mm: multi-gen LRU: per-node lru_gen_folio lists

For each node, memcgs are divided into two generations: the old and
the young. For each generation, memcgs are randomly sharded into
multiple bins to improve scalability. For each bin, an RCU hlist_nulls
is virtually divided into three segments: the head, the tail and the
default.

An onlining memcg is added to the tail of a random bin in the old
generation. The eviction starts at the head of a random bin in the old
generation. The per-node memcg generation counter, whose reminder (mod
2) indexes the old generation, is incremented when all its bins become
empty.

There are four operations:
1. MEMCG_LRU_HEAD, which moves an memcg to the head of a random bin in
   its current generation (old or young) and updates its "seg" to
   "head";
2. MEMCG_LRU_TAIL, which moves an memcg to the tail of a random bin in
   its current generation (old or young) and updates its "seg" to
   "tail";
3. MEMCG_LRU_OLD, which moves an memcg to the head of a random bin in
   the old generation, updates its "gen" to "old" and resets its "seg"
   to "default";
4. MEMCG_LRU_YOUNG, which moves an memcg to the tail of a random bin
   in the young generation, updates its "gen" to "young" and resets
   its "seg" to "default".

The events that trigger the above operations are:
1. Exceeding the soft limit, which triggers MEMCG_LRU_HEAD;
2. The first attempt to reclaim an memcg below low, which triggers
   MEMCG_LRU_TAIL;
3. The first attempt to reclaim an memcg below reclaimable size
   threshold, which triggers MEMCG_LRU_TAIL;
4. The second attempt to reclaim an memcg below reclaimable size
   threshold, which triggers MEMCG_LRU_YOUNG;
5. Attempting to reclaim an memcg below min, which triggers
   MEMCG_LRU_YOUNG;
6. Finishing the aging on the eviction path, which triggers
   MEMCG_LRU_YOUNG;
7. Offlining an memcg, which triggers MEMCG_LRU_OLD.

Note that memcg LRU only applies to global reclaim, and the
round-robin incrementing of their max_seq counters ensures the
eventual fairness to all eligible memcgs. For memcg reclaim, it still
relies on mem_cgroup_iter().

Link: https://lkml.kernel.org/r/20221222041905.2431096-7-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, 16 insertions, 0 deletions

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 49f67176a1a2d..2758b67eb169c 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -478,6 +478,16 @@ static void mem_cgroup_update_tree(struct mem_cgroup *memcg, int nid)
 	struct mem_cgroup_per_node *mz;
 	struct mem_cgroup_tree_per_node *mctz;
 
+	if (lru_gen_enabled()) {
+		struct lruvec *lruvec = &memcg->nodeinfo[nid]->lruvec;
+
+		/* see the comment on MEMCG_NR_GENS */
+		if (soft_limit_excess(memcg) && lru_gen_memcg_seg(lruvec) != MEMCG_LRU_HEAD)
+			lru_gen_rotate_memcg(lruvec, MEMCG_LRU_HEAD);
+
+		return;
+	}
+
 	mctz = soft_limit_tree.rb_tree_per_node[nid];
 	if (!mctz)
 		return;
@@ -3530,6 +3540,9 @@ unsigned long mem_cgroup_soft_limit_reclaim(pg_data_t *pgdat, int order,
 	struct mem_cgroup_tree_per_node *mctz;
 	unsigned long excess;
 
+	if (lru_gen_enabled())
+		return 0;
+
 	if (order > 0)
 		return 0;
 
@@ -5391,6 +5404,7 @@ static int mem_cgroup_css_online(struct cgroup_subsys_state *css)
 	if (unlikely(mem_cgroup_is_root(memcg)))
 		queue_delayed_work(system_unbound_wq, &stats_flush_dwork,
 				   2UL*HZ);
+	lru_gen_online_memcg(memcg);
 	return 0;
 offline_kmem:
 	memcg_offline_kmem(memcg);
@@ -5422,6 +5436,7 @@ static void mem_cgroup_css_offline(struct cgroup_subsys_state *css)
 	memcg_offline_kmem(memcg);
 	reparent_shrinker_deferred(memcg);
 	wb_memcg_offline(memcg);
+	lru_gen_offline_memcg(memcg);
 
 	drain_all_stock(memcg);
 
@@ -5433,6 +5448,7 @@ static void mem_cgroup_css_released(struct cgroup_subsys_state *css)
 	struct mem_cgroup *memcg = mem_cgroup_from_css(css);
 
 	invalidate_reclaim_iterators(memcg);
+	lru_gen_release_memcg(memcg);
 }
 
 static void mem_cgroup_css_free(struct cgroup_subsys_state *css)