mm: multi-gen LRU: rename lru_gen_struct to lru_gen_folio

Patch series "mm: multi-gen LRU: memcg LRU", v3.

Overview
========

An memcg LRU is a per-node LRU of memcgs.  It is also an LRU of LRUs,
since each node and memcg combination has an LRU of folios (see
mem_cgroup_lruvec()).

Its goal is to improve the scalability of global reclaim, which is
critical to system-wide memory overcommit in data centers.  Note that
memcg reclaim is currently out of scope.

Its memory bloat is a pointer to each lruvec and negligible to each
pglist_data.  In terms of traversing memcgs during global reclaim, it
improves the best-case complexity from O(n) to O(1) and does not affect
the worst-case complexity O(n).  Therefore, on average, it has a sublinear
complexity in contrast to the current linear complexity.

The basic structure of an memcg LRU can be understood by an analogy to
the active/inactive LRU (of folios):
1. It has the young and the old (generations), i.e., the counterparts
   to the active and the inactive;
2. The increment of max_seq triggers promotion, i.e., the counterpart
   to activation;
3. Other events trigger similar operations, e.g., offlining an memcg
   triggers demotion, i.e., the counterpart to deactivation.

In terms of global reclaim, it has two distinct features:
1. Sharding, which allows each thread to start at a random memcg (in
   the old generation) and improves parallelism;
2. Eventual fairness, which allows direct reclaim to bail out at will
   and reduces latency without affecting fairness over some time.

The commit message in patch 6 details the workflow:
https://lore.kernel.org/r/20221222041905.2431096-7-yuzhao@google.com/

The following is a simple test to quickly verify its effectiveness.

  Test design:
  1. Create multiple memcgs.
  2. Each memcg contains a job (fio).
  3. All jobs access the same amount of memory randomly.
  4. The system does not experience global memory pressure.
  5. Periodically write to the root memory.reclaim.

  Desired outcome:
  1. All memcgs have similar pgsteal counts, i.e., stddev(pgsteal)
     over mean(pgsteal) is close to 0%.
  2. The total pgsteal is close to the total requested through
     memory.reclaim, i.e., sum(pgsteal) over sum(requested) is close
     to 100%.

  Actual outcome [1]:
                                     MGLRU off    MGLRU on
  stddev(pgsteal) / mean(pgsteal)    75%          20%
  sum(pgsteal) / sum(requested)      425%         95%

  ####################################################################
  MEMCGS=128

  for ((memcg = 0; memcg < $MEMCGS; memcg++)); do
      mkdir /sys/fs/cgroup/memcg$memcg
  done

  start() {
      echo $BASHPID > /sys/fs/cgroup/memcg$memcg/cgroup.procs

      fio -name=memcg$memcg --numjobs=1 --ioengine=mmap \
          --filename=/dev/zero --size=1920M --rw=randrw \
          --rate=64m,64m --random_distribution=random \
          --fadvise_hint=0 --time_based --runtime=10h \
          --group_reporting --minimal
  }

  for ((memcg = 0; memcg < $MEMCGS; memcg++)); do
      start &
  done

  sleep 600

  for ((i = 0; i < 600; i++)); do
      echo 256m >/sys/fs/cgroup/memory.reclaim
      sleep 6
  done

  for ((memcg = 0; memcg < $MEMCGS; memcg++)); do
      grep "pgsteal " /sys/fs/cgroup/memcg$memcg/memory.stat
  done
  ####################################################################

[1]: This was obtained from running the above script (touches less
     than 256GB memory) on an EPYC 7B13 with 512GB DRAM for over an
     hour.


This patch (of 8):

The new name lru_gen_folio will be more distinct from the coming
lru_gen_memcg.

Link: https://lkml.kernel.org/r/20221222041905.2431096-1-yuzhao@google.com
Link: https://lkml.kernel.org/r/20221222041905.2431096-2-yuzhao@google.com
Signed-off-by: Yu Zhao <yuzhao@google.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Michael Larabel <Michael@MichaelLarabel.com>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: Roman Gushchin <roman.gushchin@linux.dev>
Cc: Suren Baghdasaryan <surenb@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

