Free space tree issues

[josefbacik]

• [ ] We're checking the mount option for btrfs_show_options, not btrfs_fs_compat_ro(), which means that if you mount later it shows space_cache as the mount option, not space_cache=v2, which confused the fuck out of me and made me thing something was wrong.
  • [ ] Apparently mount -o space_cache=v2 with a large enough fs will take take forever and block trying to make the free space tree, we should probably handle this asynchronously.

[cmurf]

Related: https://lore.kernel.org/linux-btrfs/20200601175252.GC18421@twin.jikos.cz/ cmurf: I was surprised there's no warning when I use space_cache=v2 without first clearing v1. knorrie: t's just sitting there, occupying some space, doing nothing. Sterba: Hm that's not ideal, right?

And also:

mount -o clear_cache apparently just invalidates v1, it doesn't actually ever remove it

mount -o clear_cache,space_cache=v2, the mount command claims it's using v2 in mount, but isn't (feature flag is not set, v2 tree is not created)

[knorrie]

As seen at https://lore.kernel.org/linux-btrfs/87ec1249-b0b8-643b-9031-ebc9aae5f80a@mendix.com/

[josefbacik]

This got resolved with Boris's patches.

[unfa]

I have a filesystem that suddenly only mounts RO. Dmesg shows this:

pią kwi 15 16:23:40 2022] BTRFS info (device sdh): flagging fs with big metadata feature
[pią kwi 15 16:23:40 2022] BTRFS info (device sdh): using free space tree
[pią kwi 15 16:23:40 2022] BTRFS info (device sdh): has skinny extents
[pią kwi 15 16:23:53 2022] BTRFS info (device sdg1): setting compat-ro feature flag for FREE_SPACE_TREE (0x1)
[pią kwi 15 16:23:53 2022] BTRFS info (device sdg1): setting compat-ro feature flag for FREE_SPACE_TREE_VALID (0x2)
[pią kwi 15 16:24:44 2022] BTRFS info (device sdg1): flagging fs with big metadata feature
[pią kwi 15 16:24:44 2022] BTRFS info (device sdg1): force clearing of disk cache
[pią kwi 15 16:24:44 2022] BTRFS info (device sdg1): force zstd compression, level 3
[pią kwi 15 16:24:44 2022] BTRFS info (device sdg1): using free space tree
[pią kwi 15 16:24:44 2022] BTRFS info (device sdg1): has skinny extents
[pią kwi 15 16:24:54 2022] BTRFS info (device sdg1): clearing free space tree
[pią kwi 15 16:24:54 2022] BTRFS info (device sdg1): clearing compat-ro feature flag for FREE_SPACE_TREE (0x1)
[pią kwi 15 16:24:54 2022] BTRFS info (device sdg1): clearing compat-ro feature flag for FREE_SPACE_TREE_VALID (0x2)
[pią kwi 15 16:24:56 2022] BTRFS info (device sdg1): creating free space tree
[pią kwi 15 16:25:39 2022] BTRFS info (device sdg1): setting compat-ro feature flag for FREE_SPACE_TREE (0x1)
[pią kwi 15 16:25:39 2022] BTRFS info (device sdg1): setting compat-ro feature flag for FREE_SPACE_TREE_VALID (0x2)

How can I mount this FS in read-write?