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=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 <kw...@redhat.com>
I also need to squash in a few trivial qemu-iotests updates, for which I won't send a v2: diff --git a/tests/qemu-iotests/082.out b/tests/qemu-iotests/082.out index 1b0a75c8f9..0d7c5e8342 100644 --- a/tests/qemu-iotests/082.out +++ b/tests/qemu-iotests/082.out @@ -62,6 +62,7 @@ Supported options: encrypt.ivgen-hash-alg=<str> - Name of IV generator hash algorithm encrypt.key-secret=<str> - ID of secret providing qcow AES key or LUKS passphrase encryption=<bool (on/off)> - Encrypt the image with format 'aes'. (Deprecated in favor of encrypt.format=aes) + extent_size_hint=<size> - Extent size hint for the image file, 0 to disable lazy_refcounts=<bool (on/off)> - Postpone refcount updates nocow=<bool (on/off)> - Turn off copy-on-write (valid only on btrfs) preallocation=<str> - Preallocation mode (allowed values: off, metadata, falloc, full) @@ -86,6 +87,7 @@ Supported options: encrypt.ivgen-hash-alg=<str> - Name of IV generator hash algorithm encrypt.key-secret=<str> - ID of secret providing qcow AES key or LUKS passphrase encryption=<bool (on/off)> - Encrypt the image with format 'aes'. (Deprecated in favor of encrypt.format=aes) + extent_size_hint=<size> - Extent size hint for the image file, 0 to disable lazy_refcounts=<bool (on/off)> - Postpone refcount updates nocow=<bool (on/off)> - Turn off copy-on-write (valid only on btrfs) preallocation=<str> - Preallocation mode (allowed values: off, metadata, falloc, full) @@ -110,6 +112,7 @@ Supported options: encrypt.ivgen-hash-alg=<str> - Name of IV generator hash algorithm encrypt.key-secret=<str> - ID of secret providing qcow AES key or LUKS passphrase encryption=<bool (on/off)> - Encrypt the image with format 'aes'. (Deprecated in favor of encrypt.format=aes) + extent_size_hint=<size> - Extent size hint for the image file, 0 to disable lazy_refcounts=<bool (on/off)> - Postpone refcount updates nocow=<bool (on/off)> - Turn off copy-on-write (valid only on btrfs) preallocation=<str> - Preallocation mode (allowed values: off, metadata, falloc, full) @@ -134,6 +137,7 @@ Supported options: encrypt.ivgen-hash-alg=<str> - Name of IV generator hash algorithm encrypt.key-secret=<str> - ID of secret providing qcow AES key or LUKS passphrase encryption=<bool (on/off)> - Encrypt the image with format 'aes'. (Deprecated in favor of encrypt.format=aes) + extent_size_hint=<size> - Extent size hint for the image file, 0 to disable lazy_refcounts=<bool (on/off)> - Postpone refcount updates nocow=<bool (on/off)> - Turn off copy-on-write (valid only on btrfs) preallocation=<str> - Preallocation mode (allowed values: off, metadata, falloc, full) @@ -158,6 +162,7 @@ Supported options: encrypt.ivgen-hash-alg=<str> - Name of IV generator hash algorithm encrypt.key-secret=<str> - ID of secret providing qcow AES key or LUKS passphrase encryption=<bool (on/off)> - Encrypt the image with format 'aes'. (Deprecated in favor of encrypt.format=aes) + extent_size_hint=<size> - Extent size hint for the image file, 0 to disable lazy_refcounts=<bool (on/off)> - Postpone refcount updates nocow=<bool (on/off)> - Turn off copy-on-write (valid only on btrfs) preallocation=<str> - Preallocation mode (allowed values: off, metadata, falloc, full) @@ -182,6 +187,7 @@ Supported options: encrypt.ivgen-hash-alg=<str> - Name of IV generator hash algorithm encrypt.key-secret=<str> - ID of secret providing qcow AES key or LUKS passphrase encryption=<bool (on/off)> - Encrypt the image with format 'aes'. (Deprecated in favor of encrypt.format=aes) + extent_size_hint=<size> - Extent size hint for the image file, 0 to disable lazy_refcounts=<bool (on/off)> - Postpone refcount updates nocow=<bool (on/off)> - Turn off copy-on-write (valid only on btrfs) preallocation=<str> - Preallocation mode (allowed values: off, metadata, falloc, full) @@ -206,6 +212,7 @@ Supported options: encrypt.ivgen-hash-alg=<str> - Name of IV generator hash algorithm encrypt.key-secret=<str> - ID of secret providing qcow AES key or LUKS passphrase encryption=<bool (on/off)> - Encrypt the image with format 'aes'. (Deprecated in favor of encrypt.format=aes) + extent_size_hint=<size> - Extent size hint for the image file, 0 to disable lazy_refcounts=<bool (on/off)> - Postpone refcount updates nocow=<bool (on/off)> - Turn off copy-on-write (valid only on btrfs) preallocation=<str> - Preallocation mode (allowed values: off, metadata, falloc, full) @@ -230,6 +237,7 @@ Supported options: encrypt.ivgen-hash-alg=<str> - Name