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=-15.1 required=3.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=ham 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 CAA70C433C1 for ; Fri, 19 Mar 2021 16:43:26 +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 2F69E61981 for ; Fri, 19 Mar 2021 16:43:26 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 2F69E61981 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]:40090 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1lNIDd-0007Qs-Ae for qemu-devel@archiver.kernel.org; Fri, 19 Mar 2021 12:43:25 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:54296) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1lNIBV-0006Kq-HE for qemu-devel@nongnu.org; Fri, 19 Mar 2021 12:41:13 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]:33827) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1lNIBS-0008Ve-71 for qemu-devel@nongnu.org; Fri, 19 Mar 2021 12:41:12 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1616172068; 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=/J21uGETHrwDAQyywr78OoqTBzmfq1JJzK21QIoQzG0=; b=awfqUL0E7f4jS2Ub6AwmVAW2N/3KCYeA3AXSrdBfKJpXnF1mecwfSEHtERiYry6U1P8cLC aTNMUY2Mly96JnwT8+DJ3cGh86j7AjfcP5CSp9XI21iIT/PVxtTgo1ifTrkm0oLbogDqQs r05cd8kk/HeG9e5XPNxir5QzCIjTqF0= 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-244-COPPw1gYM6OcsCEWKDXr9A-1; Fri, 19 Mar 2021 12:41:07 -0400 X-MC-Unique: COPPw1gYM6OcsCEWKDXr9A-1 Received: from smtp.corp.redhat.com (int-mx02.intmail.prod.int.phx2.redhat.com [10.5.11.12]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id DD94B107ACCA; Fri, 19 Mar 2021 16:41:05 +0000 (UTC) Received: from [10.36.112.130] (ovpn-112-130.ams2.redhat.com [10.36.112.130]) by smtp.corp.redhat.com (Postfix) with ESMTP id 0994160BF1; Fri, 19 Mar 2021 16:40:52 +0000 (UTC) Subject: Re: [PATCH v4 13/14] qmp: Include "reserve" property of memory backends To: Markus Armbruster References: <20210319101230.21531-1-david@redhat.com> <20210319101230.21531-14-david@redhat.com> <87ft0ri23r.fsf@dusky.pond.sub.org> <84f961a5-6292-8364-9491-f8330b401a65@redhat.com> <87zgyzf6jq.fsf@dusky.pond.sub.org> From: David Hildenbrand Organization: Red Hat GmbH Message-ID: <9763d3e3-3313-ac5c-035e-89175f2460a2@redhat.com> Date: Fri, 19 Mar 2021 17:40:52 +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: <87zgyzf6jq.fsf@dusky.pond.sub.org> X-Scanned-By: MIMEDefang 2.79 on 10.5.11.12 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: -29 X-Spam_score: -3.0 X-Spam_bar: --- X-Spam_report: (-3.0 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.251, 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: Marcel Apfelbaum , Eduardo Habkost , "Michael S. Tsirkin" , Igor Kotrasinski , Richard Henderson , qemu-devel@nongnu.org, Peter Xu , "Dr. David Alan Gilbert" , Greg Kurz , Stefan Hajnoczi , Murilo Opsfelder Araujo , Paolo Bonzini , =?UTF-8?Q?Philippe_Mathieu-Daud=c3=a9?= , Igor Mammedov Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 19.03.21 17:32, Markus Armbruster wrote: > David Hildenbrand writes: > >> On 19.03.21 16:40, Markus Armbruster wrote: >>> David Hildenbrand writes: >>> >>>> Let's include the new property. >>>> >>>> Cc: Eric Blake >>>> Cc: Markus Armbruster >>>> Signed-off-by: David Hildenbrand >>>> --- >>>> hw/core/machine-qmp-cmds.c | 1 + >>>> qapi/machine.json | 6 ++++++ >>>> 2 files changed, 7 insertions(+) >>>> >>>> diff --git a/hw/core/machine-qmp-cmds.c b/hw/core/machine-qmp-cmds.c >>>> index 68a942595a..bd2a7f2dd0 100644 >>>> --- a/hw/core/machine-qmp-cmds.c >>>> +++ b/hw/core/machine-qmp-cmds.c >>>> @@ -174,6 +174,7 @@ static int query_memdev(Object *obj, void *opaque) >>>> m->merge = object_property_get_bool(obj, "merge", &error_abort); >>>> m->dump = object_property_get_bool(obj, "dump", &error_abort); >>>> m->prealloc = object_property_get_bool(obj, "prealloc", &error_abort); >>>> + m->reserve = object_property_get_bool(obj, "reserve", &error_abort); >>>> m->policy = object_property_get_enum(obj, "policy", "HostMemPolicy", >>>> &error_abort); >>>> host_nodes = object_property_get_qobject(obj, >>>> diff --git a/qapi/machine.json b/qapi/machine.json >>>> index c0c52aef10..12860a1f79 100644 >>>> --- a/qapi/machine.json >>>> +++ b/qapi/machine.json >>>> @@ -814,6 +814,11 @@ >>>> # >>>> # @prealloc: enables or disables memory preallocation >>>> # >>>> +# @reserve: enables or disables reservation of swap space (or huge pages >>>> +# if applicable). If reservation is enabled (default), actual >>>> +# reservation depends on underlying OS support. In contrast, >>>> +# disabling reservation without OS support will bail out. (since 6.1) >>>> +# >>> >>> Provides two settings: "enable reservation if possible", and "disable >>> reservation or else fail". >>> >>> Does "enable reservation or else fail" make no sense, or is it merely >>> unimplemented? >> >> The default for now used to be "enable reservation if possible". For >> example, Windows always reserves/commits the whole region. Under >> Linux, reservation is always done for private memory mappings, >> however, especially for basically all (with one exception) shared >> memory there is no reservation of any kind (with another exception). >> >> For example, it does not make sense to reserve swap space for a >> file-backed mapping; we can just writeback to the file in case we run >> out of memory. Therefore, Linux will never reserve swap space in that case. >> >> So if we were to implement a "enable reservation or else fail", the >> default ("true") would no longer work for existing setups. >> >> Usually we want "enable reservation if possible" unless in spacial >> cases ("definitely avoid the reservation") > > Wait a second... struct Memdev is actually the result of query-memdev, > and *not* a command or option argument. > > Saying "enables or disables reservation of swap space" is misleading. > This isn't ever about enabling or disabling things, it's about querying > whether things are enabled or disabled. > > Existing member documentation has the same issue: > > # @merge: enables or disables memory merge support > # > # @dump: includes memory backend's memory in a core dump or not > # > # @prealloc: enables or disables memory preallocation Yes, I was only playing along although it looked kind of weird ... > > Should be something like > > # @merge: whether memory merge support is enabled > # > # @dump: whether the memory backend's memory is included in a core dump > # > # @prealloc: whether memory is preallocated > I'll include a cleanup for these in the next version. > The new member could be phrased like: > > # @reserved: whether swap space (or huge pages if applicable) have > # been reserved. > > Mind, I'm proposing how to phrase things, not how things are. You'll > likely have to adjust the contents of my proposal to match reality. > > If we can't always tell whether swap space (or whatever) has been > reserved, then > > * If we can only ever tell when it has *not* been reserved, make false > mean "not reserved", and true mean "dunno". > > * If we can tell sometimes > > - but nobody cares for the difference between "reserved" and "dunno", > same as above. > > - and users may care for the difference, we need three values: "not > reserved", "reserved", and "dunno". There are various ways to do > that. No use talking about them before we know we need one of them. Right, usually we care about "reserve is a reservation makes sense and is possible" - decided by the OS and "definitely don't reserve if you would have reserved anything". Thanks! -- Thanks, David / dhildenb