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 91FADC64EC4 for ; Wed, 8 Mar 2023 15:31:21 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 063D56B0072; Wed, 8 Mar 2023 10:31:21 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 013DF6B0074; Wed, 8 Mar 2023 10:31:20 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id DF61E6B0075; Wed, 8 Mar 2023 10:31:20 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0014.hostedemail.com [216.40.44.14]) by kanga.kvack.org (Postfix) with ESMTP id CFB186B0072 for ; Wed, 8 Mar 2023 10:31:20 -0500 (EST) Received: from smtpin12.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay09.hostedemail.com (Postfix) with ESMTP id 779B6810B3 for ; Wed, 8 Mar 2023 15:31:20 +0000 (UTC) X-FDA: 80546119920.12.B9E54DD Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) by imf06.hostedemail.com (Postfix) with ESMTP id 27E3B180021 for ; Wed, 8 Mar 2023 15:31:16 +0000 (UTC) Authentication-Results: imf06.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b="Y/33hyES"; spf=pass (imf06.hostedemail.com: domain of peterx@redhat.com designates 170.10.129.124 as permitted sender) smtp.mailfrom=peterx@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=1678289477; h=from:from:sender: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: in-reply-to:in-reply-to:references:references:dkim-signature; bh=eftDudG4vr7BCElathmFsHuVcD7xDHQqJ2O3beq4KM0=; b=HN71rz+a5TT80djoxxKbgV2o1mDP0+vWv9dDlU3rRMg49F2nNpwqRxnfT7oJP7ty+SfMqp X2eHfC6BCAnZQmdUAMtHGNjFB+62yq9rLThbqKCxe+0cxl47llzeWgQVkgj5TA2PB7WYET gYFz8qNdCUzZmWpP1onPMmzSzWCYp/I= ARC-Authentication-Results: i=1; imf06.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b="Y/33hyES"; spf=pass (imf06.hostedemail.com: domain of peterx@redhat.com designates 170.10.129.124 as permitted sender) smtp.mailfrom=peterx@redhat.com; dmarc=pass (policy=none) header.from=redhat.com ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1678289477; a=rsa-sha256; cv=none; b=1vJNN1GI0YjTHqjh1LC8dPN0+ncr8nEhKflOT1XA7SG2Qybc7hmTnuuqJRK6XDAc7DdU3y XzmeayLTeevI/nYR6hHyD8jpjYi5dBpr4YTpvVKe8rsdjZDjN+Gh8WNuFxd/7H+Kd0uxIt 7JVQCD1UopnFNRkrlnnQhBCS9lQ4E2E= DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1678289476; 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: in-reply-to:in-reply-to:references:references; bh=eftDudG4vr7BCElathmFsHuVcD7xDHQqJ2O3beq4KM0=; b=Y/33hyES0dXXoSn2cp6tGjwPpr79NwoXdY8eFfCr7ZUhIHtTGvAG1eCbcxZPcA/AZ/J5iL BesvxnY/Az8qtObeBpuGnmO8U1577CEH1WERf4SbOUY6PWzUu16IfpBn/qadU+GcrEFULs oOKTtWMU6nsJmU6VbE1evb2BpQzbl08= Received: from mail-qk1-f199.google.com (mail-qk1-f199.google.com [209.85.222.199]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-59-HOGNQBd0ODGFAOBipBoGmQ-1; Wed, 08 Mar 2023 10:31:12 -0500 X-MC-Unique: HOGNQBd0ODGFAOBipBoGmQ-1 Received: by mail-qk1-f199.google.com with SMTP id ou5-20020a05620a620500b007423e532628so9519682qkn.5 for ; Wed, 08 Mar 2023 07:31:12 -0800 (PST) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; t=1678289472; h=in-reply-to:content-disposition:mime-version:references:message-id :subject:cc:to:from:date:x-gm-message-state:from:to:cc:subject:date :message-id:reply-to; bh=eftDudG4vr7BCElathmFsHuVcD7xDHQqJ2O3beq4KM0=; b=D1O6N/PR10+ShcJ2ISChHc/vqDhXO41D5pc2mEhOmYivzPLlGTwBuVBHuadqP6Rfx8 hbGB1gVeJ7UliHOKXpN3/MeNs76tHhU/EBmR/XNuIhZaYuOEnwWbtpDPK2RWqelSkyjJ eM4S23T6sHb0QKDOC2qfuv7yB73/avTo3v4N/TLDo2+Kbnr9nJnLkvKj8LUPMwxDel9e 9naGTRoOgfcY2qJhzMiptRE7gRB4upYBEXj8JmVSvTTU5Ablcxyl2NwKzYHe6BPW4WAo bX22teKMTIveqaf/RbRb8pQ4Eu/mhtORuSL9m2iAKyKyqSddHCrqaqVpbKpZcy9bOjHk zmMg== X-Gm-Message-State: AO0yUKUug3QfXuRUcdMCgy6KVnOd03xUh3kHfLPlxkI2Dr6kmsSwAvZa BfjjWTtsFvSDAAcIwZ2nRyPmp0UjigxIt9yQSs2TaJDqsP2/7gp8cqgh/ZqWqOl+V7/nlVzENm8 6FD7o4UXrydE= X-Received: by 2002:a05:622a:8:b0:3bd:d8f:2da9 with SMTP id