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Tue, 09 Jun 2020 10:09:12 -0400 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-457-052ZW6kvPWuqWUfYoRBPUg-1; Tue, 09 Jun 2020 10:09:07 -0400 Received: from smtp.corp.redhat.com (int-mx02.intmail.prod.int.phx2.redhat.com [10.5.11.12]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id DBD6018A8223; Tue, 9 Jun 2020 14:09:05 +0000 (UTC) Received: from linux.fritz.box.com (ovpn-114-124.ams2.redhat.com [10.36.114.124]) by smtp.corp.redhat.com (Postfix) with ESMTP id 735F79F77; Tue, 9 Jun 2020 14:09:04 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1591711750; 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: content-transfer-encoding:content-transfer-encoding; bh=OSRdD0d6Yp4nIUq+zTQOlRcs3Bdzt2jY+nd3Dosbis8=; b=bPjLollDIPpJwik7cLMYJBcZiqMZmBsojl8R+62Ri84OlBrMw8gyI3e0t0DLfmwONCXIio dp1IykRHsgT2dYubN4ctrs4u+IP5EUcVwnxHQfeWqi7LU565CGvxZQ21sqScDLqj/LN9HM bOMk/OTYf+q5ZNkIFucLxcD/EP8o/oE= X-MC-Unique: 052ZW6kvPWuqWUfYoRBPUg-1 From: Kevin Wolf To: qemu-block@nongnu.org Subject: [PATCH] qcow2: Reduce write_zeroes size in handle_alloc_space() Date: Tue, 9 Jun 2020 16:08:59 +0200 Message-Id: <20200609140859.142230-1-kwolf@redhat.com> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.79 on 10.5.11.12 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Transfer-Encoding: quoted-printable Received-SPF: pass (zohomail.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; Received-SPF: pass client-ip=207.211.31.120; envelope-from=kwolf@redhat.com; helo=us-smtp-1.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/06/09 01:38:49 X-ACL-Warn: Detected OS = Linux 2.2.x-3.x [generic] [fuzzy] X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 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_NONE=-0.0001, RCVD_IN_MSPIKE_H3=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_PASS=-0.001 autolearn=_AUTOLEARN 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: kwolf@redhat.com, anton.nefedov@virtuozzo.com, vsementsov@virtuozzo.com, qemu-devel@nongnu.org, mreitz@redhat.com Errors-To: qemu-devel-bounces+importer=patchew.org@nongnu.org Sender: "Qemu-devel" X-ZohoMail-DKIM: fail (Header signature does not verify) Content-Type: text/plain; charset="utf-8" Since commit c8bb23cbdbe, handle_alloc_space() is called for newly allocated clusters to efficiently initialise the COW areas with zeros if necessary. It skips the whole operation if both start_cow nor end_cow are empty. However, it requests zeroing the whole request size (possibly multiple megabytes) even if only one end of the request actually needs this. This patch reduces the write_zeroes request size in this case so that we don't unnecessarily zero-initialise a region that we're going to overwrite immediately. Signed-off-by: Kevin Wolf --- block/qcow2.c | 16 +++++++++++----- 1 file changed, 11 insertions(+), 5 deletions(-) diff --git a/block/qcow2.c b/block/qcow2.c index 0cd2e6757e..77742877fb 100644 --- a/block/qcow2.c +++ b/block/qcow2.c @@ -2403,6 +2403,8 @@ static int handle_alloc_space(BlockDriverState *bs, Q= CowL2Meta *l2meta) } =20 for (m =3D l2meta; m !=3D NULL; m =3D m->next) { + uint64_t start =3D m->alloc_offset; + uint64_t len =3D m->nb_clusters * s->cluster_size; int ret; =20 if (!m->cow_start.nb_bytes && !m->cow_end.nb_bytes) { @@ -2413,21 +2415,25 @@ static int handle_alloc_space(BlockDriverState *bs,= QCowL2Meta *l2meta) continue; } =20 + if (!m->cow_start.nb_bytes) { + start +=3D m->cow_end.offset; + len -=3D m->cow_end.offset; + } else if (!m->cow_end.nb_bytes) { + len =3D m->cow_start.nb_bytes; + } + /* * instead of writing zero COW buffers, * efficiently zero out the whole clusters */ =20 - ret =3D qcow2_pre_write_overlap_check(bs, 0, m->alloc_offset, - m->nb_clusters * s->cluster_si= ze, - true); + ret =3D qcow2_pre_write_overlap_check(bs, 0, start, len, true); if (ret < 0) { return ret; } =20 BLKDBG_EVENT(bs->file, BLKDBG_CLUSTER_ALLOC_SPACE); - ret =3D bdrv_co_pwrite_zeroes(s->data_file, m->alloc_offset, - m->nb_clusters * s->cluster_size, + ret =3D bdrv_co_pwrite_zeroes(s->data_file, start, len, BDRV_REQ_NO_FALLBACK); if (ret < 0) { if (ret !=3D -ENOTSUP && ret !=3D -EAGAIN) { --=20 2.25.4