00:59 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 944A420809 for ; Fri, 27 Nov 2020 17:00:58 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="ApWSWI89" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 944A420809 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id E7C186B0072; Fri, 27 Nov 2020 12:00:57 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id E51BD6B0074; Fri, 27 Nov 2020 12:00:57 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id CF1C56B0075; Fri, 27 Nov 2020 12:00:57 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0084.hostedemail.com [216.40.44.84]) by kanga.kvack.org (Postfix) with ESMTP id BA2076B0072 for ; Fri, 27 Nov 2020 12:00:57 -0500 (EST) Received: from smtpin08.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay04.hostedemail.com (Postfix) with ESMTP id 799962490 for ; Fri, 27 Nov 2020 17:00:57 +0000 (UTC) X-FDA: 77530812954.08.cart92_1b0474427389 Received: from filter.hostedemail.com (10.5.16.251.rfc1918.com [10.5.16.251]) by smtpin08.hostedemail.com (Postfix) with ESMTP id 41D6B1819E624 for ; Fri, 27 Nov 2020 17:00:57 +0000 (UTC) X-HE-Tag: cart92_1b0474427389 X-Filterd-Recvd-Size: 2970 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [63.128.21.124]) by imf12.hostedemail.com (Postfix) with ESMTP for ; Fri, 27 Nov 2020 17:00:56 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1606496456; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to: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=EhEV+wsKeWCLvw5Za69I3r2D9GX7zL+Z/rQpU2ehWsk=; b=ApWSWI89nScv/PCt/2S1juP1C5B2nL0FZJnqui/dAc/NlgwxkjoRMI56VyGTLn1MicUhCI Z9M5WkBV3x324SOBQJm3bAa6X3ORsKk2bCOKOy2mWpcHIOKns6L3U2+CE+TSxiiR/7pxud fokyJVF7mfE5A+stk5XJRwzanCSRomk= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-492-Dfa3FLZZOq6u9dtbDTGfLQ-1; Fri, 27 Nov 2020 12:00:51 -0500 X-MC-Unique: Dfa3FLZZOq6u9dtbDTGfLQ-1 Received: from smtp.corp.redhat.com (int-mx01.intmail.prod.int.phx2.redhat.com [10.5.11.11]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 75A9A8145E5; Fri, 27 Nov 2020 17:00:49 +0000 (UTC) Received: from [10.36.114.118] (ovpn-114-118.ams2.redhat.com [10.36.114.118]) by smtp.corp.redhat.com (Postfix) with ESMTP id 1E5605B4A0; Fri, 27 Nov 2020 17:00:44 +0000 (UTC) Subject: Re: [PATCH] mm: Don't fault around userfaultfd-registered regions on reads To: Peter Xu , linux-kernel@vger.kernel.org, linux-mm@kvack.org Cc: Andrew Morton , Hugh Dickins , Andrea Arcangeli , Mike Rapoport References: <20201126222359.8120-1-peterx@redhat.com> From: David Hildenbrand Organization: Red Hat GmbH Message-ID: Date: Fri, 27 Nov 2020 18:00:44 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.4.0 MIME-Version: 1.0 In-Reply-To: <20201126222359.8120-1-peterx@redhat.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit X-Scanned-By: MIMEDefang 2.79 on 10.5.11.11 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 26.11.20 23:23, Peter Xu wrote: > Faulting around for reads are in most cases helpful for the performance so that > continuous memory accesses may avoid another trip of page fault. However it > may not always work as expected. > > For example, userfaultfd registered regions may not be the best candidate for > pre-faults around the reads. Are we getting uffd faults even though no-one actually accessed it? So in case I would track what some part of my program actually reads, I would get wrong notifications? -- Thanks, David / dhildenb