vm_objec.c

open bsd vm device design

		if (object->pager == pager) {
			TAILQ_REMOVE(bucket, entry, hash_links);
			free((caddr_t)entry, M_VMOBJHASH);
			break;
		}
	}
}

/*
 *	vm_object_cache_clear removes all objects from the cache.
 *
 */
void
vm_object_cache_clear()
{
	register vm_object_t	object;

	/*
	 *	Remove each object in the cache by scanning down the
	 *	list of cached objects.
	 */
	vm_object_cache_lock();
	while ((object = vm_object_cached_list.tqh_first) != NULL) {
		vm_object_cache_unlock();

		/* 
		 * Note: it is important that we use vm_object_lookup
		 * to gain a reference, and not vm_object_reference, because
		 * the logic for removing an object from the cache lies in 
		 * lookup.
		 */
		if (object != vm_object_lookup(object->pager))
			panic("vm_object_cache_clear: I'm sooo confused.");
		pager_cache(object, FALSE);

		vm_object_cache_lock();
	}
	vm_object_cache_unlock();
}

boolean_t	vm_object_collapse_allowed = TRUE;
/*
 *	vm_object_collapse:
 *
 *	Collapse an object with the object backing it.
 *	Pages in the backing object are moved into the
 *	parent, and the backing object is deallocated.
 *
 *	Requires that the object be locked and the page
 *	queues be unlocked.
 *
 */
void
vm_object_collapse(object)
	register vm_object_t	object;

{
	register vm_object_t	backing_object;
	register vm_offset_t	backing_offset;
	register vm_size_t	size;
	register vm_offset_t	new_offset;
	register vm_page_t	p, pp;

	if (!vm_object_collapse_allowed)
		return;

	while (TRUE) {
		/*
		 *	Verify that the conditions are right for collapse:
		 *
		 *	The object exists and no pages in it are currently
		 *	being paged out (or have ever been paged out).
		 */
		if (object == NULL ||
		    object->paging_in_progress != 0 ||
		    object->pager != NULL)
			return;

		/*
		 *		There is a backing object, and
		 */
	
		if ((backing_object = object->shadow) == NULL)
			return;
	
		vm_object_lock(backing_object);
		/*
		 *	...
		 *		The backing object is not read_only,
		 *		and no pages in the backing object are
		 *		currently being paged out.
		 *		The backing object is internal.
		 */
	
		if ((backing_object->flags & OBJ_INTERNAL) == 0 ||
		    backing_object->paging_in_progress != 0) {
			vm_object_unlock(backing_object);
			return;
		}
	
		/*
		 *	The backing object can't be a copy-object:
		 *	the shadow_offset for the copy-object must stay
		 *	as 0.  Furthermore (for the 'we have all the
		 *	pages' case), if we bypass backing_object and
		 *	just shadow the next object in the chain, old
		 *	pages from that object would then have to be copied
		 *	BOTH into the (former) backing_object and into the
		 *	parent object.
		 */
		if (backing_object->shadow != NULL &&
		    backing_object->shadow->copy != NULL) {
			vm_object_unlock(backing_object);
			return;
		}

		/*
		 *	We know that we can either collapse the backing
		 *	object (if the parent is the only reference to
		 *	it) or (perhaps) remove the parent's reference
		 *	to it.
		 */

		backing_offset = object->shadow_offset;
		size = object->size;

		/*
		 *	If there is exactly one reference to the backing
		 *	object, we can collapse it into the parent.
		 */
	
		if (backing_object->ref_count == 1) {

			/*
			 *	We can collapse the backing object.
			 *
			 *	Move all in-memory pages from backing_object
			 *	to the parent.  Pages that have been paged out
			 *	will be overwritten by any of the parent's
			 *	pages that shadow them.
			 */

			while ((p = backing_object->memq.tqh_first) != NULL) {
				new_offset = (p->offset - backing_offset);

