(07/13) Page reclaims

There are 5 LRU lists for below pages;

  * Active anon page 
  * Inactive anon page 
  * Active file page (page cache)
  * inactive file page (page cache)
  * Unevictable page 

https://elixir.bootlin.com/linux/v5.15.30/source/include/linux/mmzone.h#L272
enum lru_list {
	LRU_INACTIVE_ANON = LRU_BASE,
	LRU_ACTIVE_ANON = LRU_BASE + LRU_ACTIVE,
	LRU_INACTIVE_FILE = LRU_BASE + LRU_FILE,
	LRU_ACTIVE_FILE = LRU_BASE + LRU_FILE + LRU_ACTIVE,
	LRU_UNEVICTABLE,
	NR_LRU_LISTS
};