From nobody Wed Apr 16 03:25:21 2025 Delivered-To: importer@patchew.org Received-SPF: pass (zoho.com: domain of gnu.org designates 209.51.188.17 as permitted sender) client-ip=209.51.188.17; envelope-from=qemu-devel-bounces+importer=patchew.org@nongnu.org; helo=lists.gnu.org; Authentication-Results: mx.zohomail.com; spf=pass (zoho.com: domain of gnu.org designates 209.51.188.17 as permitted sender) smtp.mailfrom=qemu-devel-bounces+importer=patchew.org@nongnu.org; dmarc=fail(p=none dis=none) header.from=redhat.com Return-Path: Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) by mx.zohomail.com with SMTPS id 1553616072606425.22234043284004; Tue, 26 Mar 2019 09:01:12 -0700 (PDT) Received: from localhost ([127.0.0.1]:34144 helo=lists.gnu.org) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1h8oVg-0001Aj-C6 for importer@patchew.org; Tue, 26 Mar 2019 12:01:08 -0400 Received: from eggs.gnu.org ([209.51.188.92]:49856) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1h8oNA-0002xt-8G for qemu-devel@nongnu.org; Tue, 26 Mar 2019 11:52:21 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1h8oN6-00051I-4d for qemu-devel@nongnu.org; Tue, 26 Mar 2019 11:52:20 -0400 Received: from mx1.redhat.com ([209.132.183.28]:52782) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1h8oN3-0004yx-5O; Tue, 26 Mar 2019 11:52:13 -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 7577D81E07; Tue, 26 Mar 2019 15:52:12 +0000 (UTC) Received: from linux.fritz.box.com (ovpn-117-65.ams2.redhat.com [10.36.117.65]) by smtp.corp.redhat.com (Postfix) with ESMTP id 585B660141; Tue, 26 Mar 2019 15:52:11 +0000 (UTC) From: Kevin Wolf To: qemu-block@nongnu.org Date: Tue, 26 Mar 2019 16:51:56 +0100 Message-Id: <20190326155157.3719-7-kwolf@redhat.com> In-Reply-To: <20190326155157.3719-1-kwolf@redhat.com> References: <20190326155157.3719-1-kwolf@redhat.com> MIME-Version: 1.0 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 [10.5.110.25]); Tue, 26 Mar 2019 15:52:12 +0000 (UTC) Content-Transfer-Encoding: quoted-printable X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] X-Received-From: 209.132.183.28 Subject: [Qemu-devel] [PULL 6/7] qemu-img: Use BDRV_REQ_NO_FALLBACK for pre-zeroing X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.21 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: kwolf@redhat.com, peter.maydell@linaro.org, qemu-devel@nongnu.org Errors-To: qemu-devel-bounces+importer=patchew.org@nongnu.org Sender: "Qemu-devel" Content-Type: text/plain; charset="utf-8" If qemu-img convert sees that the target image isn't zero-initialised yet, it tries to do an efficient zero write for the whole image first to save the overhead of repeated explicit zero writes during the conversion. Obviously, this provides only an advantage if the pre-zeroing is actually efficient. Otherwise, we can end up writing zeroes slowly while zeroing out the whole image, and then overwrite the same blocks again with real data, potentially doubling the written data. Pass BDRV_REQ_NO_FALLBACK to blk_make_zero() to avoid this case. If we can't efficiently zero out, we'll instead write explicit zeroes only if there is no data to be written to a block. Signed-off-by: Kevin Wolf Acked-by: Eric Blake --- qemu-img.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/qemu-img.c b/qemu-img.c index 5fac840742..8ee63daeae 100644 --- a/qemu-img.c +++ b/qemu-img.c @@ -1932,7 +1932,7 @@ static int convert_do_copy(ImgConvertState *s) if (!s->has_zero_init && !s->target_has_backing && bdrv_can_write_zeroes_with_unmap(blk_bs(s->target))) { - ret =3D blk_make_zero(s->target, BDRV_REQ_MAY_UNMAP); + ret =3D blk_make_zero(s->target, BDRV_REQ_MAY_UNMAP | BDRV_REQ_NO_= FALLBACK); if (ret =3D=3D 0) { s->has_zero_init =3D true; } --=20 2.20.1