On 30.11.18 16:24, Vladimir Sementsov-Ogievskiy wrote: > 30.11.2018 17:59, Max Reitz wrote: >> On 30.11.18 15:51, Vladimir Sementsov-Ogievskiy wrote: >>> 30.11.2018 17:10, Kevin Wolf wrote: >>>> Am 30.11.2018 um 14:48 hat Vladimir Sementsov-Ogievskiy geschrieben: >>>>> 30.11.2018 16:13, Max Reitz wrote: >>>>>> On 30.11.18 14:06, Vladimir Sementsov-Ogievskiy wrote: >>>>>>> 30.11.2018 15:30, Max Reitz wrote: >>>>>>>> On 29.11.18 11:18, Vladimir Sementsov-Ogievskiy wrote: >>>>>>>>> This test is broken without previous commit fixing dead-lock in >>>>>>>>> mirror. >>>>>>>>> >>>>>>>>> Signed-off-by: Vladimir Sementsov-Ogievskiy<vsement...@virtuozzo.com> >>>>>>>>> --- >>>>>>>>> tests/qemu-iotests/235 | 59 >>>>>>>>> ++++++++++++++++++++++++++++++++++++++ >>>>>>>>> tests/qemu-iotests/235.out | 1 + >>>>>>>>> tests/qemu-iotests/group | 1 + >>>>>>>>> 3 files changed, 61 insertions(+) >>>>>>>>> create mode 100755 tests/qemu-iotests/235 >>>>>>>>> create mode 100644 tests/qemu-iotests/235.out >>>>>>>> I'll get to the first patch in a second, but first a suggestion for >>>>>>>> this >>>>>>>> patch: I think it's not so good to use 2 GB of space for a test (1 GB >>>>>>>> for the source, 1 GB for the target). So I tried my luck and found >>>>>>>> that >>>>>>>> the test works, too, if you just use preallocation=metadata for the >>>>>>>> source (instead of actually writing data) and blockdev-mirror'ing the >>>>>>>> data to a throttled null-co device. >>>>>>> >>>>>>> Hmm, so parsing metadata is enough for qcow2 to yield on write, yes? >>>>>> >>>>>> Apparently so. If you can confirm that applying those changes to the >>>>>> test still make it work (i.e., fail before patch 1, pass afterwards), >>>>>> then I think it is just as good. >>>>> >>>>> Ok, I've checked that your changes works for me. >>>>> >>>>> hm, but we write to null, so, yield on write comes from throttling, >>>>> however, >>>>> without preallocation=metadata, it don't work.., do you know, why we need >>>>> preallocation to reproduce? >>>> >>>> If I should take a guess, probably because mirror only copies allocated >>>> clusters? >>>> >>>> Kevin >>>> >>> >>> hm, so, what preallocation=metadata does? I thought, it preallocates >>> tables, but all qcow2 clusters would be unallocated.. >> >> No, it initializes all metadata structures (i.e., L2 tables) so they >> point to data clusters; which is why you cannot use it with backing >> files. It's just that the data clusters are not written. > > so, clusters are allocated? in this case, we don't avoid allocating of 1G, > but only have a performance gain?
The data isn't written, so less than 1 MB are actually allocated on-disk. The L2 tables do point to offsets over a range of 1 GB, but they should all be holes on the filesystem. Max
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