Function pmap_clear_modify

freebsd/amd64/amd64/pmap.c:8811–8893

* Clear the modify bits on the specified physical page. */

 *	Clear the modify bits on the specified physical page.
 */
void
pmap_clear_modify(vm_page_t m)
{
	struct md_page *pvh;
	pmap_t pmap;
	pv_entry_t next_pv, pv;
	pd_entry_t oldpde, *pde;
	pt_entry_t *pte, PG_M, PG_RW;
	struct rwlock *lock;
	vm_offset_t va;
	int md_gen, pvh_gen;

	KASSERT((m->oflags & VPO_UNMANAGED) == 0,
	    ("pmap_clear_modify: page %p is not managed", m));
	vm_page_assert_busied(m);

	if (!pmap_page_is_write_mapped(m))
		return;
	pvh = (m->flags & PG_FICTITIOUS) != 0 ? &pv_dummy :
	    pa_to_pvh(VM_PAGE_TO_PHYS(m));
	lock = VM_PAGE_TO_PV_LIST_LOCK(m);
	rw_wlock(lock);
restart:
	TAILQ_FOREACH_SAFE(pv, &pvh->pv_list, pv_next, next_pv) {
		pmap = PV_PMAP(pv);
		if (!PMAP_TRYLOCK(pmap)) {
			pvh_gen = pvh->pv_gen;
			rw_wunlock(lock);
			PMAP_LOCK(pmap);
			rw_wlock(lock);
			if (pvh_gen != pvh->pv_gen) {
				PMAP_UNLOCK(pmap);
				goto restart;
			}
		}
		PG_M = pmap_modified_bit(pmap);
		PG_RW = pmap_rw_bit(pmap);
		va = pv->pv_va;
		pde = pmap_pde(pmap, va);
		oldpde = *pde;
		/* If oldpde has PG_RW set, then it also has PG_M set. */
		if ((oldpde & PG_RW) != 0 &&
		    pmap_demote_pde_locked(pmap, pde, va, &lock) &&
		    (oldpde & PG_W) == 0) {
			/*
			 * Write protect the mapping to a single page so that
			 * a subsequent write access may repromote.
			 */
			va += VM_PAGE_TO_PHYS(m) - (oldpde & PG_PS_FRAME);
			pte = pmap_pde_to_pte(pde, va);
			atomic_clear_long(pte, PG_M | PG_RW);
			vm_page_dirty(m);
			pmap_invalidate_page(pmap, va);
		}
		PMAP_UNLOCK(pmap);
	}
	TAILQ_FOREACH(pv, &m->md.pv_list, pv_next) {
		pmap = PV_PMAP(pv);