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=-5.3 required=3.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED,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 B4BE9C433E0 for ; Tue, 9 Feb 2021 12:41:31 +0000 (UTC) Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 0A18464E60 for ; Tue, 9 Feb 2021 12:41:30 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 0A18464E60 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Received: from localhost ([::1]:50132 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1l9SKf-00062Y-QF for qemu-devel@archiver.kernel.org; Tue, 09 Feb 2021 07:41:29 -0500 Received: from eggs.gnu.org ([2001:470:142:3::10]:52732) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1l9SGz-0004pQ-JY for qemu-devel@nongnu.org; Tue, 09 Feb 2021 07:37:41 -0500 Received: from us-smtp-delivery-124.mimecast.com ([216.205.24.124]:46267) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_CBC_SHA1:256) (Exim 4.90_1) (envelope-from ) id 1l9SGw-00079x-Ps for qemu-devel@nongnu.org; Tue, 09 Feb 2021 07:37:41 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1612874256; 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=4rvgdZDX9w6qfsZu3s/3KgUMPaEuxvIbUpK2Qc7kiKM=; b=UQGukW9efRQEIci+pLgp1+uOUI+PBzs0nmf3d1pjJS6pJAETTDR2o8te1/7slgYjT1aJQr z1vR6A+YC4NbFot2FIGcLD1rV+NPZgujki/R0+jDnPaD8Xbbzzg0vKAeZ8MF0p0YRSBKcF 0vEg8gL1gtAdqeWsSWPY1+dAEgzxiaE= 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-281-IrYPNdrYPiG3i3OTPjDxfA-1; Tue, 09 Feb 2021 07:37:33 -0500 X-MC-Unique: IrYPNdrYPiG3i3OTPjDxfA-1 Received: from smtp.corp.redhat.com (int-mx05.intmail.prod.int.phx2.redhat.com [10.5.11.15]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 67C74192CC41; Tue, 9 Feb 2021 12:37:32 +0000 (UTC) Received: from [10.36.113.141] (ovpn-113-141.ams2.redhat.com [10.36.113.141]) by smtp.corp.redhat.com (Postfix) with ESMTP id BE9605D6D7; Tue, 9 Feb 2021 12:37:27 +0000 (UTC) To: Andrey Gruzdev , qemu-devel@nongnu.org References: <20210121152458.193248-1-andrey.gruzdev@virtuozzo.com> From: David Hildenbrand Organization: Red Hat GmbH Subject: Re: [PATCH v13 0/5] UFFD write-tracking migration/snapshots Message-ID: Date: Tue, 9 Feb 2021 13:37:26 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.5.0 MIME-Version: 1.0 In-Reply-To: <20210121152458.193248-1-andrey.gruzdev@virtuozzo.com> X-Scanned-By: MIMEDefang 2.79 on 10.5.11.15 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=david@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 8bit Received-SPF: pass client-ip=216.205.24.124; envelope-from=david@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -35 X-Spam_score: -3.6 X-Spam_bar: --- X-Spam_report: (-3.6 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.57, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, NICE_REPLY_A=-0.265, RCVD_IN_DNSWL_LOW=-0.7, RCVD_IN_MSPIKE_H3=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Juan Quintela , Markus Armbruster , Peter Xu , "Dr . David Alan Gilbert" , Paolo Bonzini , Den Lunev Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 21.01.21 16:24, andrey.gruzdev--- via wrote: > This patch series is a kind of 'rethinking' of Denis Plotnikov's ideas he's > implemented in his series '[PATCH v0 0/4] migration: add background snapshot'. > > Currently the only way to make (external) live VM snapshot is using existing > dirty page logging migration mechanism. The main problem is that it tends to > produce a lot of page duplicates while running VM goes on updating already > saved pages. That leads to the fact that vmstate image size is commonly several > times bigger then non-zero part of virtual machine's RSS. Time required to > converge RAM migration and the size of snapshot image severely depend on the > guest memory write rate, sometimes resulting in unacceptably long snapshot > creation time and huge image size. > > This series propose a way to solve the aforementioned problems. This is done > by using different RAM migration mechanism based on UFFD write protection > management introduced in v5.7 kernel. The migration strategy is to 'freeze' > guest RAM content using write-protection and iteratively release protection > for memory ranges that have already been saved to the migration stream. > At the same time we read in pending UFFD write fault events and save those > pages out-of-order with higher priority. > Hi, just stumbled over this, quick question: I recently played with UFFD_WP and notices that write protection is only effective on pages/ranges that have already pages populated (IOW: !pte_none() in the kernel). In case memory was never populated (or was discarded using e.g., madvice(DONTNEED)), write-protection will be skipped silently and you won't get WP events for applicable pages. So if someone writes to a yet unpoupulated page ("zero"), you won't get WP events. I can spot that you do a single uffd_change_protection() on the whole RAMBlock. How are you handling that scenario, or why don't you have to handle that scenario? -- Thanks, David / dhildenb