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Mon, 4 Nov 2019 15:14:58 +0000 (UTC) Subject: Re: [RFC 0/3] block/file-posix: Work around XFS bug To: Alberto Garcia , Vladimir Sementsov-Ogievskiy , "qemu-block@nongnu.org" References: <20191025095849.25283-1-mreitz@redhat.com> <02291bca-67d2-ed30-ac34-17641afbe397@virtuozzo.com> <0f75cbcf-e6c7-c74c-972b-22e7760a8b5c@redhat.com> <7ed9b8f0-2d8c-7bac-185e-9a1dd68fcce8@redhat.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: <5b67cf39-0ea1-d205-0e96-7b1148c7df19@redhat.com> Date: Mon, 4 Nov 2019 16:14:56 +0100 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: X-Scanned-By: MIMEDefang 2.79 on 10.5.11.11 X-Mimecast-Spam-Score: 0 Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="98JCLW6VxP32iBmnGhZGOeUqxBdaySizV" X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] [fuzzy] X-Received-From: 207.211.31.120 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: Kevin Wolf , Anton Nefedov , "qemu-devel@nongnu.org" , Stefan Hajnoczi 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) --98JCLW6VxP32iBmnGhZGOeUqxBdaySizV Content-Type: multipart/mixed; boundary="UqOCLkW9V5lKCSQGfk8J0oJ9fn7xRCogH" --UqOCLkW9V5lKCSQGfk8J0oJ9fn7xRCogH Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: quoted-printable On 04.11.19 16:12, Alberto Garcia wrote: > On Mon 04 Nov 2019 03:25:12 PM CET, Max Reitz wrote: >>>>>> So, it's obvious that c8bb23cbdbe32f5c326 is significant for 1M >>>>>> cluster-size, even on rotational disk, which means that previous >>>>>> assumption about calling handle_alloc_space() only for ssd is wrong, >>>>>> we need smarter heuristics.. >>>>>> >>>>>> So, I'd prefer (1) or (2). >>>> >>>> OK. I wonder whether that problem would go away with Berto=E2=80=99s = subcluster >>>> series, though. >>> >>> Catching up with this now. I was told about this last week at the KVM >>> Forum, but if the problems comes with the use of fallocate() and XFS, >>> the I don't think subclusters will solve it. >>> >>> handle_alloc_space() is used to fill a cluster with zeroes when there's >>> COW, and that happens the same with subclusters, just at the subcluster >>> level instead of course. >>> >>> What can happen, if the subcluster size matches the filesystem block >>> size, is that there's no need for any COW and therefore the bug is neve= r >>> triggered. But that's not quite the same as a fix :-) >> >> No, what I meant was that the original problem that led to c8bb23cbdbe >> would go away. >=20 > Ah, right. Not quite, according to my numbers: >=20 > |--------------+----------------+-----------------+-------------| > | Cluster size | subclusters=3Don | subclusters=3Doff | fallocate() | > |--------------+----------------+-----------------+-------------| > | 256 KB | 10182 IOPS | 966 IOPS | 14007 IOPS | > | 512 KB | 7919 IOPS | 563 IOPS | 13442 IOPS | > | 1024 KB | 5050 IOPS | 465 IOPS | 13887 IOPS | > | 2048 KB | 2465 IOPS | 271 IOPS | 13885 IOPS | > |--------------+----------------+-----------------+-------------| >=20 > There's obviously no backing image, and only the last column uses > handle_alloc_space() / fallocate(). Thanks for providing some numbers! It was my impression, too, that subclusters wouldn=E2=80=99t solve it. But= it didn=E2=80=99t seem like that big of a difference to me. Did you run this = with aio=3Dnative? (Because that=E2=80=99s where we have the XFS problem) Max --UqOCLkW9V5lKCSQGfk8J0oJ9fn7xRCogH-- --98JCLW6VxP32iBmnGhZGOeUqxBdaySizV Content-Type: application/pgp-signature; name="signature.asc" Content-Description: OpenPGP digital signature Content-Disposition: attachment; filename="signature.asc" -----BEGIN PGP SIGNATURE----- iQEzBAEBCAAdFiEEkb62CjDbPohX0Rgp9AfbAGHVz0AFAl3AQHEACgkQ9AfbAGHV z0CB7Qf/d7/3vCb4tTxpAOyEktDN7DeObB+Psu1Fonw1AW+/M1ASeQ+VARibFXXF fDgBTu8qlO6j+No1tD/CPtk+8DNPnENYu5+SRKem4PcI+kC7nKuYNZVOvxVRkfyI DO+DpoaZd6goYrFm3dYrOC+gQdTNSGMOue0seMX2agXr0lwlwn0cGqnFBS1HrV5G wcmIDMiNbQw1qhisdr47vg3HSzygCNbj7OqkVPXz2AXIFSdZmIitm3OD2E6JikYm rYIkcjE6TsAC3hzQU4g/oJ5evmWJopGF00MgQWFkwxQVK/jeoqt/FtKmf3Hvrrqq TL5hSCFAgKKWJkz+JSj7t+5UpFbe8A== =ITTi -----END PGP SIGNATURE----- --98JCLW6VxP32iBmnGhZGOeUqxBdaySizV--