of IV generator hash algorithm encrypt.key-secret=<str> - ID of secret providing qcow AES key or LUKS passphrase encryption=<bool (on/off)> - Encrypt the image with format 'aes'. (Deprecated in favor of encrypt.format=aes) + extent_size_hint=<size> - Extent size hint for the image file, 0 to disable lazy_refcounts=<bool (on/off)> - Postpone refcount updates nocow=<bool (on/off)> - Turn off copy-on-write (valid only on btrfs) preallocation=<str> - Preallocation mode (allowed values: off, metadata, falloc, full) @@ -353,6 +361,7 @@ Supported options: encrypt.ivgen-hash-alg=<str> - Name of IV generator hash algorithm encrypt.key-secret=<str> - ID of secret providing qcow AES key or LUKS passphrase encryption=<bool (on/off)> - Encrypt the image with format 'aes'. (Deprecated in favor of encrypt.format=aes) + extent_size_hint=<size> - Extent size hint for the image file, 0 to disable lazy_refcounts=<bool (on/off)> - Postpone refcount updates nocow=<bool (on/off)> - Turn off copy-on-write (valid only on btrfs) preallocation=<str> - Preallocation mode (allowed values: off, metadata, falloc, full) @@ -377,6 +386,7 @@ Supported options: encrypt.ivgen-hash-alg=<str> - Name of IV generator hash algorithm encrypt.key-secret=<str> - ID of secret providing qcow AES key or LUKS passphrase encryption=<bool (on/off)> - Encrypt the image with format 'aes'. (Deprecated in favor of encrypt.format=aes) + extent_size_hint=<size> - Extent size hint for the image file, 0 to disable lazy_refcounts=<bool (on/off)> - Postpone refcount updates nocow=<bool (on/off)> - Turn off copy-on-write (valid only on btrfs) preallocation=<str> - Preallocation mode (allowed values: off, metadata, falloc, full) @@ -401,6 +411,7 @@ Supported options: encrypt.ivgen-hash-alg=<str> - Name of IV generator hash algorithm encrypt.key-secret=<str> - ID of secret providing qcow AES key or LUKS passphrase encryption=<bool (on/off)> - Encrypt the image with format 'aes'. (Deprecated in favor of encrypt.format=aes) + extent_size_hint=<size> - Extent size hint for the image file, 0 to disable lazy_refcounts=<bool (on/off)> - Postpone refcount updates nocow=<bool (on/off)> - Turn off copy-on-write (valid only on btrfs) preallocation=<str> - Preallocation mode (allowed values: off, metadata, falloc, full) @@ -425,6 +436,7 @@ Supported options: encrypt.ivgen-hash-alg=<str> - Name of IV generator hash algorithm encrypt.key-secret=<str> - ID of secret providing qcow AES key or LUKS passphrase encryption=<bool (on/off)> - Encrypt the image with format 'aes'. (Deprecated in favor of encrypt.format=aes) + extent_size_hint=<size> - Extent size hint for the image file, 0 to disable lazy_refcounts=<bool (on/off)> - Postpone refcount updates nocow=<bool (on/off)> - Turn off copy-on-write (valid only on btrfs) preallocation=<str> - Preallocation mode (allowed values: off, metadata, falloc, full) @@ -449,6 +461,7 @@ Supported options: encrypt.ivgen-hash-alg=<str> - Name of IV generator hash algorithm encrypt.key-secret=<str> - ID of secret providing qcow AES key or LUKS passphrase encryption=<bool (on/off)> - Encrypt the image with format 'aes'. (Deprecated in favor of encrypt.format=aes) + extent_size_hint=<size> - Extent size hint for the image file, 0 to disable lazy_refcounts=<bool (on/off)> - Postpone refcount updates nocow=<bool (on/off)> - Turn off copy-on-write (valid only on btrfs) preallocation=<str> - Preallocation mode (allowed values: off, metadata, falloc, full) @@ -473,6 +486,7 @@ Supported options: encrypt.ivgen-hash-alg=<str> - Name of IV generator hash algorithm encrypt.key-secret=<str> - ID of secret providing qcow AES key or LUKS passphrase encryption=<bool (on/off)> - Encrypt the image with format 'aes'. (Deprecated in favor of encrypt.format=aes) + extent_size_hint=<size> - Extent size hint for the image file, 0 to disable lazy_refcounts=<bool (on/off)> - Postpone refcount updates nocow=<bool (on/off)> - Turn off copy-on-write (valid only on btrfs) preallocation=<str> - Preallocation mode (allowed values: off, metadata, falloc, full) @@ -497,6 +511,7 @@ Supported options: encrypt.ivgen-hash-alg=<str> - Name of IV generator hash algorithm encrypt.key-secret=<str> - ID of secret providing qcow AES key or LUKS passphrase encryption=<bool (on/off)> - Encrypt the image with format 'aes'. (Deprecated in favor of encrypt.format=aes) + extent_size_hint=<size> - Extent size hint for the image file, 0 to disable lazy_refcounts=<bool (on/off)> - Postpone refcount updates nocow=<bool (on/off)> - Turn off copy-on-write (valid only on btrfs) preallocation=<str> - Preallocation