UPSTREAM: mm: multi-gen LRU: section for rmap/PT walk feedback

Add a section for lru_gen_look_around() in the code and the design doc.

Link: https://lkml.kernel.org/r/20230118001827.1040870-3-talumbau@google.com


Change-Id: I5097af63f61b3b69ec2abee6cdbdc33c296df213
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 db19a43d)
Bug: 274865848
Signed-off-by: T.J. Mercier <tjmercier@google.com>