Re: [PATCH for-5.1] file-posix: Mitigate file fragmentation with extent size hints
Am 13.07.2020 um 15:12 hat Kevin Wolf geschrieben: > Am 13.07.2020 um 11:08 hat Max Reitz geschrieben: > > On 10.07.20 18:12, Max Reitz wrote: > > > 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=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 100 > > >>> -S 8192 -o 0 > > >>> Sending 100 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 100 > > >>> -S 8192 -o 4096 > > >>> Sending 100 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: 200 extents found > > >>> $ time ./qemu-img map ~/tmp/test.raw > > >>> Offset Length Mapped to File > > >>> 0 0x1e848 0 > > >>> /home/kwolf/tmp/test.raw > > >>> > > >>> real0m1,279s > > >>> user0m0,043s > > >>> 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 100 > > >>> -S 8192 -o 0 > > >>> Sending 100 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 100 > > >>> -S 8192 -o 4096 > > >>> Sending 100 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 0x1e848 0 > > >>> /home/kwolf/tmp/test.raw > > >>> > > >>> real0m0,061s > > >>> user0m0,040s > > >>> sys 0m0,014s > > >>> > > >>> Signed-off-by: Kevin Wolf > > >> > > >> 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’t work there). I suppose the same may be true > > > on other filesystems as well. Should it be filtered out? > > I guess we just shouldn't print a warning if the requested hint is 0. > > > This patch also breaks 059, 106, and 175. > > Hm, I was sure I had tested raw... Anyway, 059 should filter out the > actual size (how could this ever work?), and 175 is obvious, too - it > tries to be clever, but not clever enough. > > 106 is a
Re: [PATCH for-5.1] file-posix: Mitigate file fragmentation with extent size hints
Am 13.07.2020 um 11:08 hat Max Reitz geschrieben: > On 10.07.20 18:12, Max Reitz wrote: > > 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=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 100 -S > >>> 8192 -o 0 > >>> Sending 100 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 100 -S > >>> 8192 -o 4096 > >>> Sending 100 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: 200 extents found > >>> $ time ./qemu-img map ~/tmp/test.raw > >>> Offset Length Mapped to File > >>> 0 0x1e848 0 > >>> /home/kwolf/tmp/test.raw > >>> > >>> real0m1,279s > >>> user0m0,043s > >>> 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 100 -S > >>> 8192 -o 0 > >>> Sending 100 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 100 -S > >>> 8192 -o 4096 > >>> Sending 100 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 0x1e848 0 > >>> /home/kwolf/tmp/test.raw > >>> > >>> real0m0,061s > >>> user0m0,040s > >>> sys 0m0,014s > >>> > >>> Signed-off-by: Kevin Wolf > >> > >> 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’t work there). I suppose the same may be true > > on other filesystems as well. Should it be filtered out? I guess we just shouldn't print a warning if the requested hint is 0. > This patch also breaks 059, 106, and 175. Hm, I was sure I had tested raw... Anyway, 059 should filter out the actual size (how could this ever work?), and 175 is obvious, too - it tries to be clever, but not clever enough. 106 is a bit mysterious because the error message implies that the images end up smaller than before, which shouldn't be the case. I'll have a look. Kevin signature.asc Description: PGP signature
Re: [PATCH for-5.1] file-posix: Mitigate file fragmentation with extent size hints
On 10.07.20 18:12, Max Reitz wrote: > 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=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 100 -S >>> 8192 -o 0 >>> Sending 100 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 100 -S >>> 8192 -o 4096 >>> Sending 100 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: 200 extents found >>> $ time ./qemu-img map ~/tmp/test.raw >>> Offset Length Mapped to File >>> 0 0x1e848 0 /home/kwolf/tmp/test.raw >>> >>> real0m1,279s >>> user0m0,043s >>> 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 100 -S >>> 8192 -o 0 >>> Sending 100 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 100 -S >>> 8192 -o 4096 >>> Sending 100 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 0x1e848 0 /home/kwolf/tmp/test.raw >>> >>> real0m0,061s >>> user0m0,040s >>> sys 0m0,014s >>> >>> Signed-off-by: Kevin Wolf >> >> 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’t work there). I suppose the same may be true > on other filesystems as well. Should it be filtered out? This patch also breaks 059, 106, and 175. Max signature.asc Description: OpenPGP digital signature
Re: [PATCH for-5.1] file-posix: Mitigate file fragmentation with extent size hints
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=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 100 -S >> 8192 -o 0 >> Sending 100 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 100 -S >> 8192 -o 4096 >> Sending 100 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: 200 extents found >> $ time ./qemu-img map ~/tmp/test.raw >> Offset Length Mapped to File >> 0 0x1e848 0 /home/kwolf/tmp/test.raw >> >> real0m1,279s >> user0m0,043s >> 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 100 -S >> 8192 -o 0 >> Sending 100 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 100 -S >> 8192 -o 4096 >> Sending 100 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 0x1e848 0 /home/kwolf/tmp/test.raw >> >> real0m0,061s >> user0m0,040s >> sys 0m0,014s >> >> Signed-off-by: Kevin Wolf > > 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’t work there). I suppose the same may be true on other filesystems as well. Should it be filtered out? Max signature.asc Description: OpenPGP digital signature