1 files changed, 17 insertions, 17 deletions

diff --git a/mm/vmscan.c b/mm/vmscan.c
index aa8c252949da..5505f54871c9 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -3215,7 +3215,7 @@ static int get_nr_gens(struct lruvec *lruvec, int type)
 
 static bool __maybe_unused seq_is_valid(struct lruvec *lruvec)
 {
-	/* see the comment on lru_gen_struct */
+	/* see the comment on lru_gen_folio */
 	return get_nr_gens(lruvec, LRU_GEN_FILE) >= MIN_NR_GENS &&
 	       get_nr_gens(lruvec, LRU_GEN_FILE) <= get_nr_gens(lruvec, LRU_GEN_ANON) &&
 	       get_nr_gens(lruvec, LRU_GEN_ANON) <= MAX_NR_GENS;
@@ -3612,7 +3612,7 @@ struct ctrl_pos {
 static void read_ctrl_pos(struct lruvec *lruvec, int type, int tier, int gain,
 			  struct ctrl_pos *pos)
 {
-	struct lru_gen_struct *lrugen = &lruvec->lrugen;
+	struct lru_gen_folio *lrugen = &lruvec->lrugen;
 	int hist = lru_hist_from_seq(lrugen->min_seq[type]);
 
 	pos->refaulted = lrugen->avg_refaulted[type][tier] +
@@ -3627,7 +3627,7 @@ static void read_ctrl_pos(struct lruvec *lruvec, int type, int tier, int gain,
 static void reset_ctrl_pos(struct lruvec *lruvec, int type, bool carryover)
 {
 	int hist, tier;
-	struct lru_gen_struct *lrugen = &lruvec->lrugen;
+	struct lru_gen_folio *lrugen = &lruvec->lrugen;
 	bool clear = carryover ? NR_HIST_GENS == 1 : NR_HIST_GENS > 1;
 	unsigned long seq = carryover ? lrugen->min_seq[type] : lrugen->max_seq + 1;
 
@@ -3704,7 +3704,7 @@ static int folio_update_gen(struct folio *folio, int gen)
 static int folio_inc_gen(struct lruvec *lruvec, struct folio *folio, bool reclaiming)
 {
 	int type = folio_is_file_lru(folio);
-	struct lru_gen_struct *lrugen = &lruvec->lrugen;
+	struct lru_gen_folio *lrugen = &lruvec->lrugen;
 	int new_gen, old_gen = lru_gen_from_seq(lrugen->min_seq[type]);
 	unsigned long new_flags, old_flags = READ_ONCE(folio->flags);
 
@@ -3749,7 +3749,7 @@ static void update_batch_size(struct lru_gen_mm_walk *walk, struct folio *folio,
 static void reset_batch_size(struct lruvec *lruvec, struct lru_gen_mm_walk *walk)
 {
 	int gen, type, zone;
-	struct lru_gen_struct *lrugen = &lruvec->lrugen;
+	struct lru_gen_folio *lrugen = &lruvec->lrugen;
 
 	walk->batched = 0;
 
@@ -4263,7 +4263,7 @@ static bool inc_min_seq(struct lruvec *lruvec, int type, bool can_swap)
 {
 	int zone;
 	int remaining = MAX_LRU_BATCH;
-	struct lru_gen_struct *lrugen = &lruvec->lrugen;
+	struct lru_gen_folio *lrugen = &lruvec->lrugen;
 	int new_gen, old_gen = lru_gen_from_seq(lrugen->min_seq[type]);
 
 	if (type == LRU_GEN_ANON && !can_swap)
@@ -4299,7 +4299,7 @@ static bool try_to_inc_min_seq(struct lruvec *lruvec, bool can_swap)
 {
 	int gen, type, zone;
 	bool success = false;
-	struct lru_gen_struct *lrugen = &lruvec->lrugen;
+	struct lru_gen_folio *lrugen = &lruvec->lrugen;
 	DEFINE_MIN_SEQ(lruvec);
 
 	VM_WARN_ON_ONCE(!seq_is_valid(lruvec));
@@ -4320,7 +4320,7 @@ next:
 		;
 	}
 
-	/* see the comment on lru_gen_struct */
+	/* see the comment on lru_gen_folio */
 	if (can_swap) {
 		min_seq[LRU_GEN_ANON] = min(min_seq[LRU_GEN_ANON], min_seq[LRU_GEN_FILE]);
 		min_seq[LRU_GEN_FILE] = max(min_seq[LRU_GEN_ANON], lrugen->min_seq[LRU_GEN_FILE]);
@@ -4342,7 +4342,7 @@ static void inc_max_seq(struct lruvec *lruvec, bool can_swap, bool force_scan)
 {
 	int prev, next;
 	int type, zone;
-	struct lru_gen_struct *lrugen = &lruvec->lrugen;
+	struct lru_gen_folio *lrugen = &lruvec->lrugen;
 
 	spin_lock_irq(&lruvec->lru_lock);
 