				/*
				 *	If the parent has a page here, or if
				 *	this page falls outside the parent,
				 *	dispose of it.
				 *
				 *	Otherwise, move it as planned.
				 */

				if (p->offset < backing_offset ||
				    new_offset >= size) {
					vm_page_lock_queues();
					vm_page_free(p);
					vm_page_unlock_queues();
				} else {
				    pp = vm_page_lookup(object, new_offset);
				    if (pp != NULL && !(pp->flags & PG_FAKE)) {
					vm_page_lock_queues();
					vm_page_free(p);
					vm_page_unlock_queues();
				    }
				    else {
					if (pp) {
					    /* may be someone waiting for it */
					    PAGE_WAKEUP(pp);
					    vm_page_lock_queues();
					    vm_page_free(pp);
					    vm_page_unlock_queues();
					}
					vm_page_rename(p, object, new_offset);
				    }
				}
			}

			/*
			 *	Move the pager from backing_object to object.
			 *
			 *	XXX We're only using part of the paging space
			 *	for keeps now... we ought to discard the
			 *	unused portion.
			 */

			if (backing_object->pager) {
				object->pager = backing_object->pager;
				object->paging_offset = backing_offset +
					backing_object->paging_offset;
				backing_object->pager = NULL;
			}

			/*
			 *	Object now shadows whatever backing_object did.
			 *	Note that the reference to backing_object->shadow
			 *	moves from within backing_object to within object.
			 */

			object->shadow = backing_object->shadow;
			object->shadow_offset += backing_object->shadow_offset;
			if (object->shadow != NULL &&
			    object->shadow->copy != NULL) {
				panic("vm_object_collapse: we collapsed a copy-object!");
			}
			/*
			 *	Discard backing_object.
			 *
			 *	Since the backing object has no pages, no
			 *	pager left, and no object references within it,
			 *	all that is necessary is to dispose of it.
			 */

			vm_object_unlock(backing_object);

			simple_lock(&vm_object_list_lock);
			TAILQ_REMOVE(&vm_object_list, backing_object,
			    object_list);
			vm_object_count--;
			simple_unlock(&vm_object_list_lock);

			free((caddr_t)backing_object, M_VMOBJ);

			object_collapses++;
		}
		else {
			/*
			 *	If all of the pages in the backing object are
			 *	shadowed by the parent object, the parent
			 *	object no longer has to shadow the backing
			 *	object; it can shadow the next one in the
			 *	chain.
			 *
			 *	The backing object must not be paged out - we'd
			 *	have to check all of the paged-out pages, as
			 *	well.
			 */

			if (backing_object->pager != NULL) {
				vm_object_unlock(backing_object);
				return;
			}

			/*
			 *	Should have a check for a 'small' number
			 *	of pages here.
			 */

			for (p = backing_object->memq.tqh_first;
			     p != NULL;
			     p = p->listq.tqe_next) {
				new_offset = (p->offset - backing_offset);

				/*
				 *	If the parent has a page here, or if
				 *	this page falls outside the parent,
				 *	keep going.
				 *
				 *	Otherwise, the backing_object must be
				 *	left in the chain.
				 */

				if (p->offset >= backing_offset &&
				    new_offset < size &&
				    ((pp = vm_page_lookup(object, new_offset))
				      == NULL ||
				     (pp->flags & PG_FAKE))) {
					/*
					 *	Page still needed.
					 *	Can't go any further.
					 */
					vm_object_unlock(backing_object);
					return;
				}
			}

			/*
			 *	Make the parent shadow the next object
			 *	in the chain.  Deallocating backing_object
			 *	will not remove it, since its reference
			 *	count is at least 2.
			 */

			object->shadow = backing_object->shadow;
			vm_object_reference(object->shadow);
			object->shadow_offset += backing_object->shadow_offset;

			/*
			 *	Backing object might have had a copy pointer
			 *	to us.  If it did, clear it. 
			 */
			if (backing_object->copy == object) {
				backing_object->copy = NULL;
			}
	
			/*	Drop the reference count on backing_object.
			 *	Since its ref_count was at least 2, it
			 *	will not vanish; so we don't need to call
			 *	vm_object_deallocate.
			 */
			backing_object->ref_count--;
			vm_object_unlock(backing_object);

			object_bypasses ++;

