void*
 ft_entry_evict(enum palloc_flags flags) {
   struct list_elem* e;
   //return NULL;
   lock_acquire(&ft_lock);

   for (;;) {
     struct ft_entry* ft_e = list_entry(e, struct ft_entry, elem);
     struct sp_entry* sp_e = ft_e->sp_e;
     if (pagedir_is_accessed(thread_current()->pagedir, sp_e->u_virtual_address)) {
       pagedir_set_accessed(thread_current()->pagedir, sp_e->u_virtual_address, false);
     } else {
       if (pagedir_is_dirty(thread_current()->pagedir, sp_e->u_virtual_address) || sp_e->mem_type == SWAP) {
         sp_e->swap_index = s_out(ft_e->frame);
       }
       sp_e->loaded = false;
       list_remove(&ft_e->elem);
       pagedir_clear_page(thread_current()->pagedir, sp_e->u_virtual_address);
       palloc_free_page(ft_e->frame);
       free(ft_e);
       return palloc_get_page(flags);
     }
     e = list_next(e);
     if(e==list_end(&ft_list)) {
       e= list_begin(&ft_list);
     }
   }
 }