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Fri, 10 Jul 2020 16:12:05 +0000 (UTC) Subject: Re: [PATCH for-5.1] file-posix: Mitigate file fragmentation with extent size hints To: Kevin Wolf , qemu-block@nongnu.org References: <20200707142329.48303-1-kwolf@redhat.com> <20200707161741.GG7002@linux.fritz.box> 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: <451ed32d-72e8-0238-8793-f5a80ae991c4@redhat.com> Date: Fri, 10 Jul 2020 18:12:04 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.9.0 MIME-Version: 1.0 In-Reply-To: <20200707161741.GG7002@linux.fritz.box> X-Scanned-By: MIMEDefang 2.79 on 10.5.11.14 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="Rd55P4OmxNat95E0BBHNw3m88C4tcEMlC" Received-SPF: pass client-ip=207.211.31.81; envelope-from=mreitz@redhat.com; helo=us-smtp-delivery-1.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/07/09 23:35:58 X-ACL-Warn: Detected OS = Linux 2.2.x-3.x [generic] [fuzzy] X-Spam_score_int: -30 X-Spam_score: -3.1 X-Spam_bar: --- X-Spam_report: (-3.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-1, 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=-0.01, RCVD_IN_MSPIKE_WL=-0.01, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=unavailable autolearn_force=no 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: qemu-devel@nongnu.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) --Rd55P4OmxNat95E0BBHNw3m88C4tcEMlC Content-Type: multipart/mixed; boundary="cwY92oLKOF5Rt91MZGoqMUruUHWHC4eFX" --cwY92oLKOF5Rt91MZGoqMUruUHWHC4eFX Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: quoted-printable On 07.07.20 18:17, Kevin Wolf wrote: > Am 07.07.2020 um 16:23 hat Kevin Wolf geschrieben: >> Espeically when O_DIRECT is used with image files so that the page cache >> indirection can't cause a merge of allocating requests, the file will >> fragment on the file system layer, with a potentially very small >> fragment size (this depends on the requests the guest sent). >> >> On Linux, fragmentation can be reduced by setting an extent size hint >> when creating the file (at least on XFS, it can't be set any more after >> the first extent has been allocated), basically giving raw files a >> "cluster size" for allocation. >> >> This adds an create option to set the extent size hint, and changes the >> default from not setting a hint to setting it to 1 MB. The main reason >> why qcow2 defaults to smaller cluster sizes is that COW becomes more >> expensive, which is not an issue with raw files, so we can choose a >> larger file. The tradeoff here is only potentially wasted disk space. >> >> For qcow2 (or other image formats) over file-posix, the advantage should >> even be greater because they grow sequentially without leaving holes, so >> there won't be wasted space. Setting even larger extent size hints for >> such images may make sense. This can be done with the new option, but >> let's keep the default conservative for now. >> >> The effect is very visible with a test that intentionally creates a >> badly fragmented file with qemu-img bench (the time difference while >> creating the file is already remarkable) and then looks at the number of >> extents and the take a simple "qemu-img map" takes. >> >> Without an extent size hint: >> >> $ ./qemu-img create -f raw -o extent_size_hint=3D0 ~/tmp/test.raw 10= G >> Formatting '/home/kwolf/tmp/test.raw', fmt=3Draw size=3D10737418240 = extent_size_hint=3D0 >> $ ./qemu-img bench -f raw -t none -n -w ~/tmp/test.raw -c 1000000 -S= 8192 -o 0 >> Sending 1000000 write requests, 4096 bytes each, 64 in parallel (sta= rting at offset 0, step size 8192) >> Run completed in 25.848 seconds. >> $ ./qemu-img bench -f raw -t none -n -w ~/tmp/test.raw -c 1000000 -S= 8192 -o 4096 >> Sending 1000000 write requests, 4096 bytes each, 64 in parallel (sta= rting at offset 4096, step size 8192) >> Run completed in 19.616 seconds. >> $ filefrag ~/tmp/test.raw >> /home/kwolf/tmp/test.raw: 2000000 extents found >> $ time ./qemu-img map ~/tmp/test.raw >> Offset Length Mapped to File >> 0 0x1e8480000 0 /home/kwolf/tmp/test= .raw >> >> real 0m1,279s >> user 0m0,043s >> sys 0m1,226s >> >> With the new default extent size hint of 1 MB: >> >> $ ./qemu-img create -f raw -o extent_size_hint=3D1M ~/tmp/test.raw 1= 0G >> Formatting '/home/kwolf/tmp/test.raw', fmt=3Draw size=3D10737418240 = extent_size_hint=3D1048576 >> $ ./qemu-img bench -f raw -t none -n -w ~/tmp/test.raw -c 1000000 -S= 8192 -o 0 >> Sending 1000000 write requests, 4096 bytes each, 64 in parallel (sta= rting at offset 0, step size 8192) >> Run completed in 11.833 seconds. >> $ ./qemu-img bench -f raw -t none -n -w ~/tmp/test.raw -c 1000000 -S= 8192 -o 4096 >> Sending 1000000 write requests, 4096 bytes each, 64 in parallel (sta= rting at offset 4096, step size 8192) >> Run completed in 10.155 seconds. >> $ filefrag ~/tmp/test.raw >> /home/kwolf/tmp/test.raw: 178 extents found >> $ time ./qemu-img map ~/tmp/test.raw >> Offset Length Mapped to File >> 0 0x1e8480000 0 /home/kwolf/tmp/test= .raw >> >> real 0m0,061s >> user 0m0,040s >> sys 0m0,014s >> >> Signed-off-by: Kevin Wolf >=20 > I also need to squash in a few trivial qemu-iotests updates, for which I > won't send a v2: The additional specifications in 243 make it print a warning on tmpfs (because the option doesn=E2=80=99t work there). I suppose the same may be= true on other filesystems as well. Should it be filtered out? Max --cwY92oLKOF5Rt91MZGoqMUruUHWHC4eFX-- --Rd55P4OmxNat95E0BBHNw3m88C4tcEMlC Content-Type: application/pgp-signature; name="signature.asc" Content-Description: OpenPGP digital signature Content-Disposition: attachment; filename="signature.asc" -----BEGIN PGP SIGNATURE----- iQEzBAEBCAAdFiEEkb62CjDbPohX0Rgp9AfbAGHVz0AFAl8Ik1QACgkQ9AfbAGHV z0Ds5AgAi7Mvr1uQbZ0r5ww5hOrfurAk4xkpyx+xf/cMBPUpStu8nRdldA56/Vfw C59oKSudjY29LNrSzmedvxZOComNN5OOYX2Ama28IUano1kIU2uW3POo9eBbxh9H M3o56wgPxwkqgcEFwWfl2qrioy245dZAc/Ixw69VBmjizG3Kfs4F5wDfBvv3jpXE XxFVOxGXTUqpMjjPRSIb7SGUSsUmsYkvEw2YrN342SnXjK7+F6JKbTmREX4NKyxr l33KL+y87Z3LkjHwF5nMXfMt0vyOgQGtolLu2MOK9ul9heqI1VN6ON3fT/dNbYoy +R9MStQ8VZ0zFLr7mZYBTslULhFN7w== =9HhK -----END PGP SIGNATURE----- --Rd55P4OmxNat95E0BBHNw3m88C4tcEMlC--