BACKPORT: FROMLIST: mm: multigenerational lru: groundwork

For each lruvec, evictable pages are divided into multiple
generations. The youngest generation number is stored in
lrugen->max_seq for both anon and file types as they are aged on an
equal footing. The oldest generation numbers are stored in
lrugen->min_seq[2] separately for anon and file types as clean file
pages can be evicted regardless of swap and writeback constraints.
These three variables are monotonically increasing. Generation numbers
are truncated into order_base_2(MAX_NR_GENS+1) bits in order to fit
into page->flags. The sliding window technique is used to prevent
truncated generation numbers from overlapping. Each truncated
generation number is an index to
lrugen->lists[MAX_NR_GENS][ANON_AND_FILE][MAX_NR_ZONES].

Each generation is then divided into multiple tiers. Tiers represent
levels of usage from file descriptors only. Pages accessed N times via
file descriptors belong to tier order_base_2(N). Each generation
contains at most MAX_NR_TIERS tiers, and they require additional
MAX_NR_TIERS-2 bits in page->flags. In contrast to moving across
generations which requires list operations, moving across tiers only
involves operations on page->flags and therefore has a negligible
cost. A feedback loop modeled after the PID controller monitors
refault rates of all tiers and decides when to protect pages from
which tiers.

The framework comprises two conceptually independent components: the
aging and the eviction, which can be invoked separately from user
space for the purpose of working set estimation and proactive reclaim.

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 (a mm_struct list is maintained for each
memcg). 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 eviction consumes old generations. Given an lruvec, the eviction
scans pages on lrugen->lists indexed by anon and file min_seq[2]
(modulo MAX_NR_GENS). It first tries to select a type based on the
values of min_seq[2]. If they are equal, it selects the type that has
a lower refault rate. The eviction sorts a page according to its
updated generation number if the aging has found this page accessed.
It also moves a page to the next generation if this page is from an
upper tier that has a higher refault rate than the base tier. The
eviction increments min_seq[2] of a selected type when it finds
lrugen->lists indexed by min_seq[2] of this selected type are empty.

Signed-off-by: Yu Zhao <yuzhao@google.com>
Tested-by: Konstantin Kharlamov <Hi-Angel@yandex.ru>
(am from https://lore.kernel.org/patchwork/patch/1478357/)

BUG=b:123039911
TEST=Built

Change-Id: I71de7cd15b8dfa6f9fdd838023474693c4fee0a7
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/third_party/kernel/+/3132021


Tested-by: Yu Zhao <yuzhao@chromium.org>
Commit-Queue: Yu Zhao <yuzhao@chromium.org>
Reviewed-by: Sergey Senozhatsky <senozhatsky@chromium.org>