In bcachefs, is creating a reflink O(n) in the size of the file, or in
the number of currently unshared extents that need to be moved into the
reflink btree?  The former would be annoying, but the latter is
proportional to the number of modifications to the file since it was
last reflinked, which is fine for my use-case so long as unlinking a
heavily reflinked file is also fast.  My reading of “bcachefs:
Principles of Operation” suggests the latter.

Basically, if a file is already reflinked, is reflinking it *again*
cheap?
-- 
Sincerely,
Demi Marie Obenour (she/her/hers)
Invisible Things Lab