On Thu, Apr 25, 2019 at 3:28 PM Qu Wenruo <quwenruo.bt...@gmx.com> wrote: > > > > On 2019/4/25 下午10:09, Josef Bacik wrote: > > On Thu, Apr 25, 2019 at 09:50:25PM +0800, Qu Wenruo wrote: > >> > >> > >> On 2019/4/25 下午9:25, Josef Bacik wrote: > >> [snip] > >>>>> > >>>>> What if the commit is reverted, if the problem is otherwise hard to fix? > >>>>> This seems to break the semantics of fallocate so the performance should > >>>>> not the main concern here. > >>>> > >>> > >>> Are we sure the ENOSPC is coming from the data reservation? That change > >>> makes > >>> us fall back on the old behavior, which means we should still succeed at > >>> making > >>> the data reservation. > >>> > >>> However it fallocate() _does not_ guarantee you won't fail the metadata > >>> reservation, I suspect that may be what you are running into. > >> > >> For this script, we only needs 4 file extents at most. > >> Even the initial 8M metadata should be pretty enough, thus I don't think > >> it's metadata causing the problem. > >> --- > >> #!/bin/bash > >> > >> dev=/dev/test/test > >> mnt=/mnt/btrfs > >> > >> mkfs.btrfs -f $dev -b 512M > >> > >> mount $dev $mnt > >> > >> fallocate -l 384M $mnt/file1 > >> echo "fallocate success" > >> sync > >> dd if=/dev/zero bs=512K oflag=direct conv=notrunc count=768 of=$mnt/file2 > >> > > > > Wellll we don't do the nocow check _at all_ for O_DIRECT, so mystery solved > > there. > > Oh, wrong flag, remove that oflag and we still get the same problem. > > fallocate success > dd: error writing '/mnt/btrfs/file2': No space left on device
I don't get it. Why is this unexpected error? You created a fs with 512Mb, fallocated 384Mb for a file named file1, and then tried to write 384Mb 512K * 768 to a file named file2 (i.e. a different file). Wasn't the test supposed to write to file1 instead? > 95+0 records in > 94+0 records out > 49283072 bytes (49 MB, 47 MiB) copied, 0.0807034 s, 611 MB/s > > Thanks, > Qu > > > > > Josef > > > -- Filipe David Manana, “Whether you think you can, or you think you can't — you're right.”