		}

		/*
		 *	Try again with this object's new backing object.
		 */
	}
}

/*
 *	vm_object_page_remove: [internal]
 *
 *	Removes all physical pages in the specified
 *	object range from the object's list of pages.
 *
 *	The object must be locked.
 */
void
vm_object_page_remove(object, start, end)
	register vm_object_t	object;
	register vm_offset_t	start;
	register vm_offset_t	end;
{
	register vm_page_t	p, next;

	if (object == NULL)
		return;

	for (p = object->memq.tqh_first; p != NULL; p = next) {
		next = p->listq.tqe_next;
		if ((start <= p->offset) && (p->offset < end)) {
			pmap_page_protect(VM_PAGE_TO_PHYS(p), VM_PROT_NONE);
			vm_page_lock_queues();
			vm_page_free(p);
			vm_page_unlock_queues();
		}
	}
}

/*
 *	Routine:	vm_object_coalesce
 *	Function:	Coalesces two objects backing up adjoining
 *			regions of memory into a single object.
 *
 *	returns TRUE if objects were combined.
 *
 *	NOTE:	Only works at the moment if the second object is NULL -
 *		if it's not, which object do we lock first?
 *
 *	Parameters:
 *		prev_object	First object to coalesce
 *		prev_offset	Offset into prev_object
 *		next_object	Second object into coalesce
 *		next_offset	Offset into next_object
 *
 *		prev_size	Size of reference to prev_object
 *		next_size	Size of reference to next_object
 *
 *	Conditions:
 *	The object must *not* be locked.
 */
boolean_t
vm_object_coalesce(prev_object, next_object,
			prev_offset, next_offset,
			prev_size, next_size)

	register vm_object_t	prev_object;
	vm_object_t	next_object;
	vm_offset_t	prev_offset, next_offset;
	vm_size_t	prev_size, next_size;
{
	vm_size_t	newsize;

#ifdef	lint
	next_offset++;
#endif

	if (next_object != NULL) {
		return(FALSE);
	}

	if (prev_object == NULL) {
		return(TRUE);
	}

	vm_object_lock(prev_object);

	/*
	 *	Try to collapse the object first
	 */
	vm_object_collapse(prev_object);

	/*
	 *	Can't coalesce if:
	 *	. more than one reference
	 *	. paged out
	 *	. shadows another object
	 *	. has a copy elsewhere
	 *	(any of which mean that the pages not mapped to
	 *	prev_entry may be in use anyway)
	 */

	if (prev_object->ref_count > 1 ||
		prev_object->pager != NULL ||
		prev_object->shadow != NULL ||
		prev_object->copy != NULL) {
		vm_object_unlock(prev_object);
		return(FALSE);
	}

	/*
	 *	Remove any pages that may still be in the object from
	 *	a previous deallocation.
	 */

	vm_object_page_remove(prev_object,
			prev_offset + prev_size,
			prev_offset + prev_size + next_size);

	/*
	 *	Extend the object if necessary.
	 */
	newsize = prev_offset + prev_size + next_size;
	if (newsize > prev_object->size)
		prev_object->size = newsize;

	vm_object_unlock(prev_object);
	return(TRUE);
}

/*
 *	vm_object_print:	[ debug ]
 */
void
vm_object_print(object, full)
	vm_object_t	object;
	boolean_t	full;
{
	register vm_page_t	p;
	extern indent;

	register int count;

	if (object == NULL)
		return;

	iprintf("Object 0x%x: size=0x%x, res=%d, ref=%d, ",
		(int) object, (int) object->size,
		object->resident_page_count, object->ref_count);
	printf("pager=0x%x+0x%x, shadow=(0x%x)+0x%x\n",
	       (int) object->pager, (int) object->paging_offset,
	       (int) object->shadow, (int) object->shadow_offset);
	printf("cache: next=0x%x, prev=0x%x\n",
	       object->cached_list.tqe_next, object->cached_list.tqe_prev);

	if (!full)
		return;

	indent += 2;
	count = 0;
	for (p = object->memq.tqh_first; p != NULL; p = p->listq.tqe_next) {
		if (count == 0)
			iprintf("memory:=");
		else if (count == 6) {
			printf("\n");
			iprintf(" ...");
			count = 0;
		} else
			printf(",");
		count++;

		printf("(off=0x%x,page=0x%x)", p->offset, VM_PAGE_TO_PHYS(p));
	}
	if (count != 0)
		printf("\n");
	indent -= 2;
}