PG_unevictable
u |= kpf_copy_bit(k, KPF_UNEVICTABLE, PG_unevictable);
1UL << PG_unevictable | __PG_MLOCKED | LRU_GEN_MASK)
(1L << PG_unevictable) |
#define unevict (1UL << PG_unevictable)