Function sf_buf_free

freebsd/kern/subr_sfbuf.c:176–196

* Remove a reference from the given sf_buf, adding it to the free * list when its reference count reaches zero. A freed sf_buf still, * however, retains its virtual-to-physical mapping until it is * recycled or reactivated by sf_buf_alloc(9). */

 * recycled or reactivated by sf_buf_alloc(9).
 */
void
sf_buf_free(struct sf_buf *sf)
{

	if (PMAP_HAS_DMAP)
		return;

	mtx_lock(&sf_buf_lock);
	sf->ref_count--;
	if (sf->ref_count == 0) {
		TAILQ_INSERT_TAIL(&sf_buf_freelist, sf, free_entry);
		nsfbufsused--;
		if (sf_buf_unmap(sf)) {
			sf->m = NULL;
			LIST_REMOVE(sf, list_entry);
		}
		if (sf_buf_alloc_want > 0)
			wakeup(&sf_buf_freelist);
	}
	mtx_unlock(&sf_buf_lock);
}

void
sf_buf_ref(struct sf_buf *sf)