Especially 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 a 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 size. 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 time a simple "qemu-img map" takes.
Without an extent size hint:
$ ./qemu-img create -f raw -o extent_size_hint=0 ~/tmp/test.raw 10G
Formatting '/home/kwolf/tmp/test.raw', fmt=raw size=10737418240 extent_size_hint=0
$ ./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 (starting 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 (starting 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=1M ~/tmp/test.raw 10G
Formatting '/home/kwolf/tmp/test.raw', fmt=raw size=10737418240 extent_size_hint=1048576
$ ./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 (starting 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 (starting 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 <kwolf@redhat.com>
Message-Id: <20200707142329.48303-1-kwolf@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Signed-off-by: Max Reitz <mreitz@redhat.com>
Message-id: 20191107163708.833192-22-mreitz@redhat.com
[mreitz: Also disable 273]
Signed-off-by: Max Reitz <mreitz@redhat.com>
Just rm will not delete external data files. Use _rm_test_img every
time we delete a test image.
(In the process, clean up the indentation of every _cleanup() this patch
touches.)
((Also, use quotes consistently. I am happy to see unquoted instances
like "rm -rf $TEST_DIR/..." go.))
Signed-off-by: Max Reitz <mreitz@redhat.com>
Reviewed-by: Maxim Levitsky <mlevitsk@redhat.com>
Message-id: 20191107163708.833192-16-mreitz@redhat.com
Signed-off-by: Max Reitz <mreitz@redhat.com>
Tests should not overwrite all user-supplied image options, but only add
to it (which will effectively overwrite conflicting values). Accomplish
this by passing options to _make_test_img via -o instead of $IMGOPTS.
For some tests, there is no functional change because they already only
appended options to IMGOPTS. For these, this patch is just a
simplification.
For others, this is a change, so they now heed user-specified $IMGOPTS.
Some of those tests do not work with all image options, though, so we
need to disable them accordingly.
Signed-off-by: Max Reitz <mreitz@redhat.com>
Reviewed-by: Maxim Levitsky <mlevitsk@redhat.com>
Message-id: 20191107163708.833192-12-mreitz@redhat.com
Signed-off-by: Max Reitz <mreitz@redhat.com>
bash is installed in a different directory on non-Linux systems like
FreeBSD. Do not hard-code /bin/bash here so that the tests can run
there, too.
Reviewed-by: Eric Blake <eblake@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Acked-by: Christian Borntraeger <borntraeger@de.ibm.com>
Message-Id: <20190502084506.8009-4-thuth@redhat.com>
Signed-off-by: Thomas Huth <thuth@redhat.com>
Test that preallocating metadata results in a somewhat larger qcow2
file, but preallocating data only affects the disk usage of the data
file and the qcow2 file stays small.
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
