UPSTREAM: mm: multi-gen LRU: section for working set protection

Patch series "mm: multi-gen LRU: improve".

This patch series improves a few MGLRU functions, collects related
functions, and adds additional documentation.

This patch (of 7):

Add a section for working set protection in the code and the design doc.
The admin doc already contains its usage.

Link: https://lkml.kernel.org/r/20230118001827.1040870-1-talumbau@google.com
Link: https://lkml.kernel.org/r/20230118001827.1040870-2-talumbau@google.com


Change-Id: I65599075fd42951db7739a2ab7cee78516e157b3
Signed-off-by: T.J. Alumbaugh <talumbau@google.com>
Cc: Yu Zhao <yuzhao@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
(cherry picked from commit 7b8144e6)
Bug: 274865848
Signed-off-by: T.J. Mercier <tjmercier@google.com>