[btrfs] support dynamic_reclaim

[motiejus]

What type of PR is this?

Uncomment only one /kind <> line, hit enter to put that in a new line, and remove leading whitespaces from that line:

/kind api-change
/kind bug
/kind cleanup
/kind design
/kind documentation
/kind failing-test

/kind feature

/kind flake

What this PR does / why we need it:

Currently btrfs offers 3 methods to balance the filesystem:

1. beginning of time: btrfs filesystem balance.
2. kernel v5.19+: /sys/fs/btrfs/UUID/allocation/{meta,}data/bg_reclaim_threshold.
3. kernel v6.11+: /sys/fs/btrfs/UUID/allocation/{meta,}data/dynamic_reclaim.

(3) is most robust out of the 3, and best documented in the kernel commit f5ff64ccf7bb7274ed66b0d835b2f6ae10af5d7a. Once GKE rolls up to the kernel v6.11, this seems to be the best/recommended option to set.

Fixes #2163

Special notes for your reviewer:

So far we have landed all btrfs-specific options we use today. However, it's quite certain we will move from bg_reclaim_threshold to dynamic_reclaim when we catch up on the kernel.

Does this PR introduce a user-facing change?: yes.

add btrfs-specific option to control [`dynamic_reclaim`](https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=f5ff64ccf7bb7274ed66b0d835b2f6ae10af5d7a).

[k8s-ci-robot]

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[mattcary]

typo "thresho"

[mattcary]

typo "thresho"

[mattcary]

Might be nice in these docs to put the values supported; eg it wasn't obvious to me that dynamic_reclaim took 0/1.

[motiejus]

@mattcary upon closer inspection I found that I got the setting names wrong in the first place!

I converted it to a table now, added value ranges and a bit of explanation for each setting.

[mattcary]

/ok-to-test

[mattcary]

/lgtm
/approve

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: mattcary, motiejus

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[k8s-ci-robot]

@motiejus: The following test failed, say /retest to rerun all failed tests or /retest-required to rerun all mandatory failed tests:

Test name	Commit	Details	Required	Rerun command
pull-gcp-compute-persistent-disk-csi-driver-e2e-arm	427e119	link	false	/test pull-gcp-compute-persistent-disk-csi-driver-e2e-arm

Full PR test history. Your PR dashboard. Please help us cut down on flakes by linking to an open issue when you hit one in your PR.

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Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the kubernetes-sigs/prow repository. I understand the commands that are listed here.