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=-2.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,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 C5748C4321A for ; Fri, 28 Jun 2019 10:05:59 +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 A06D6208CB for ; Fri, 28 Jun 2019 10:05:59 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org A06D6208CB 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]:58432 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.86_2) (envelope-from ) id 1hgnlW-00065C-UQ for qemu-devel@archiver.kernel.org; Fri, 28 Jun 2019 06:05:58 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:53693) by lists.gnu.org with esmtp (Exim 4.86_2) (envelope-from ) id 1hgnki-00051h-28 for qemu-devel@nongnu.org; Fri, 28 Jun 2019 06:05:16 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1hgnkd-0007Az-3u for qemu-devel@nongnu.org; Fri, 28 Jun 2019 06:05:07 -0400 Received: from mx1.redhat.com ([209.132.183.28]:42528) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1hgnkC-0006XB-GW; Fri, 28 Jun 2019 06:04:39 -0400 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 mx1.redhat.com (Postfix) with ESMTPS id 834733DD47; Fri, 28 Jun 2019 10:04:26 +0000 (UTC) Received: from dhcp-200-226.str.redhat.com (dhcp-200-226.str.redhat.com [10.33.200.226]) by smtp.corp.redhat.com (Postfix) with ESMTPS id BE79B1A92E; Fri, 28 Jun 2019 10:04:23 +0000 (UTC) Date: Fri, 28 Jun 2019 12:04:22 +0200 From: Kevin Wolf To: Alberto Garcia Message-ID: <20190628100422.GE5179@dhcp-200-226.str.redhat.com> References: <20190627135914.xlzohrdwr6mz2aq3@perseus.local> <4453cfc4-cff7-c004-1f4c-7cab462e4661@virtuozzo.com> <20190628092057.GA5179@dhcp-200-226.str.redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.11.3 (2019-02-01) X-Scanned-By: MIMEDefang 2.84 on 10.5.11.23 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.29]); Fri, 28 Jun 2019 10:04:26 +0000 (UTC) X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] X-Received-From: 209.132.183.28 Subject: Re: [Qemu-devel] [RFC] Re-evaluating subcluster allocation for qcow2 images 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: Anton Nefedov , Denis Lunev , "qemu-block@nongnu.org" , "qemu-devel@nongnu.org" , Max Reitz Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" Am 28.06.2019 um 11:53 hat Alberto Garcia geschrieben: > On Fri 28 Jun 2019 11:20:57 AM CEST, Kevin Wolf wrote: > >> >> I would consider 64k cluster/8k subcluster as too extreme for me. > >> > >> I forgot to add: this 64k/8k ratio is only with my current prototype. > >> > >> In practice if we go with the 128-bit L2 entries we would have 64 > >> subclusters per cluster, or 32 if we want to have a separate > >> QCOW_OFLAG_ZERO for each subcluster (would we need this?). > > > > Yes, I think we'd want to have a separate zero flag for each > > subcluster. Otherwise, when writing to a zero cluster, you'd have to > > COW the whole supercluster again. > > Yes if the original cluster had the QCOW_OFLAG_ZERO bit, not if it was > simply unallocated. Right, but that leaving clusters simply unallocated doesn't quite cut it is something we already noticed before writing the spec for v3. Only really necessary when you have a backing file, of course, but that's one of the more interesting cases for subclusters anyway. Kevin