BACKPORT: FROMLIST: mm: multigenerational lru: aging

The aging produces young generations. Given an lruvec, the aging
traverses lruvec_memcg()->mm_list and calls walk_page_range() to scan
PTEs for accessed pages. Upon finding one, the aging updates its
generation number to max_seq (modulo MAX_NR_GENS). After each round of
traversal, the aging increments max_seq. The aging is due when both
min_seq[2] have caught up with max_seq-1.

The aging uses the following optimizations when walking page tables:
  1) It skips page tables of processes that have been sleeping since
  the last walk.
  2) It skips non-leaf PMD entries that have the accessed bit cleared
  when CONFIG_ARCH_HAS_NONLEAF_PMD_YOUNG=y.
  3) It does not zigzag between a PGD table and the same PMD or PTE
  table spanning multiple VMAs. In other words, it finishes all the
  VMAs within the range of the same PMD or PTE table before it returns
  to this PGD table. This optimizes workloads that have large numbers
  of tiny VMAs, especially when CONFIG_PGTABLE_LEVELS=5.

Signed-off-by: Yu Zhao <yuzhao@google.com>
Tested-by: Konstantin Kharlamov <Hi-Angel@yandex.ru>
(am from https://lore.kernel.org/patchwork/patch/1478360/)

BUG=b:123039911
TEST=Built

Change-Id: I3ae8abc3100d023cecb3a699d86020ae6fc10a45
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/third_party/kernel/+/3132024


Tested-by: Yu Zhao <yuzhao@chromium.org>
Commit-Queue: Yu Zhao <yuzhao@chromium.org>
Reviewed-by: Sergey Senozhatsky <senozhatsky@chromium.org>
Reviewed-by: Alexandre Marciano Gimenez <raging@google.com>