Re: bcachefs dropped writes with lockless buffered io path, COMPACTION/MIGRATION=y

[clonejo <clonejo@shakik.de>]

On 27/08/2024 05:29, Kent Overstreet wrote:
> Interestingly, it only triggers for QEMU - the test fails pretty
> consistently and we have a lot of nixos users, we'd notice (via nix
> store verifies) if the corruption was more widespread. We believe it
> only triggers with QEMU's snapshots mode (but don't quote me on that).

I have had this with 6.10.6 #1-NixOS (with nocow_lock patch added) _on 
bare hardware_, no qemu involved.

So far, i have seen it only on files in /var/lib/nixos, similar to 
https://github.com/NixOS/nixpkgs/issues/126971.

nix-store --verify --check-contents is still running, but no errors yet.

Also, copygc and rebalance block suspends for me, though the fs gets 
unmounted fine on shutdown.

Mount options:
> /dev/nvme0n1p2:/dev/sdc3:/dev/sdd2:/dev/sde3:/dev/sdb3:/dev/sda3 on / type bcachefs (rw,relatime,metadata_replicas=2,data_replicas=2,background_compression=zstd,metadata_target=ssd,foreground_target=ssd.tlc,background_target=hdd,promote_target=ssd)