mode (allowed values: off, metadata, falloc, full) @@ -521,6 +536,7 @@ Supported options: encrypt.ivgen-hash-alg=<str> - Name of IV generator hash algorithm encrypt.key-secret=<str> - ID of secret providing qcow AES key or LUKS passphrase encryption=<bool (on/off)> - Encrypt the image with format 'aes'. (Deprecated in favor of encrypt.format=aes) + extent_size_hint=<size> - Extent size hint for the image file, 0 to disable lazy_refcounts=<bool (on/off)> - Postpone refcount updates nocow=<bool (on/off)> - Turn off copy-on-write (valid only on btrfs) preallocation=<str> - Preallocation mode (allowed values: off, metadata, falloc, full) diff --git a/tests/qemu-iotests/243 b/tests/qemu-iotests/243 index a61852f6d9..17388a4644 100755 --- a/tests/qemu-iotests/243 +++ b/tests/qemu-iotests/243 @@ -51,7 +51,7 @@ for mode in off metadata falloc full; do echo "=== preallocation=$mode ===" echo - _make_test_img -o "preallocation=$mode" 64M + _make_test_img -o "preallocation=$mode,extent_size_hint=0" 64M printf "File size: " du -b $TEST_IMG | cut -f1 @@ -68,7 +68,8 @@ for mode in off metadata falloc full; do echo "=== External data file: preallocation=$mode ===" echo - _make_test_img -o "data_file=$TEST_IMG.data,preallocation=$mode" 64M + _make_test_img \ + -o "data_file=$TEST_IMG.data,preallocation=$mode,extent_size_hint=0" 64M echo -n "qcow2 file size: " du -b $TEST_IMG | cut -f1 @@ -79,7 +80,7 @@ for mode in off metadata falloc full; do echo -n "qcow2 disk usage: " [ $(du -B1 $TEST_IMG | cut -f1) -lt 1048576 ] && echo "low" || echo "high" echo -n "data disk usage: " - [ $(du -B1 $TEST_IMG.data | cut -f1) -lt 1048576 ] && echo "low" || echo "high" + [ $(du -B1 $TEST_IMG.data | cut -f1) -lt 2097152 ] && echo "low" || echo "high" done diff --git a/tests/qemu-iotests/243.out b/tests/qemu-iotests/243.out index dcb33fac32..8bd3d79d66 100644 --- a/tests/qemu-iotests/243.out +++ b/tests/qemu-iotests/243.out @@ -2,31 +2,31 @@ QA output created by 243 === preallocation=off === -Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=67108864 preallocation=off +Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=67108864 preallocation=off extent_size_hint=0 File size: 196616 Disk usage: low === preallocation=metadata === -Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=67108864 preallocation=metadata +Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=67108864 preallocation=metadata extent_size_hint=0 File size: 67436544 Disk usage: low === preallocation=falloc === -Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=67108864 preallocation=falloc +Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=67108864 preallocation=falloc extent_size_hint=0 File size: 67436544 Disk usage: high === preallocation=full === -Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=67108864 preallocation=full +Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=67108864 preallocation=full extent_size_hint=0 File size: 67436544 Disk usage: high === External data file: preallocation=off === -Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=67108864 data_file=TEST_DIR/t.IMGFMT.data preallocation=off +Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=67108864 data_file=TEST_DIR/t.IMGFMT.data preallocation=off extent_size_hint=0 qcow2 file size: 196616 data file size: 67108864 qcow2 disk usage: low @@ -34,7 +34,7 @@ data disk usage: low === External data file: preallocation=metadata === -Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=67108864 data_file=TEST_DIR/t.IMGFMT.data preallocation=metadata +Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=67108864 data_file=TEST_DIR/t.IMGFMT.data preallocation=metadata extent_size_hint=0 qcow2 file size: 327680 data file size: 67108864 qcow2 disk usage: low @@ -42,7 +42,7 @@ data disk usage: low === External data file: preallocation=falloc === -Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=67108864 data_file=TEST_DIR/t.IMGFMT.data preallocation=falloc +Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=67108864 data_file=TEST_DIR/t.IMGFMT.data preallocation=falloc extent_size_hint=0 qcow2 file size: 327680 data file size: 67108864 qcow2 disk usage: low @@ -50,7 +50,7 @@ data disk usage: high === External data file: preallocation=full === -Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=67108864 data_file=TEST_DIR/t.IMGFMT.data preallocation=full +Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=67108864 data_file=TEST_DIR/t.IMGFMT.data preallocation=full extent_size_hint=0 qcow2 file size: 327680 data file size: 67108864 qcow2 disk usage: low