void hold_metapage(struct metapage * mp, int force)
extern void hold_metapage(struct metapage *mp)
void hold_metapage(struct metapage * mp, int force){	spin_lock(&meta_lock);	mp->count++;	if (force) {		ASSERT (!(test_bit(META_forced, &mp->flag)));		if (trylock_metapage(mp))			set_bit(META_forced, &mp->flag);	} else		lock_metapage(mp);	spin_unlock(&meta_lock);}