Function cache_hold_vnode

freebsd/kern/vfs_cache.c:541–549

* Directory vnodes with entries are held for two reasons: * 1. make them less of a target for reclamation in vnlru * 2. suffer smaller performance penalty in locked lookup as requeieing is avoided * * It will be feasible to stop doing it altogether if all filesystems start * supporting lockless lookup. */

 * supporting lockless lookup.
 */
static void
cache_hold_vnode(struct vnode *vp)
{

	cache_assert_vnode_locked(vp);
	VNPASS(LIST_EMPTY(&vp->v_cache_src), vp);
	vhold(vp);
	counter_u64_add(numcachehv, 1);
}

static void
cache_drop_vnode(struct vnode *vp)