x8-20020a05622a000800b003bd0d8f2da9mr35990188qtw.2.1678289472264; Wed, 08 Mar 2023 07:31:12 -0800 (PST) X-Google-Smtp-Source: AK7set+hoTSuPiZP5GgpsCQn+QdWQJtKgt92kywG67pTawKqLEZWT+sEEEfsWjkysVAL3s0aiQhuEQ== X-Received: by 2002:a05:622a:8:b0:3bd:d8f:2da9 with SMTP id x8-20020a05622a000800b003bd0d8f2da9mr35990147qtw.2.1678289471932; Wed, 08 Mar 2023 07:31:11 -0800 (PST) Received: from x1n (bras-base-aurron9127w-grc-56-70-30-145-63.dsl.bell.ca. [70.30.145.63]) by smtp.gmail.com with ESMTPSA id i10-20020ac871ca000000b003bfb950f670sm11702664qtp.41.2023.03.08.07.31.10 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 08 Mar 2023 07:31:10 -0800 (PST) Date: Wed, 8 Mar 2023 10:31:09 -0500 From: Peter Xu To: David Hildenbrand Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, Muhammad Usama Anjum , Andrea Arcangeli , Axel Rasmussen , Mike Rapoport , Nadav Amit , Paul Gofman , Andrew Morton Subject: Re: [PATCH v3 1/2] mm/uffd: UFFD_FEATURE_WP_UNPOPULATED Message-ID: References: <20230306213925.617814-1-peterx@redhat.com> <20230306213925.617814-2-peterx@redhat.com> <94be7b9f-c33e-c6dc-4132-6cb78f7c0624@redhat.com> MIME-Version: 1.0 In-Reply-To: <94be7b9f-c33e-c6dc-4132-6cb78f7c0624@redhat.com> X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Disposition: inline X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: 27E3B180021 X-Stat-Signature: izpctbyu5iopqsfoun5akku6gmymduhc X-Rspam-User: X-HE-Tag: 1678289476-447059 X-HE-Meta: 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 keoqXfXv 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 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 Tue, Mar 07, 2023 at 05:11:07PM +0100, David Hildenbrand wrote: > On 06.03.23 22:39, Peter Xu wrote: > > Note that I wodnered for a second if we'd call it "UFFD_FEATURE_WP_MISSING" > instead (similar to the definition of MISSING uffd that triggers when we > have nothing mapped). I'll be fine with either WP_UNPOPULATED or WP_ZEROPAGE, but hope to avoid MISSING as that's definitely a keyword in uffd which can be confusing. > > Just a thought. > > [...] > > > With WP_UNPOPUATED, application like QEMU can avoid pre-read faults all the > > memory before wr-protect during taking a live snapshot. Quotting from > > Muhammad's test result here [3] based on a simple program [4]: > > > > (1) With huge page disabled > > echo madvise > /sys/kernel/mm/transparent_hugepage/enabled > > ./uffd_wp_perf > > Test DEFAULT: 4 > > Test PRE-READ: 1111453 (pre-fault 1101011) > > Test MADVISE: 278276 (pre-fault 266378) > > Test WP-UNPOPULATE: 11712 > > > > (2) With Huge page enabled > > echo always > /sys/kernel/mm/transparent_hugepage/enabled > > ./uffd_wp_perf > > Test DEFAULT: 4 > > Test PRE-READ: 22521 (pre-fault 22348) > > Test MADVISE: 4909 (pre-fault 4743) > > Test WP-UNPOPULATE: 14448 > > > > There'll be a great perf boost for no-thp case, while for thp enabled with > > extreme case of all-thp-zero WP_UNPOPULATED can be slower than MADVISE, but > > that's low possibility in reality, also the overhead was not reduced but > > postponed until a follow up write on any huge zero thp, so potentitially it > > s/potentitially/potentially/ > > > is faster by making the follow up writes slower. > > What I realized, interrestingly not only the writes, but also the reads. In Curious why reading a zeropage would be a problem? > case of background snapshots we'll be reading all VM memory I think ... but > we could optimize in QEMU by consulting the pagemap if there is anything > mapped at all, and not read zeros in that case [an optimization brought up > several times already]. > > I am not sure yet if we want to change the QEMU implementation. But anyhow, > that's a different discussion. The rest comments all look good here, I'll fix and resend, thanks. -- Peter Xu