Re: [PATCH] Docs/mm/damon: document min_nr_regions constraint and rationale

[Liew Rui Yan <aethernet65535@gmail.com>]

The current DAMON implementation requires 'min_nr_regions' to be at
least 3. However, this constraint is not explicitly documented in the
admin-guide documents, nor is its design rationale explained in the
design document.

Add a section in design.rst to explain the rationale: the virtual
address space monitoring design needs to handle at least three regions
to accommodate two large unmapped areas. While this is specific to
'vaddr', DAMON currently enforces it across all operation sets for
consistency.

Also update reclaim.rst and lru_sort.rst by adding cross-references to
this constraint at the end of their respective parameter description or
usage sections, ensuring users are aware of the lower bound.

This change is motivated from a recent discussion [1].

[1] https://lore.kernel.org/damon/20260319151528.86490-1-sj@kernel.org/T/#t