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=-3.5 required=3.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS,URIBL_BLOCKED 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 10602C433ED for ; Mon, 19 Apr 2021 12:34:36 +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 8DE4161057 for ; Mon, 19 Apr 2021 12:34:35 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 8DE4161057 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]:60894 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1lYT6o-0006sj-Ka for qemu-devel@archiver.kernel.org; Mon, 19 Apr 2021 08:34:34 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:33184) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1lYT3Y-0005Qh-Vt for qemu-devel@nongnu.org; Mon, 19 Apr 2021 08:31:14 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]:23488) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1lYT3V-0002fx-C3 for qemu-devel@nongnu.org; Mon, 19 Apr 2021 08:31:12 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1618835468; 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=04i1bL/uRjgtCTEXakLiRuXdwtnzlBXr4sID3W1P3J0=; b=G26RS+fWZ33lMgB8FS2ss3NltsovhYl2r8Vn4F7pP49qZ8UNeqsIdVtUEoP+OeJr1hvQf1 1u2WGnHdy4uQFtfVhNWLQgzuVwD4M6zmQHQIzu3gKhOpso8fOau1O5gc98H4IS8eMoLaso jhTx6yaBNflWPO9PdvPyCD0YzfaQi2o= 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-466-7QlH0mSnNsKCQMBeVX_K3g-1; Mon, 19 Apr 2021 08:31:04 -0400 X-MC-Unique: 7QlH0mSnNsKCQMBeVX_K3g-1 Received: from smtp.corp.redhat.com (int-mx05.intmail.prod.int.phx2.redhat.com [10.5.11.15]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id D879C609; Mon, 19 Apr 2021 12:31:03 +0000 (UTC) Received: from merkur.fritz.box (ovpn-114-122.ams2.redhat.com [10.36.114.122]) by smtp.corp.redhat.com (Postfix) with ESMTPS id E627B62466; Mon, 19 Apr 2021 12:31:02 +0000 (UTC) Date: Mon, 19 Apr 2021 14:31:01 +0200 From: Kevin Wolf To: Peter Lieven Subject: Re: [RFC PATCH 0/2] qemu-img convert: Fix sparseness detection Message-ID: References: <20210415152214.279844-1-kwolf@redhat.com> <07747AB5-5BCE-49EE-A3AB-03AA7B6211F8@kamp.de> MIME-Version: 1.0 In-Reply-To: X-Scanned-By: MIMEDefang 2.79 on 10.5.11.15 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=kwolf@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Received-SPF: pass client-ip=170.10.133.124; envelope-from=kwolf@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -27 X-Spam_score: -2.8 X-Spam_bar: -- X-Spam_report: (-2.8 / 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_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: qemu-devel@nongnu.org, qemu-block , Max Reitz Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" Am 19.04.2021 um 11:13 hat Peter Lieven geschrieben: > > > > Am 19.04.2021 um 10:36 schrieb Peter Lieven : > > > > > > > >> Am 15.04.2021 um 17:22 schrieb Kevin Wolf : > >> > >> Peter, three years ago you changed 'qemu-img convert' to sacrifice some > >> sparsification in order to get aligned requests on the target image. At > >> the time, I thought the impact would be small, but it turns out that > >> this can end up wasting gigabytes of storagee (like converting a fully > >> zeroed 10 GB image taking 2.8 GB instead of a few kilobytes). > >> > >> https://bugzilla.redhat.com/show_bug.cgi?id=1882917 > >> > >> I'm not entirely sure how to attack this best since this is a tradeoff, > >> but maybe the approach in this series is still good enough for the case > >> that you wanted to fix back then? > >> > >> Of course, it would be possible to have a more complete fix like looking > >> forward a few blocks more before writing data, but that would probably > >> not be entirely trivial because you would have to merge blocks with ZERO > >> block status with DATA blocks that contain only zeros. I'm not sure if > >> it's worth this complication of the code. > > > > I will try to look into this asap. > > Besides from the reproducer described in the ticket, I retried my old > conversion test in our environment: > > Before commit 8dcd3c9b91: reads 4608 writes 14959 > After commit 8dcd3c9b91: reads 0 writes 14924 > With Kevins patch: reads 110 writes 14924 > > I think this is a good result if it avoids other issues. Sounds like a promising way to make the tradeoff. Thanks for testing! Kevin