Function pmap_ts_referenced

freebsd/arm/arm/pmap-v6.c:5303–5405

* pmap_ts_referenced: * * Return a count of reference bits for a page, clearing those bits. * It is not necessary for every reference bit to be cleared, but it * is necessary that 0 only be returned when there are truly no * reference bits set. * * As an optimization, update the page's dirty field if a modified bit is * found while counting reference bits. This opportunistic update can be

 *	to pmap_is_modified().
 */
int
pmap_ts_referenced(vm_page_t m)
{
	struct md_page *pvh;
	pv_entry_t pv, pvf;
	pmap_t pmap;
	pt1_entry_t  *pte1p, opte1;
	pt2_entry_t *pte2p, opte2;
	vm_paddr_t pa;
	int rtval = 0;

	KASSERT((m->oflags & VPO_UNMANAGED) == 0,
	    ("%s: page %p is not managed", __func__, m));
	pa = VM_PAGE_TO_PHYS(m);
	pvh = pa_to_pvh(pa);
	rw_wlock(&pvh_global_lock);
	sched_pin();
	if ((m->flags & PG_FICTITIOUS) != 0 ||
	    (pvf = TAILQ_FIRST(&pvh->pv_list)) == NULL)
		goto small_mappings;
	pv = pvf;
	do {
		pmap = PV_PMAP(pv);
		PMAP_LOCK(pmap);
		pte1p = pmap_pte1(pmap, pv->pv_va);
		opte1 = pte1_load(pte1p);
		if (pte1_is_dirty(opte1)) {
			/*
			 * Although "opte1" is mapping a 1MB page, because
			 * this function is called at a 4KB page granularity,
			 * we only update the 4KB page under test.
			 */
			vm_page_dirty(m);
		}
		if ((opte1 & PTE1_A) != 0) {
			/*
			 * Since this reference bit is shared by 256 4KB pages,
			 * it should not be cleared every time it is tested.
			 * Apply a simple "hash" function on the physical page
			 * number, the virtual section number, and the pmap
			 * address to select one 4KB page out of the 256
			 * on which testing the reference bit will result
			 * in clearing that bit. This function is designed
			 * to avoid the selection of the same 4KB page
			 * for every 1MB page mapping.
			 *
			 * On demotion, a mapping that hasn't been referenced
			 * is simply destroyed.  To avoid the possibility of a
			 * subsequent page fault on a demoted wired mapping,
			 * always leave its reference bit set.  Moreover,
			 * since the section is wired, the current state of
			 * its reference bit won't affect page replacement.
			 */
			 if ((((pa >> PAGE_SHIFT) ^ (pv->pv_va >> PTE1_SHIFT) ^
			    (uintptr_t)pmap) & (NPTE2_IN_PG - 1)) == 0 &&
			    !pte1_is_wired(opte1)) {
				pte1_clear_bit(pte1p, PTE1_A);
				pmap_tlb_flush(pmap, pv->pv_va);