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 lists1p.gnu.org (lists1p.gnu.org [209.51.188.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id D51E3FA1FC5 for ; Wed, 22 Apr 2026 16:31:05 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists1p.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1wFaT9-00057v-UX; Wed, 22 Apr 2026 12:30:31 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]) by lists1p.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1wFaT5-00057I-Fl for qemu-devel@nongnu.org; Wed, 22 Apr 2026 12:30:30 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1wFaT3-0003Kx-Sh for qemu-devel@nongnu.org; Wed, 22 Apr 2026 12:30:27 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1776875422; 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=BjmfO0yef6kA1xNy1Y3HMovxD+y48D5FJPyYtPucIfg=; b=WAESOtahv7B+r3BOxBN/inR3QdT1ZJZ5w2ltmXYbWmMEXSecRCPJsSyv0pxola+nd/fSOH Tc9wPNcLH45v2VaYUTWKeAdEp11tq3VSvB3EHdL5eobF5PdzKhnm3cMT5x9/+8ToZ89rmn /1cq31CTEU44Yat2VxqWeGVa4TMMESw= Received: from mx-prod-mc-01.mail-002.prod.us-west-2.aws.redhat.com (ec2-54-186-198-63.us-west-2.compute.amazonaws.com [54.186.198.63]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-220-qIeuUwPcM7GshO1j2F47Cg-1; Wed, 22 Apr 2026 12:30:19 -0400 X-MC-Unique: qIeuUwPcM7GshO1j2F47Cg-1 X-Mimecast-MFC-AGG-ID: qIeuUwPcM7GshO1j2F47Cg_1776875418 Received: from mx-prod-int-08.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-08.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.111]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by mx-prod-mc-01.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id EE07319560B3; Wed, 22 Apr 2026 16:30:17 +0000 (UTC) Received: from tpad.localdomain (unknown [10.96.133.3]) by mx-prod-int-08.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 801A9180045E; Wed, 22 Apr 2026 16:30:17 +0000 (UTC) Received: by tpad.localdomain (Postfix, from userid 1000) id 35F92400DFC8C; Mon, 20 Apr 2026 12:01:02 -0300 (-03) Date: Mon, 20 Apr 2026 12:01:02 -0300 From: Marcelo Tosatti To: Florian Schmidt Cc: Paolo Bonzini , Zhao Liu , qemu-devel@nongnu.org Subject: Re: [RFC PATCH 2/2] Add HvExtCallGetBootZeroedMemory Message-ID: References: <20260112113139.3762156-1-flosch@nutanix.com> <20260112113139.3762156-3-flosch@nutanix.com> <80e6ecc4-eac6-40ee-aaf8-da60daaf96d4@nutanix.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <80e6ecc4-eac6-40ee-aaf8-da60daaf96d4@nutanix.com> X-Scanned-By: MIMEDefang 3.4.1 on 10.30.177.111 Received-SPF: pass client-ip=170.10.133.124; envelope-from=mtosatti@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 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, RCVD_IN_DNSWL_NONE=-0.0001, SPF_HELO_PASS=-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: 2.1.29 Precedence: list List-Id: qemu development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org On Mon, Apr 20, 2026 at 10:25:43AM +0100, Florian Schmidt wrote: > Hi Marcelo, > > On 2026-04-17 06:51, Marcelo Tosatti wrote: > > Is this to improve boot time of very large guests ? > > It depends a bit on how you define "boot time". It won't make a difference > if you measure the time it takes to create the VM until you start the vCPUs. > It may even make a huge difference if you measure the time until a user can > first log in. > > What it will do is reduce the time the guest spends on writing memory, > mostly in the background, to zero out all pages it has gotten from the > hypervisor. The main advantage (other than saving CPU cycles that are > effectively wasted on an unneeded operation) is that if you don't > pre-allocate all the VMs memory, then the VM won't touch all pages after > boot, keeping the RSS down until the memory is actually used. That's for > example useful if you overcommit/oversubscribe VM memory. > > Cheers, > Florian Hi Florian, That is useful!