Refactor dirty page tracking

[ValentaTomas]

[!NOTE] Replaces dirty page tracking with a thread-safe Tracker and updates UFFD, sandbox, and build components to use it, adding unregister support and minor API changes.

• Block / Tracking:
  • Introduce block.Tracker (thread-safe bitset) with Has, Add, Reset, Offsets, BitSet, Clone; unit tests added.
  • Extend Slicer with BlockSize().
• UFFD:
  • Change constructor to uffd.New(memfile, socketPath); remove TrackedSliceDevice usage.
  • MemoryBackend API: Disable(ctx) now returns *block.Tracker.
  • Implement unregister via UFFDIO_UNREGISTER; Uffd.Disable unregisters then returns Tracker from Dirty().
  • Track faults via block.Tracker with bounded concurrency; expose offsets iterator in cross-process tests.
  • Buffer Ready() channel.
• Sandbox Integration:
  • On pause, call s.memory.Disable(ctx) and pass dirty.BitSet() to MemoryDiffCreator.
  • serveMemory updated for new UFFD constructor.
• Build / Diff:
  • Add BlockSize() to NoDiff, localDiff, and StorageDiff.
• Utils:
  • Add utils.TransformTo iterator helper.

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[ValentaTomas]

I want to do a few more end to end tests, but it should be ready to merge right after https://github.com/e2b-dev/infra/tree/uffd-refactor

[ValentaTomas]

@codex review

[ValentaTomas]

💡 Codex Review

https://github.com/e2b-dev/infra/blob/116062b7729f46356f334abb7c158dea50876bfd/packages/orchestrator/internal/sandbox/uffd/userfaultfd/serve.go#L109-L113

Handle UFFD remove events after unregister The new Disable(ctx) issues UFFDIO_UNREGISTER, which causes the kernel to emit UFFD_EVENT_REMOVE notifications on the userfaultfd. The serve loop still treats every non‑UFFD_EVENT_PAGEFAULT as an error and immediately returns ErrUnexpectedEventType. After disabling memory this will report a failure, tear down the goroutine and mark the backend as errored even though the event is expected. The loop should explicitly ignore or handle UFFD_EVENT_REMOVE (and possibly other control events) once unregistering is supported.

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Isn't UFFD_EVENT_REMOVE triggered by MADV_DONTNEED/MADV_REMOVE, which are not actually part of the UFFD unregister signalization—they are part of the UFFD memory management which we are not using. Not 100% sure though.

[chatgpt-codex-connector[bot]]

Summary

• Added the UFFD_EVENT_REMOVE constant, struct alias, and helper to surface remove event ranges for logging. packages/orchestrator/internal/sandbox/uffd/userfaultfd/constants.goL23-L112
• Updated the userfaultfd serve loop to ignore UFFD_EVENT_REMOVE notifications emitted after unregister, avoiding erroneous error handling. packages/orchestrator/internal/sandbox/uffd/userfaultfd/serve.goL109-L159

Testing

• ⚠️ go test ./packages/orchestrator/internal/sandbox/uffd/... (fails: go: command not found)

View task →

[ValentaTomas]

I'll do some last end-to-end testing and then we should be able to merge.