Function vm_object_madvise

freebsd/vm/vm_object.c:1304–1405

* vm_object_madvise: * * Implements the madvise function at the object/page level. * * MADV_WILLNEED (any object) * * Activate the specified pages if they are resident. * * MADV_DONTNEED (any object) * * Deactivate the specified pages if they are resident. * * MADV_FREE (OBJT_DEFAULT/OBJT_SWAP objects, * OBJ_ONEMAPPING only) * * Deactivate and clean the specified page

 *	    without I/O.
 */
void
vm_object_madvise(vm_object_t object, vm_pindex_t pindex, vm_pindex_t end,
    int advice)
{
	vm_pindex_t tpindex;
	vm_object_t backing_object, tobject;
	vm_page_t m, tm;

	if (object == NULL)
		return;

relookup:
	VM_OBJECT_WLOCK(object);
	if (!vm_object_advice_applies(object, advice)) {
		VM_OBJECT_WUNLOCK(object);
		return;
	}
	for (m = vm_page_find_least(object, pindex); pindex < end; pindex++) {
		tobject = object;

		/*
		 * If the next page isn't resident in the top-level object, we
		 * need to search the shadow chain.  When applying MADV_FREE, we
		 * take care to release any swap space used to store
		 * non-resident pages.
		 */
		if (m == NULL || pindex < m->pindex) {
			/*
			 * Optimize a common case: if the top-level object has
			 * no backing object, we can skip over the non-resident
			 * range in constant time.
			 */
			if (object->backing_object == NULL) {
				tpindex = (m != NULL && m->pindex < end) ?
				    m->pindex : end;
				vm_object_madvise_freespace(object, advice,
				    pindex, tpindex - pindex);
				if ((pindex = tpindex) == end)
					break;
				goto next_page;
			}

			tpindex = pindex;
			do {
				vm_object_madvise_freespace(tobject, advice,
				    tpindex, 1);
				/*
				 * Prepare to search the next object in the
				 * chain.
				 */
				backing_object = tobject->backing_object;
				if (backing_object == NULL)
					goto next_pindex;
				VM_OBJECT_WLOCK(backing_object);
				tpindex +=
				    OFF_TO_IDX(tobject->backing_object_offset);
				if (tobject != object)
					VM_OBJECT_WUNLOCK(tobject);