@@ -4400,7 +4400,7 @@ static bool try_to_inc_max_seq(struct lruvec *lruvec, unsigned long max_seq,
 	bool success;
 	struct lru_gen_mm_walk *walk;
 	struct mm_struct *mm = NULL;
-	struct lru_gen_struct *lrugen = &lruvec->lrugen;
+	struct lru_gen_folio *lrugen = &lruvec->lrugen;
 
 	VM_WARN_ON_ONCE(max_seq > READ_ONCE(lrugen->max_seq));
 
@@ -4465,7 +4465,7 @@ static bool should_run_aging(struct lruvec *lruvec, unsigned long max_seq, unsig
 	unsigned long old = 0;
 	unsigned long young = 0;
 	unsigned long total = 0;
-	struct lru_gen_struct *lrugen = &lruvec->lrugen;
+	struct lru_gen_folio *lrugen = &lruvec->lrugen;
 	struct mem_cgroup *memcg = lruvec_memcg(lruvec);
 
 	for (type = !can_swap; type < ANON_AND_FILE; type++) {
@@ -4750,7 +4750,7 @@ static bool sort_folio(struct lruvec *lruvec, struct folio *folio, int tier_idx)
 	int delta = folio_nr_pages(folio);
 	int refs = folio_lru_refs(folio);
 	int tier = lru_tier_from_refs(refs);
-	struct lru_gen_struct *lrugen = &lruvec->lrugen;
+	struct lru_gen_folio *lrugen = &lruvec->lrugen;
 
 	VM_WARN_ON_ONCE_FOLIO(gen >= MAX_NR_GENS, folio);
 
@@ -4850,7 +4850,7 @@ static int scan_folios(struct lruvec *lruvec, struct scan_control *sc,
 	int scanned = 0;
 	int isolated = 0;
 	int remaining = MAX_LRU_BATCH;
-	struct lru_gen_struct *lrugen = &lruvec->lrugen;
+	struct lru_gen_folio *lrugen = &lruvec->lrugen;
 	struct mem_cgroup *memcg = lruvec_memcg(lruvec);
 
 	VM_WARN_ON_ONCE(!list_empty(list));
@@ -5251,7 +5251,7 @@ done:
 
 static bool __maybe_unused state_is_valid(struct lruvec *lruvec)
 {
-	struct lru_gen_struct *lrugen = &lruvec->lrugen;
+	struct lru_gen_folio *lrugen = &lruvec->lrugen;
 
 	if (lrugen->enabled) {
 		enum lru_list lru;
@@ -5530,7 +5530,7 @@ static void lru_gen_seq_show_full(struct seq_file *m, struct lruvec *lruvec,
 	int i;
 	int type, tier;
 	int hist = lru_hist_from_seq(seq);
-	struct lru_gen_struct *lrugen = &lruvec->lrugen;
+	struct lru_gen_folio *lrugen = &lruvec->lrugen;
 
 	for (tier = 0; tier < MAX_NR_TIERS; tier++) {
 		seq_printf(m, "            %10d", tier);
@@ -5580,7 +5580,7 @@ static int lru_gen_seq_show(struct seq_file *m, void *v)
 	unsigned long seq;
 	bool full = !debugfs_real_fops(m->file)->write;
 	struct lruvec *lruvec = v;
-	struct lru_gen_struct *lrugen = &lruvec->lrugen;
+	struct lru_gen_folio *lrugen = &lruvec->lrugen;
 	int nid = lruvec_pgdat(lruvec)->node_id;
 	struct mem_cgroup *memcg = lruvec_memcg(lruvec);
 	DEFINE_MAX_SEQ(lruvec);
@@ -5834,7 +5834,7 @@ void lru_gen_init_lruvec(struct lruvec *lruvec)
 {
 	int i;
 	int gen, type, zone;
-	struct lru_gen_struct *lrugen = &lruvec->lrugen;
+	struct lru_gen_folio *lrugen = &lruvec->lrugen;
 
 	lrugen->max_seq = MIN_NR_GENS + 1;
 	lrugen->enabled = lru_gen_enabled();