Function vm_page_replace_hold

freebsd/vm/vm_page.c:1836–1880

* Uses the page mnew as a replacement for an existing page at index * pindex which must be already present in the object. * * Both pages must be exclusively busied on enter. The old page is * unbusied on exit. * * A return value of true means mold is now free. If this is not the * final ref and the caller does not hold a wire reference it may not * continue to access the page. */

 * continue to access the page.
 */
static bool
vm_page_replace_hold(vm_page_t mnew, vm_object_t object, vm_pindex_t pindex,
    vm_page_t mold)
{
	vm_page_t mret;
	bool dropped;

	VM_OBJECT_ASSERT_WLOCKED(object);
	vm_page_assert_xbusied(mold);
	KASSERT(mnew->object == NULL && (mnew->ref_count & VPRC_OBJREF) == 0,
	    ("vm_page_replace: page %p already in object", mnew));

	/*
	 * This function mostly follows vm_page_insert() and
	 * vm_page_remove() without the radix, object count and vnode
	 * dance.  Double check such functions for more comments.
	 */

	mnew->object = object;
	mnew->pindex = pindex;
	atomic_set_int(&mnew->ref_count, VPRC_OBJREF);
	mret = vm_radix_replace(&object->rtree, mnew);
	KASSERT(mret == mold,
	    ("invalid page replacement, mold=%p, mret=%p", mold, mret));
	KASSERT((mold->oflags & VPO_UNMANAGED) ==
	    (mnew->oflags & VPO_UNMANAGED),
	    ("vm_page_replace: mismatched VPO_UNMANAGED"));

	/* Keep the resident page list in sorted order. */
	TAILQ_INSERT_AFTER(&object->memq, mold, mnew, listq);
	TAILQ_REMOVE(&object->memq, mold, listq);
	mold->object = NULL;

	/*
	 * The object's resident_page_count does not change because we have
	 * swapped one page for another, but the generation count should
	 * change if the page is dirty.
	 */
	if (pmap_page_is_write_mapped(mnew))
		vm_object_set_writeable_dirty(object);
	dropped = vm_page_drop(mold, VPRC_OBJREF) == VPRC_OBJREF;
	vm_page_xunbusy(mold);

	return (dropped);
}

void
vm_page_replace(vm_page_t mnew, vm_object_t object, vm_pindex_t pindex,