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=-5.0 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE, SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=ham 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 8B4CACA9EA0 for ; Tue, 22 Oct 2019 09:29:48 +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 5572A2064B for ; Tue, 22 Oct 2019 09:29:48 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="eVjIdfDs" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 5572A2064B 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]:52184 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1iMqU7-0005V4-Gu for qemu-devel@archiver.kernel.org; Tue, 22 Oct 2019 05:29:47 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:54164) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1iMqT3-0004Qr-Hu for qemu-devel@nongnu.org; Tue, 22 Oct 2019 05:28:42 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1iMqT2-0002im-EL for qemu-devel@nongnu.org; Tue, 22 Oct 2019 05:28:41 -0400 Received: from us-smtp-2.mimecast.com ([207.211.31.81]:35657 helo=us-smtp-delivery-1.mimecast.com) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1iMqT2-0002ht-9N for qemu-devel@nongnu.org; Tue, 22 Oct 2019 05:28:40 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1571736518; 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:autocrypt:autocrypt; bh=EQR9nG4elJz+4QBIcXjW+L7/ihX1GDQURAjCVrYlfC8=; b=eVjIdfDs2xmLnQfZq6QkZcEeg+GF3Ir1JbEHiPok1/71vl0idKivBU1WjfnTKMJ0Y8rztK 3lqOxsM5X+0ZrCJ/IEKD+YoTc1TXqh8Cpw3Hwdp//QuQwwj1PIoD3RmYx6AEGwvUASwfom LuZNbGqgaaDayCVFIwiI8fv1SgmM8Ys= 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-71-jhbhz5-ZMyqJTNYsZbPJvg-1; Tue, 22 Oct 2019 05:28:36 -0400 X-MC-Unique: jhbhz5-ZMyqJTNYsZbPJvg-1 Received: from smtp.corp.redhat.com (int-mx04.intmail.prod.int.phx2.redhat.com [10.5.11.14]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 299B6476; Tue, 22 Oct 2019 09:28:34 +0000 (UTC) Received: from dresden.str.redhat.com (ovpn-117-215.ams2.redhat.com [10.36.117.215]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 65A345DE5B; Tue, 22 Oct 2019 09:28:29 +0000 (UTC) Subject: Re: [PATCH v5 1/4] block: support compressed write at generic layer To: Andrey Shinkevich , qemu-devel@nongnu.org, qemu-block@nongnu.org References: <1571603828-185910-1-git-send-email-andrey.shinkevich@virtuozzo.com> <1571603828-185910-2-git-send-email-andrey.shinkevich@virtuozzo.com> From: Max Reitz Autocrypt: addr=mreitz@redhat.com; prefer-encrypt=mutual; keydata= mQENBFXOJlcBCADEyyhOTsoa/2ujoTRAJj4MKA21dkxxELVj3cuILpLTmtachWj7QW+TVG8U /PsMCFbpwsQR7oEy8eHHZwuGQsNpEtNC2G/L8Yka0BIBzv7dEgrPzIu+W3anZXQW4702+uES U29G8TP/NGfXRRHGlbBIH9KNUnOSUD2vRtpOLXkWsV5CN6vQFYgQfFvmp5ZpPeUe6xNplu8V mcTw8OSEDW/ZnxJc8TekCKZSpdzYoxfzjm7xGmZqB18VFwgJZlIibt1HE0EB4w5GsD7x5ekh