mm: multigenerational lru: Kconfig

Add configuration options for the multigenerational lru.

Signed-off-by: Yu Zhao <yuzhao@google.com>

mm/Kconfig

@@ -872,4 +872,59 @@ config MAPPING_DIRTY_HELPERS
 config KMAP_LOCAL
 	bool
 
+config LRU_GEN
+	bool "Multigenerational LRU"
+	depends on MMU
+	help
+	  A high performance LRU implementation to heavily overcommit workloads
+	  that are not IO bound. See Documentation/vm/multigen_lru.rst for
+	  details.
+
+	  Warning: do not enable this option unless you plan to use it because
+	  it introduces a small per-process and per-memcg and per-node memory
+	  overhead.
+
+config NR_LRU_GENS
+	int "Max number of generations"
+	depends on LRU_GEN
+	range 4 31
+	default 7
+	help
+	  This will use order_base_2(N+1) spare bits from page flags.
+
+	  Warning: do not use numbers larger than necessary because each
+	  generation introduces a small per-node and per-memcg memory overhead.
+
+config TIERS_PER_GEN
+	int "Number of tiers per generation"
+	depends on LRU_GEN
+	range 2 5
+	default 4
+	help
+	  This will use N-2 spare bits from page flags.
+
+	  Higher values generally offer better protection to active pages under
+	  heavy buffered I/O workloads.
+
+config LRU_GEN_ENABLED
+	bool "Turn on by default"
+	depends on LRU_GEN
+	help
+	  The default value of /sys/kernel/mm/lru_gen/enabled is 0. This option
+	  changes it to 1.
+
+	  Warning: the default value is the fast path. See
+	  Documentation/static-keys.txt for details.
+
+config LRU_GEN_STATS
+	bool "Full stats for debugging"
+	depends on LRU_GEN
+	help
+	  This option keeps full stats for each generation, which can be read
+	  from /sys/kernel/debug/lru_gen_full.
+
+	  Warning: do not enable this option unless you plan to use it because
+	  it introduces an additional small per-process and per-memcg and
+	  per-node memory overhead.
+
 endmenu