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=-3.8 required=3.0 tests=BAYES_00, 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 31729C433B4 for ; Mon, 19 Apr 2021 17:14:06 +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 53238611F0 for ; Mon, 19 Apr 2021 17:14:05 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 53238611F0 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=kamp.de Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Received: from localhost ([::1]:41712 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1lYXTI-0007Pi-FT for qemu-devel@archiver.kernel.org; Mon, 19 Apr 2021 13:14:04 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:49380) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1lYXRd-0004Yd-ST; Mon, 19 Apr 2021 13:12:21 -0400 Received: from kerio.kamp.de ([195.62.97.192]:34853) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1lYXRb-0007by-K3; Mon, 19 Apr 2021 13:12:21 -0400 X-Footer: a2FtcC5kZQ== Received: from [192.168.178.98] ([79.200.86.192]) (authenticated user pl@kamp.de) by kerio.kamp.de with ESMTPSA (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256 bits)); Mon, 19 Apr 2021 19:12:09 +0200 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable From: Peter Lieven Mime-Version: 1.0 (1.0) Subject: Re: [RFC PATCH 0/2] qemu-img convert: Fix sparseness detection Date: Mon, 19 Apr 2021 19:12:15 +0200 Message-Id: References: In-Reply-To: To: Kevin Wolf X-Mailer: iPhone Mail (18D70) Received-SPF: pass client-ip=195.62.97.192; envelope-from=pl@kamp.de; helo=kerio.kamp.de X-Spam_score_int: -18 X-Spam_score: -1.9 X-Spam_bar: - X-Spam_report: (-1.9 / 5.0 requ) BAYES_00=-1.9, 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" Von meinem iPhone gesendet > Am 19.04.2021 um 14:31 schrieb Kevin Wolf : >=20 > =EF=BB=BFAm 19.04.2021 um 11:13 hat Peter Lieven geschrieben: >>=20 >>=20 >>>> Am 19.04.2021 um 10:36 schrieb Peter Lieven : >>>=20 >>>=20 >>>=20 >>>> Am 15.04.2021 um 17:22 schrieb Kevin Wolf : >>>>=20 >>>> 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). >>>>=20 >>>> https://bugzilla.redhat.com/show_bug.cgi?id=3D1882917 >>>>=20 >>>> 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? >>>>=20 >>>> Of course, it would be possible to have a more complete fix like lookin= g >>>> forward a few blocks more before writing data, but that would probably >>>> not be entirely trivial because you would have to merge blocks with ZER= O >>>> block status with DATA blocks that contain only zeros. I'm not sure if >>>> it's worth this complication of the code. >>>=20 >>> I will try to look into this asap. >>=20 >> Besides from the reproducer described in the ticket, I retried my old >> conversion test in our environment: >>=20 >> Before commit 8dcd3c9b91: reads 4608 writes 14959 >> After commit 8dcd3c9b91: reads 0 writes 14924 >> With Kevins patch: reads 110 writes 14924 >>=20 >> I think this is a good result if it avoids other issues. >=20 > Sounds like a promising way to make the tradeoff. Thanks for testing! is this sth for 6.0-rc4? Peter