awIe3RwoZgZDLQMdOitJ1tUc8aqaxvgA4tz6J6st8D8pS//m1gAoYJWGwwIVj1DjTYLtABEB AAG0HU1heCBSZWl0eiA8bXJlaXR6QHJlZGhhdC5jb20+iQFTBBMBCAA9AhsDBQkSzAMABQsJ CAcCBhUICQoLAgQWAgMBAh4BAheABQJVzie5FRhoa3A6Ly9rZXlzLmdudXBnLm5ldAAKCRD0 B9sAYdXPQDcIB/9uNkbYEex1rHKz3mr12uxYMwLOOFY9fstP5aoVJQ1nWQVB6m2cfKGdcRe1 2/nFaHSNAzT0NnKz2MjhZVmcrpyd2Gp2QyISCfb1FbT82GMtXFj1wiHmPb3CixYmWGQUUh+I AvUqsevLA+WihgBUyaJq/vuDVM1/K9Un+w+Tz5vpeMidlIsTYhcsMhn0L9wlCjoucljvbDy/ 8C9L2DUdgi3XTa0ORKeflUhdL4gucWoAMrKX2nmPjBMKLgU7WLBc8AtV+84b9OWFML6NEyo4 4cP7cM/07VlJK53pqNg5cHtnWwjHcbpGkQvx6RUx6F1My3y52vM24rNUA3+ligVEgPYBuQEN BFXOJlcBCADAmcVUNTWT6yLWQHvxZ0o47KCP8OcLqD+67T0RCe6d0LP8GsWtrJdeDIQk+T+F xO7DolQPS6iQ6Ak2/lJaPX8L0BkEAiMuLCKFU6Bn3lFOkrQeKp3u05wCSV1iKnhg0UPji9V2 W5eNfy8F4ZQHpeGUGy+liGXlxqkeRVhLyevUqfU0WgNqAJpfhHSGpBgihUupmyUg7lfUPeRM DzAN1pIqoFuxnN+BRHdAecpsLcbR8sQddXmDg9BpSKozO/JyBmaS1RlquI8HERQoe6EynJhd 64aICHDfj61rp+/0jTIcevxIIAzW70IadoS/y3DVIkuhncgDBvGbF3aBtjrJVP+5ABEBAAGJ ASUEGAEIAA8FAlXOJlcCGwwFCRLMAwAACgkQ9AfbAGHVz0CbFwf9F/PXxQR9i4N0iipISYjU sxVdjJOM2TMut+ZZcQ6NSMvhZ0ogQxJ+iEQ5OjnIputKvPVd5U7WRh+4lF1lB/NQGrGZQ1ic alkj6ocscQyFwfib+xIe9w8TG1CVGkII7+TbS5pXHRxZH1niaRpoi/hYtgzkuOPp35jJyqT/ /ELbqQTDAWcqtJhzxKLE/ugcOMK520dJDeb6x2xVES+S5LXby0D4juZlvUj+1fwZu+7Io5+B bkhSVPb/QdOVTpnz7zWNyNw+OONo1aBUKkhq2UIByYXgORPFnbfMY7QWHcjpBVw9MgC4tGeF R4bv+1nAMMxKmb5VvQCExr0eFhJUAHAhVg== Message-ID: <408ef2ab-1f6c-2c9f-ad50-92269c20fb27@redhat.com> Date: Tue, 22 Oct 2019 11:28:28 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.1.1 MIME-Version: 1.0 In-Reply-To: <1571603828-185910-2-git-send-email-andrey.shinkevich@virtuozzo.com> X-Scanned-By: MIMEDefang 2.79 on 10.5.11.14 X-Mimecast-Spam-Score: 0 Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="PWMb4ANxS6m6ixz3dh6bEPayGQxa0TtMM" X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] [fuzzy] X-Received-From: 207.211.31.81 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, fam@euphon.net, vsementsov@virtuozzo.com, armbru@redhat.com, stefanha@redhat.com, den@openvz.org Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" This is an OpenPGP/MIME signed message (RFC 4880 and 3156) --PWMb4ANxS6m6ixz3dh6bEPayGQxa0TtMM Content-Type: multipart/mixed; boundary="YnjNuAkRS1GPyADfgxoltB5BdrVBvl4VT" --YnjNuAkRS1GPyADfgxoltB5BdrVBvl4VT Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: quoted-printable On 20.10.19 22:37, Andrey Shinkevich wrote: > To inform the block layer about writing all the data compressed, we > introduce the 'compress' command line option. Based on that option, the > written data will be aligned by the cluster size at the generic layer. >=20 > Suggested-by: Roman Kagan > Suggested-by: Vladimir Sementsov-Ogievskiy > Signed-off-by: Andrey Shinkevich > Reviewed-by: Vladimir