void meminfo(void){
  ……
  {"Cached",       &kb_page_cache},  // important
  {"MemFree",      &kb_main_free},    // important
  {"MemTotal",     &kb_main_total},   // important
  {"SReclaimable", &kb_slab_reclaimable}, // "slab reclaimable" (dentry and inode structures)
  {"Slab",         &kb_slab},         // kB version of vmstat nr_slab
  };

  ……
  kb_main_cached = kb_page_cache + kb_slab_reclaimable; // 区别在这里
  kb_swap_used = kb_swap_total - kb_swap_free;

  mem_used = kb_main_total - kb_main_free - kb_main_cached - kb_main_buffers;
  if (mem_used < 0)
    mem_used = kb_main_total - kb_main_free;
  kb_main_used = (unsigned long)mem_used;