Control: tags -1 + moreinfo Hi James,
On Tue, Sep 23, 2025 at 08:04:25PM +0200, James Young wrote: > Package: src:linux > Version: 6.1.129-1 > Severity: normal > X-Debbugs-Cc: [email protected] > > Dear Maintainer, > > > * What led up to the situation? > We made empty files in a loop, in parallel, under CPU and I/O load. > We had an outer Btrfs image file with compression, which contained a Btrfs > image file, which contained billions of empty files. > We wrote around 100TB to the inner image file. > Around 60TB in, compression quietly shut off. > We ran out of space; both mounts presented i/o errors. > > * What exactly did you do (or not do) that was effective (or ineffective)? > * I unmounted the inner and outer images. > I didn't take note of memory usage before this point. > * dump debug info for the outer image - `btrfs inspect-internal dump-tree > --dfs ...` > * We started a btrfsck. (twice, actually; breadth-first hit memory limits, > I think) > After that, I learned about `btrfs check`, but didn't interrupt the btrfsck, > due to Sunk Cost Fallacy. > The btrfsck is still running. It's of extremely dubious value now. > * check the kernel logs > * I grepped for btrfs, the mount points, compress, and zstd. I didn’t find > a smoking gun in the right timeframe. > > not done yet: > * mount the outer image > * rebooted > * tried a newer kernel. we're currently on kernel 6.1.129; we could go to > newer 6.1 or 6.12 kernels > * redo live file system compression, with e.g. `btrfs filesystem defrag > -czstd` > * fstrim the outer image > > goals: > * work out what happened. > How can we help? > * help avoid it happening again, to others > * salvage what we can > > I've run `bugreport` as a non-privileged user. Let me know if root access > would give a fuller picture. I believe the best thing you could do here is to contact actually upstream people directly. get_maintainers and the MAINTAINERS file has: BTRFS FILE SYSTEM M: Chris Mason <[email protected]> M: Josef Bacik <[email protected]> M: David Sterba <[email protected]> L: [email protected] S: Maintained W: https://btrfs.readthedocs.io Q: https://patchwork.kernel.org/project/linux-btrfs/list/ C: irc://irc.libera.chat/btrfs T: git git://git.kernel.org/pub/scm/linux/kernel/git/kdave/linux.git F: Documentation/filesystems/btrfs.rst F: fs/btrfs/ F: include/linux/btrfs* F: include/trace/events/btrfs.h F: include/uapi/linux/btrfs* So I would suggest you to contact above maintainers including the list. Please keep this downstream bugreport as well in the recipients list. Regards, Salvatore
