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 EA55EC4321A for ; Fri, 28 Jun 2019 15:28:54 +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 BFD232064A for ; Fri, 28 Jun 2019 15:28:54 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org BFD232064A 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]:33286 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.86_2) (envelope-from ) id 1hgso2-0004yD-0z for qemu-devel@archiver.kernel.org; Fri, 28 Jun 2019 11:28:54 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:51397) by lists.gnu.org with esmtp (Exim 4.86_2) (envelope-from ) id 1hgsV8-0006HA-VI for qemu-devel@nongnu.org; Fri, 28 Jun 2019 11:09:24 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1hgsV7-0000W2-TW for qemu-devel@nongnu.org; Fri, 28 Jun 2019 11:09:22 -0400 Received: from mx1.redhat.com ([209.132.183.28]:41120) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1hgsV4-0000Pa-8t; Fri, 28 Jun 2019 11:09:18 -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 0502A6EB95; Fri, 28 Jun 2019 15:09:14 +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 A316626E58; Fri, 28 Jun 2019 15:09:12 +0000 (UTC) Date: Fri, 28 Jun 2019 17:09:11 +0200 From: Kevin Wolf To: Alberto Garcia Message-ID: <20190628150911.GP5179@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> 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 [10.5.110.25]); Fri, 28 Jun 2019 15:09:14 +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 17:02 hat Alberto Garcia geschrieben: > On Fri 28 Jun 2019 04:57:08 PM CEST, Kevin Wolf wrote: > > Am 28.06.2019 um 16:43 hat Alberto Garcia geschrieben: > >> On Thu 27 Jun 2019 06:05:55 PM CEST, Denis Lunev 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. How would the heuristic decide whether the user wants to save disk space or whether they consider avoiding fragmentation (i.e. performance) more important? Kevin