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=-5.1 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 8DEE6C433DB for ; Tue, 2 Mar 2021 13:18:01 +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 129C160231 for ; Tue, 2 Mar 2021 13:18:01 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 129C160231 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]:50320 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1lH4uW-0005uV-3o for qemu-devel@archiver.kernel.org; Tue, 02 Mar 2021 08:18:00 -0500 Received: from eggs.gnu.org ([2001:470:142:3::10]:44212) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1lH4s6-0004pT-H2 for qemu-devel@nongnu.org; Tue, 02 Mar 2021 08:15:30 -0500 Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]:41784) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_CBC_SHA1:256) (Exim 4.90_1) (envelope-from ) id 1lH4s3-0008KK-SP for qemu-devel@nongnu.org; Tue, 02 Mar 2021 08:15:30 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1614690925; 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=pm0JwZT9/IKvBzp25Ye5fXmfWOuYg/xbiV+nPc74RkA=; b=OO3Hek9SAViuoHRMMXPe95qSdafp9Y2yOFlVzLn+zQrdTtTnVU2p7VfHWlAefHo6E1aZHx lgx7VzOVK3D40glwl4bqvmjG80c74UJ40jq5m8mQ6M688Ee2VqG3xByLPuvOVlajPq7nll kk3LezAdXXs/SfuxZYhwug6na3SvMsg= 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-44-qW7eSrd5NaG5YD_uTScIEw-1; Tue, 02 Mar 2021 08:13:07 -0500 X-MC-Unique: qW7eSrd5NaG5YD_uTScIEw-1 Received: from smtp.corp.redhat.com (int-mx08.intmail.prod.int.phx2.redhat.com [10.5.11.23]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id C4E2C1E562; Tue, 2 Mar 2021 13:13:05 +0000 (UTC) Received: from [10.36.114.189] (ovpn-114-189.ams2.redhat.com [10.36.114.189]) by smtp.corp.redhat.com (Postfix) with ESMTP id BDDFF1A863; Tue, 2 Mar 2021 13:12:52 +0000 (UTC) Subject: Re: [PATCH v1 0/9] RAM_NORESERVE, MAP_NORESERVE and hostmem "reserve" property To: qemu-devel@nongnu.org References: <20210209134939.13083-1-david@redhat.com> From: David Hildenbrand Organization: Red Hat GmbH Message-ID: Date: Tue, 2 Mar 2021 14:12:51 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.8.0 MIME-Version: 1.0 In-Reply-To: <20210209134939.13083-1-david@redhat.com> X-Scanned-By: MIMEDefang 2.84 on 10.5.11.23 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: 7bit Received-SPF: pass client-ip=170.10.133.124; envelope-from=david@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -27 X-Spam_score: -2.8 X-Spam_bar: -- X-Spam_report: (-2.8 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.001, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, NICE_REPLY_A=-0.001, RCVD_IN_DNSWL_LOW=-0.7, RCVD_IN_MSPIKE_H4=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 , Thomas Huth , Cornelia Huck , Eduardo Habkost , "Michael S. Tsirkin" , Stefan Weil , Murilo Opsfelder Araujo , Richard Henderson , "Dr. David Alan Gilbert" , Peter Xu , Greg Kurz , Halil Pasic , Christian Borntraeger , Stefan Hajnoczi , Igor Mammedov , Paolo Bonzini , =?UTF-8?Q?Philippe_Mathieu-Daud=c3=a9?= , Igor Kotrasinski Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 09.02.21 14:49, David Hildenbrand wrote: > Some cleanups previously sent in other context (resizeable allocations), > followed by RAM_NORESERVE, implementing it under POSIX using MAP_NORESERVE, > and letting users configure it for memory backens using the "reserve" > property (default: true). > > MAP_NORESERVE under Linux has in the context of QEMU an effect on > 1) Private anonymous memory > -> memory-backend-ram,id=mem0,size=10G > 2) Private file-based mappings > -> memory-backend-file,id=mem0,size=10G,mem-path=/dev/shm/0 > 3) Private/shared hugetlbfs memory > -> memory-backend-memfd,id=mem0,size=10G,hugetlb=on,hugetlbsize=2M > > With MAP_NORESERVE/"reserve=off", we won't be reserving swap space (1/2) or > huge pages (3) for the whole memory region. > > The target use case is virtio-mem, which dynamically exposes memory > inside a large, sparse memory area to the VM. MAP_NORESERVE tells the OS > "this mapping might be very sparse". This essentially allows > avoiding to set "/proc/sys/vm/overcommit_memory == 0") when using > virtio-mem and also supporting hugetlbfs in the future. > > virtio-mem currently only supports anonymous memory, in the future we want > to also support shared file-based and shared hugetlbfs mappings. We most > probably won't be supporting private mappings as they can end up behaving > very weird when it comes to memory consumption. > > Future work for virtio-mem I am currently working on includes > 1. Introducing a prealloc option for virtio-mem (e.g., using fallocate() > when plugging blocks) to fail nicely when running out of > backing storage like huge pages. > 2. Supporting resizable RAM block/memoryr egions, such that we won't always > expose a large, sparse memory region to the VM. > 3. Protecting unplugged memory e.g., using userfaultfd. > 4. (resizeable allocations / optimized mmap handling when resizing RAM > blocks) Ping -- Thanks, David / dhildenb