Summary
Checkpoint cleanup skips the on-disk obsolete pages with overflow items. Those obsolete pages are never freed until they are accessed again.

Motivation
No. Overflow items are used rarely in MongoDB, but possible that they are used by the WT standalone users.

• How likely is it that this use case or problem will occur?
  Edge case scenario of overflow items.

• If the problem does occur, what are the consequences and how severe are they?
  Disk space use increases.

• Is this issue urgent?
  No.

Acceptance Criteria (Definition of Done)
Checkpoint cleanup can able to free the obsolete pages with overflow items.

• Testing
  Functional testing is required to verify that checkpoint cleanup removes obsolete pages with overflow items.

• Documentation update
  NA

[Optional] Suggested Solution
Read the obsolete pages back into memory and mark them dirty to let the reconciliation remove the overflow items. Page read is a costly operation, limit the number of pages that are read per checkpoint.