On Wed, Jul 18, 2018 at 12:01 PM, Austin S. Hemmelgarn <ahferro...@gmail.com> wrote: > On 2018-07-18 13:40, Chris Murphy wrote: >> >> On Wed, Jul 18, 2018 at 11:14 AM, Chris Murphy <li...@colorremedies.com> >> wrote: >> >>> I don't know for sure, but based on the addresses reported before and >>> after dd for the fallocated tmp file, it looks like Btrfs is not using >>> the originally fallocated addresses for dd. So maybe it is COWing into >>> new blocks, but is just as quickly deallocating the fallocated blocks >>> as it goes, and hence doesn't end up in enospc? >> >> >> Previous thread is "Problem with file system" from August 2017. And >> there's these reproduce steps from Austin which have fallocate coming >> after the dd. >> >> truncate --size=4G ./test-fs >> mkfs.btrfs ./test-fs >> mkdir ./test >> mount -t auto ./test-fs ./test >> dd if=/dev/zero of=./test/test bs=65536 count=32768 >> fallocate -l 2147483650 ./test/test && echo "Success!" >> >> >> My test Btrfs is 2G not 4G, so I'm cutting the values of dd and >> fallocate in half. >> >> [chris@f28s btrfs]$ sudo dd if=/dev/zero of=tmp bs=1M count=1000 >> 1000+0 records in >> 1000+0 records out >> 1048576000 bytes (1.0 GB, 1000 MiB) copied, 7.13391 s, 147 MB/s >> [chris@f28s btrfs]$ sync >> [chris@f28s btrfs]$ df -h >> Filesystem Size Used Avail Use% Mounted on >> /dev/mapper/vg-btrfstest 2.0G 1018M 1.1G 50% /mnt/btrfs >> [chris@f28s btrfs]$ sudo fallocate -l 1000m tmp >> >> >> Succeeds. If I do it with a 1200M file for dd and fallocate 1200M over >> it, this fails, but I kinda expect that because there's only 1.1G free >> space. But maybe that's what you're saying is the bug, it shouldn't >> fail? > > Yes, you're right, I had things backwards (well, kind of, this does work on > ext4 and regular XFS, so it arguably should work here).
I guess I'm confused what it even means to fallocate over a file with in-use blocks unless either -d or -p options are used. And from the man page, I don't grok the distinction between -d and -p either. But based on their descriptions I'd expect they both should work without enospc. -- Chris Murphy -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
