convert kernel settings to a table, patch up a few things.

Author: motiejus

README.md

@@ -100,11 +100,12 @@ As noted in [GCP PD documentation](https://cloud.google.com/kubernetes-engine/do
 
 `btrfs` filesystem accepts the following "special" mount options and the sysfs paths they target:
 
-- `btrfs-data-bg_reclaim_threshold`: `/sys/fs/btrfs/FS-UUID/allocation/data/bg_reclaim_threshold`. Supported on Linux v5.19+.
-- `btrfs-metadata-bg_reclaim_thresho: `/sys/fs/btrfs/FS-UUID/allocation/metadata/bg_reclaim_threshold`. Supported on Linux v5.19+.
-- `btrfs-data-dynamic_reclaim`: `/sys/fs/btrfs/FS-UUID/allocation/data/dynamic_reclaim`. Supported on Linux v6.11+.
-- `btrfs-metadata-bg_reclaim_thresho: `/sys/fs/btrfs/FS-UUID/allocation/metadata/bg_reclaim_threshold`. Supported on Linux v6.11+.
-- `btrfs-bdi-read_ahead_kb`: `/sys/fs/btrfs/FS-UUID/bdi/read_ahead_kb`.
+| Setting                                          | Sysfs path                                                        | Value          | Default                 | Supported on | Notes |
+|--------------------------------------------------|-------------------------------------------------------------------|----------------|-------------------------|----------------------------------------------|-------|
+| `btrfs-allocation-data-bg_reclaim_threshold`     | `/sys/fs/btrfs/FS-UUID/allocation/data/bg_reclaim_threshold`      | 0–99 (percent) | 0 (disabled)            | Linux v5.19+ | Triggers background reclaim for DATA block groups when usage drops to the threshold. |
+| `btrfs-allocation-metadata-bg_reclaim_threshold` | `/sys/fs/btrfs/FS-UUID/allocation/metadata/bg_reclaim_threshold`  | 0–99 (percent) | 0 (disabled)            | Linux v5.19+ | Same as above, for METADATA block groups. |
+| `btrfs-allocation-data-dynamic_reclaim`          | `/sys/fs/btrfs/FS-UUID/allocation/data/dynamic_reclaim`           | `0` or `1`     | 0 (off)                 | Linux v6.11+ | Heuristic reclaim that addresses [some concerns](https://web.git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=f5ff64ccf7bb7274ed66b0d835b2f6ae10af5d7a) of `bg_reclaim_threshold`. |
+| `btrfs-bdi-read_ahead_kb`                        | `/sys/fs/btrfs/FS-UUID/bdi/read_ahead_kb`                         | integer kB ≥ 0 | kernel/device dependent | Linux v5.9+  | Per-BDI readahead. Powers of two are commonly used. |
 
 See more in the [in btrfs docs](https://btrfs.readthedocs.io/en/latest/ch-sysfs.html#uuid-allocations-data-metadata-system).