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 77203C4321A for ; Fri, 28 Jun 2019 15:46:53 +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 4EC6A205C9 for ; Fri, 28 Jun 2019 15:46:53 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 4EC6A205C9 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]:33492 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.86_2) (envelope-from ) id 1hgt5Q-0006iA-9P for qemu-devel@archiver.kernel.org; Fri, 28 Jun 2019 11:46:52 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:53042) by lists.gnu.org with esmtp (Exim 4.86_2) (envelope-from ) id 1hgsbW-0003VN-4p for qemu-devel@nongnu.org; Fri, 28 Jun 2019 11:16:05 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1hgsbL-0006Ik-3Y for qemu-devel@nongnu.org; Fri, 28 Jun 2019 11:15:49 -0400 Received: from mx1.redhat.com ([209.132.183.28]:58246) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1hgsbE-00068a-Cp; Fri, 28 Jun 2019 11:15:40 -0400 Received: from smtp.corp.redhat.com (int-mx01.intmail.prod.int.phx2.redhat.com [10.5.11.11]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id E52E83087921; Fri, 28 Jun 2019 15:15:18 +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 870C16013D; Fri, 28 Jun 2019 15:15:15 +0000 (UTC) Date: Fri, 28 Jun 2019 17:15:14 +0200 From: Kevin Wolf To: Alberto Garcia Message-ID: <20190628151514.GQ5179@dhcp-200-226.str.redhat.com> References: <20190627135914.xlzohrdwr6mz2aq3@perseus.local> <4453cfc4-cff7-c004-1f4c-7cab462e4661@virtuozzo.com> <434b102d-9d8e-ccc2-cb53-7f49a3fbd6fb@virtuozzo.com> <20190628145708.GN5179@dhcp-200-226.str.redhat.com> <7452ca4a-c552-a912-a865-d99aaad99488@virtuozzo.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 2.79 on 10.5.11.11 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.45]); Fri, 28 Jun 2019 15:15:24 +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 17:10 hat Alberto Garcia geschrieben: > On Fri 28 Jun 2019 05:03:13 PM CEST, Denis Lunev wrote: > > On 6/28/19 6:02 PM, Alberto Garcia wrote: > >>>>> Please note, I am not talking now about your case with COW. Here the > >>>>> allocation is performed on the sub-cluster basis, i.e. the abscence of > >>>>> the sub-cluster in the image means hole on that offset. This is > >>>>> important difference. > >>>> I mentioned the possibility that if you have a case like 2MB / 64KB > >>>> and you write to an empty cluster then you could allocate the > >>>> necessary subclusters, and additionally fallocate() the space of the > >>>> whole cluster (2MB) in order to try to keep it contiguous. > >>>> > >>>> With this we would lose the space saving advantage of having > >>>> subclusters. But perhaps that would work for smaller cluster sizes > >>>> (it would mitigate the fragmentation problem). > >>> There seem to be use cases for both ways. So does this need to be an > >>> option? > >> Probably a runtime option, or a heuristic that decides what to do > >> depending on the cluster size. > > no, I think that this should be on-disk option as this affects > > allocation strategy. > > But why does it need to be stored on-disk? It should be theoretically > possible to switch between on strategy and the other at runtime (not > that it would make sense though). I think it makes sense to store the default in the image and allow it to be overridden at runtime, similar to lazy_refcounts. Kevin