Re: [PATCH for-5.1] file-posix: Mitigate file fragmentation with extent size hints
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 100 -S 8192 > -o 0 > Sending 100 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 100 -S 8192 > -o 4096 > Sending 100 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: 200 extents found > $ time ./qemu-img map ~/tmp/test.raw > Offset Length Mapped to File > 0 0x1e848 0 /home/kwolf/tmp/test.raw > > real0m1,279s > user0m0,043s > 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 100 -S 8192 > -o 0 > Sending 100 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 100 -S 8192 > -o 4096 > Sending 100 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 0x1e848 0 /home/kwolf/tmp/test.raw > > real0m0,061s > user0m0,040s > sys 0m0,014s > > Signed-off-by: Kevin Wolf 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= - Name of IV generator hash algorithm encrypt.key-secret= - ID of secret providing qcow AES key or LUKS passphrase encryption= - Encrypt the image with format 'aes'. (Deprecated in favor of encrypt.format=aes) + extent_size_hint= - Extent size hint for the image file, 0 to disable lazy_refcounts= - Postpone refcount updates nocow= - Turn off copy-on-write (valid only on btrfs) preallocation=- Preallocation mode (allowed values: off, metadata, falloc, full) @@ -86,6 +87,7 @@ Supported options: encrypt.ivgen-hash-alg= - Name of IV generator hash algorithm encrypt.key-secret= - ID of secret providing qcow AES key or LUKS passphrase encryption= - Encrypt the image with format 'aes'. (Deprecated in favor of encrypt.format=aes) + extent_size_hint= - Extent size hint for the image file, 0 to disable lazy_refcounts= - Postpone refcount updates nocow= - Turn off copy-on-write (valid only on btrfs) preallocation=- Preallocation mode (allowed values:
Re: [PATCH for-5.1] file-posix: Mitigate file fragmentation with extent size hints
On 7/7/20 9:23 AM, Kevin Wolf wrote:
Espeically when O_DIRECT is used with image files so that the page cache
Especially
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.
Cool!
Signed-off-by: Kevin Wolf
---
qapi/block-core.json | 11 ++
include/block/block_int.h | 1 +
block/file-posix.c| 42 +++
3 files changed, 50 insertions(+), 4 deletions(-)
+#ifdef FS_IOC_FSSETXATTR
+/*
+ * Try to set the extent size hint. Failure is not fatal, and a warning is
+ * only printed if the option was explicitly specified.
+ */
+{
+struct fsxattr attr;
+result = ioctl(fd, FS_IOC_FSGETXATTR, );
+if (result == 0) {
+attr.fsx_xflags |= FS_XFLAG_EXTSIZE;
+attr.fsx_extsize = file_opts->extent_size_hint;
+result = ioctl(fd, FS_IOC_FSSETXATTR, );
+}
+if (result < 0 && file_opts->has_extent_size_hint) {
+warn_report("Failed to set extent size hint: %s",
+strerror(errno));
+}
+}
+#endif
That's a neat ioctl to learn.
Reviewed-by: Eric Blake
--
Eric Blake, Principal Software Engineer
Red Hat, Inc. +1-919-301-3226
Virtualization: qemu.org | libvirt.org
[PATCH for-5.1] file-posix: Mitigate file fragmentation with extent size hints
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 100 -S 8192
-o 0
Sending 100 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 100 -S 8192
-o 4096
Sending 100 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: 200 extents found
$ time ./qemu-img map ~/tmp/test.raw
Offset Length Mapped to File
0 0x1e848 0 /home/kwolf/tmp/test.raw
real0m1,279s
user0m0,043s
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 100 -S 8192
-o 0
Sending 100 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 100 -S 8192
-o 4096
Sending 100 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 0x1e848 0 /home/kwolf/tmp/test.raw
real0m0,061s
user0m0,040s
sys 0m0,014s
Signed-off-by: Kevin Wolf
---
qapi/block-core.json | 11 ++
include/block/block_int.h | 1 +
block/file-posix.c| 42 +++
3 files changed, 50 insertions(+), 4 deletions(-)
diff --git a/qapi/block-core.json b/qapi/block-core.json
index 0e1c6a59f2..ddd3737d90 100644
--- a/qapi/block-core.json
+++ b/qapi/block-core.json
@@ -4185,14 +4185,17 @@
# falloc (if defined CONFIG_POSIX_FALLOCATE),
# full (if defined CONFIG_POSIX))
# @nocow: Turn off copy-on-write (valid only on btrfs; default: off)
+# @extent-size-hint: Extent size hint to add to the image file; 0 for not
+#adding an extent size hint (default: 1 MB, since 5.1)
#
# Since: 2.12
##
{ 'struct': 'BlockdevCreateOptionsFile',
- 'data': { 'filename': 'str',
-'size': 'size',
-'*preallocation': 'PreallocMode',
-'*nocow': 'bool' } }
+ 'data': { 'filename': 'str',
+'size': 'size',
+'*preallocation': 'PreallocMode',
+'*nocow': 'bool',
+'*extent-size-hint':'size'} }
##
# @BlockdevCreateOptionsGluster:
diff --git a/include/block/block_int.h b/include/block/block_int.h
index 791de6a59c..03cd266948 100644
--- a/include/block/block_int.h
+++ b/include/block/block_int.h
@@ -53,6 +53,7 @@
#define BLOCK_OPT_ADAPTER_TYPE "adapter_type"
#define BLOCK_OPT_REDUNDANCY"redundancy"
#define BLOCK_OPT_NOCOW
