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=-2.0 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_1 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 077B8CA9EAF for ; Thu, 24 Oct 2019 13:53:36 +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 C3FF021655 for ; Thu, 24 Oct 2019 13:53:35 +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="ir+H9j7q" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org C3FF021655 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]:43228 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1iNdYT-0007gy-DZ for qemu-devel@archiver.kernel.org; Thu, 24 Oct 2019 09:53:33 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:59988) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1iNdTR-0003cA-FF for qemu-devel@nongnu.org; Thu, 24 Oct 2019 09:48:22 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1iNdTO-0008AU-MO for qemu-devel@nongnu.org; Thu, 24 Oct 2019 09:48:20 -0400 Received: from us-smtp-2.mimecast.com ([207.211.31.81]:54891 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 1iNdTO-00088v-4F for qemu-devel@nongnu.org; Thu, 24 Oct 2019 09:48:18 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1571924894; 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=Hk6Wg6UfVi/TnRspPYhEUtS2XkIIu/9oHcDDY5nokkc=; b=ir+H9j7qmR0xtOQBkyA9MuJ0PPDAKpAtHK3GWkIproP8zmDKcmhP2KhGjeKC8ShGHp41L+ rbPQjcmqFtuJ3KXC3o0zJU9+nP5SgF2+D2YNO1I6be/fJtXxhhRXCEUNKtPVwMirUANiOi jdH5P0Vd0QgEn2Tn6btYVrKreiyRn2U= 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-339-AR61IUxpOwWtCj_Bg92cPQ-1; Thu, 24 Oct 2019 09:48:11 -0400 X-MC-Unique: AR61IUxpOwWtCj_Bg92cPQ-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 BDB3480183D; Thu, 24 Oct 2019 13:48:09 +0000 (UTC) Received: from dresden.str.redhat.com (ovpn-117-205.ams2.redhat.com [10.36.117.205]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 6BA725D9D5; Thu, 24 Oct 2019 13:48:07 +0000 (UTC) Subject: Re: [PATCH v5 1/4] block: support compressed write at generic layer To: Andrey Shinkevich , Vladimir Sementsov-Ogievskiy , "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> <408ef2ab-1f6c-2c9f-ad50-92269c20fb27@redhat.com> <787da788-9aca-2110-a092-b63ef498a9fa@redhat.com> <1088f0ff-d882-083f-705c-95c08bdc486f@redhat.com> <4fd89d2a-94aa-6f2d-ed7d-7633356e5163@redhat.com> <539e7d9e-0cb7-fdb7-f376-1648361ec2f3@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: <8828d08f-79aa-f3a6-4387-f1423a8b7d70@redhat.com> Date: Thu, 24 Oct 2019 15:48:05 +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: <539e7d9e-0cb7-fdb7-f376-1648361ec2f3@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="lcqM5PwKqt9YICTYHMH9M2gB4ervX1ZWN" 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" , Denis Lunev , "armbru@redhat.com" , "stefanha@redhat.com" 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) --lcqM5PwKqt9YICTYHMH9M2gB4ervX1ZWN Content-Type: multipart/mixed; boundary="vrEpoaTwFtTuRqpN20PsA5Nmdh3qs7idV" --vrEpoaTwFtTuRqpN20PsA5Nmdh3qs7idV Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: quoted-printable On 24.10.19 14:56, Andrey Shinkevich wrote: >=20 >=20 > On 24/10/2019 12:34, Max Reitz wrote: >> On 22.10.19 15:53, Andrey Shinkevich wrote: >> >> [...] >> >>> If the support of COW for compressed writes is found feasible, will it >>> make a sense to implement? Then this series will follow. >> >> Hm, what exactly do you mean by support of COW for compressed writes? >> >=20 > I spoke in terms of the commit message with the following ID: >=20 > b0b6862e5e1a1394e0ab3d5da94ba8b0da8664e2 >=20 > "qcow2: Fail write_compressed when overwriting data" >=20 > "...qcow2_write_compressed() doesn't perform COW as it would have to do..= ." >=20 > So, I suggest that we implement writing compressed data to the allocated= =20 > clusters rather than qcow2_alloc_compressed_cluster_offset() returns the= =20 > error. Particularly, when it comes to NBD server connection failure for= =20 > writhing a compressed cluster, it may not be rewritten after the=20 > connection is restored. > Are there any issues with that implementation idea? Well, the COW in that commit is meant differently, because it refers to the COW that=E2=80=99s required when writing to a cluster shared by an inte= rnal snapshot. OTOH, you could say that all compressed writes to a cluster that is already allocated would need to do COW because we=E2=80=99d always have to = fully rewrite that cluster in an RMW cycle. I don=E2=80=99t see how letting qcow2_alloc_compressed_cluster_offset() use= the existing cluster would solve the problem, though. You=E2=80=99d generally = need to allocate a new cluster; or attempt to reuse the existing space in a compressed cluster. Max --vrEpoaTwFtTuRqpN20PsA5Nmdh3qs7idV-- --lcqM5PwKqt9YICTYHMH9M2gB4ervX1ZWN Content-Type: application/pgp-signature; name="signature.asc" Content-Description: OpenPGP digital signature Content-Disposition: attachment; filename="signature.asc" -----BEGIN PGP SIGNATURE----- iQEzBAEBCAAdFiEEkb62CjDbPohX0Rgp9AfbAGHVz0AFAl2xq5UACgkQ9AfbAGHV z0A01Qf8Dsa7NS79rKBSw3aha7lWCmbG9T7HHaDqMfrhv6S8Nuru1yGR2ySgIyIo X4i67ZqRl3/CRrwZmnqKFQ1IZ3czJNneqPlRq7rzxfcaS+umPbu9L4iHbwEzlFT5 bZfztHeI9d4OOD9LocXl4itY2N9LtcxVkMsEGOsV+cFns56eH0TBW3OLc6ozd2fd euwQS6EBuoxlg9HvBu3cs3vAlNNdauSdIysayxIOT0Yt24Wfha+vSJ/+j8l5N57z 0GM4JvIs0SQYa2f8hRpRk23TYy7CSzbLwJoQQKjdbotXMuuOqzGzNlSqiOkUS4Vl YLgO7UwGHKlF4Kze+itL9yzEuZqLww== =fu5f -----END PGP SIGNATURE----- --lcqM5PwKqt9YICTYHMH9M2gB4ervX1ZWN--