Sementsov-Ogievskiy > --- > block.c | 20 +++++++++++++++++++- > block/io.c | 13 +++++++++---- > block/qcow2.c | 4 ++++ > blockdev.c | 9 ++++++++- > include/block/block.h | 1 + > include/block/block_int.h | 2 ++ > qapi/block-core.json | 5 ++++- > qemu-options.hx | 6 ++++-- > 8 files changed, 51 insertions(+), 9 deletions(-) The problem with compression is that there are such tight constraints on it that it can really only work for very defined use cases. Those constraints are: - Only write whole clusters, - Clusters can be written to only once. The first point is addressed in this patch by setting request_alignment. But I don=E2=80=99t see how the second one can be addressed. Well, maybe = by allowing it in all drivers that support compression. But if I just look at qcow2, that isn=E2=80=99t going to be trivial: You need to allocate a completely new cluster where you write the data (in case it grows), and thus you leave behind a hole, which kind of defeats the purpose of compression. (For demonstration: $ ./qemu-img create -f qcow2 test.qcow2 64M Formatting 'test.qcow2', fmt=3Dqcow2 size=3D67108864 cluster_size=3D65536 lazy_refcounts=3Doff refcount_bits=3D16 $ x86_64-softmmu/qemu-system-x86_64 \ -blockdev "{'node-name': 'drv0', 'driver': 'qcow2', 'compress': true, 'file': {'driver': 'file', 'filename': 'test.qcow2'}}" \ -monitor stdio QEMU 4.1.50 monitor - type 'help' for more information (qemu) qemu-io drv0 "write -P 42 0 64k" wrote 65536/65536 bytes at offset 0 64 KiB, 1 ops; 00.02 sec (4.055 MiB/sec and 64.8793 ops/sec) (qemu) qemu-io drv0 "write -P 23 0 64k" write failed: Input/output error ) Compression really only works when you fully write all of an image exactly once; i.e. as the qemu-img convert or as a backup target. For both cases we already have a compression option. So I=E2=80=99m wondering = where this new option is really useful. (You do add a test for stream, but I don=E2=80=99t know whether that=E2=80= =99s really a good example, see my response there.) Max --YnjNuAkRS1GPyADfgxoltB5BdrVBvl4VT-- --PWMb4ANxS6m6ixz3dh6bEPayGQxa0TtMM Content-Type: application/pgp-signature; name="signature.asc" Content-Description: OpenPGP digital signature Content-Disposition: attachment; filename="signature.asc" -----BEGIN PGP SIGNATURE----- iQEzBAEBCAAdFiEEkb62CjDbPohX0Rgp9AfbAGHVz0AFAl2uy7wACgkQ9AfbAGHV z0BRrggAiuA7CbJH3w0BnvVDSkvEh4TUeO+/dWH7siApjaT4MAFswz54YklVEDhD INdNQnMqJabbjacSKDBpZlHBTZ+/+vJ7gKMh5Maa8A0oT7VTVMxI3kXpexrieAIb +DKfscmHafaqv2F1hFxHVbnRfXZdN6L+K0q1xMsXSO+Qc371oDDVNIuMHMhW7byc qL48KoaMqrE33FKsPix+ezxgOfXPnVM1Qylr9qkRVOd92jebTzJTYdfmnOlZc7Ad bsFIqMtb5dEKgq7jYrvYF5hlM9H8juVWySfsEPX5IpqsiMDx2DYfpCm+a59YCT8D w4tCBVYPu2ya40T3l9ugNK+sCgtnog== =j8Hc -----END PGP SIGNATURE----- --PWMb4ANxS6m6ixz3dh6bEPayGQxa0TtMM--