kernel/vm: Introduce and use VMAddressSpace::AreaRangeIterator.

It iterates over all areas intersecting a given address range and
removes the need for manually skipping uninteresting initial areas. It
uses VMAddressSpace::FindClosestArea() to efficiently find the starting
area.

This speeds up the two iterations in unmap_address_range and one in
wait_if_address_range_is_wired and resolves a TODO in the latter hinting
at such a solution.

Change-Id: Iba1d39942db4e4b27e17706be194496f9d4279ed
Reviewed-on: https://review.haiku-os.org/c/haiku/+/2841
Reviewed-by: waddlesplash <[email protected]>

headers/private/kernel/vm/VMAddressSpace.h

@@ -23,6 +23,7 @@ struct virtual_address_restrictions;
 struct VMAddressSpace {
 public:
 			class AreaIterator;
+			class AreaRangeIterator;
 
 public:
 								VMAddressSpace(team_id id, addr_t base,
@@ -67,6 +68,8 @@ public:
 									{ fRandomizingEnabled = enabled; }
 
 	inline	AreaIterator		GetAreaIterator();
+	inline	AreaRangeIterator	GetAreaRangeIterator(addr_t address,
+									addr_t size);
 
 			VMAddressSpace*&	HashTableLink()	{ return fHashTableLink; }
 
@@ -202,6 +205,54 @@ private:
 };
 
 
+class VMAddressSpace::AreaRangeIterator : public VMAddressSpace::AreaIterator {
+public:
+	AreaRangeIterator()
+	{
+	}
+
+	AreaRangeIterator(VMAddressSpace* addressSpace, addr_t address, addr_t size)
+		:
+		fAddressSpace(addressSpace),
+		fNext(NULL),
+		fAddress(address),
+		fEndAddress(address + size - 1)
+	{
+		Rewind();
+	}
+
+	bool HasNext() const
+	{
+		return fNext != NULL;
+	}
+
+	VMArea* Next()
+	{
+		VMArea* result = fNext;
+		if (fNext != NULL) {
+			fNext = fAddressSpace->NextArea(fNext);
+			if (fNext != NULL && fNext->Base() > fEndAddress)
+				fNext = NULL;
+		}
+
+		return result;
+	}
+
+	void Rewind()
+	{
+		fNext = fAddressSpace->FindClosestArea(fAddress, true);
+		if (fNext != NULL && !fNext->ContainsAddress(fAddress))
+			Next();
+	}
+
+private:
+	VMAddressSpace*	fAddressSpace;
+	VMArea*			fNext;
+	addr_t			fAddress;
+	addr_t			fEndAddress;
+};
+
+
 inline VMAddressSpace::AreaIterator
 VMAddressSpace::GetAreaIterator()
 {
@@ -209,6 +260,13 @@ VMAddressSpace::GetAreaIterator()
 }
 
 
+inline VMAddressSpace::AreaRangeIterator
+VMAddressSpace::GetAreaRangeIterator(addr_t address, addr_t size)
+{
+	return AreaRangeIterator(this, address, size);
+}
+
+
 #ifdef __cplusplus
 extern "C" {
 #endif

src/system/kernel/vm/vm.cpp

@@ -833,14 +833,13 @@ unmap_address_range(VMAddressSpace* addressSpace, addr_t address, addr_t size,
 	bool kernel)
 {
 	size = PAGE_ALIGN(size);
-	addr_t lastAddress = address + (size - 1);
 
 	// Check, whether the caller is allowed to modify the concerned areas.
 	if (!kernel) {
-		for (VMAddressSpace::AreaIterator it = addressSpace->GetAreaIterator();
+		for (VMAddressSpace::AreaRangeIterator it
+				= addressSpace->GetAreaRangeIterator(address, size);
 			VMArea* area = it.Next();) {
-			addr_t areaLast = area->Base() + (area->Size() - 1);
+
-			if (area->Base() < lastAddress && address < areaLast) {
 			if ((area->protection & B_KERNEL_AREA) != 0) {
 				dprintf("unmap_address_range: team %" B_PRId32 " tried to "
 					"unmap range of kernel area %" B_PRId32 " (%s)\n",
@@ -849,10 +848,11 @@ unmap_address_range(VMAddressSpace* addressSpace, addr_t address, addr_t size,
 			}
 		}
 	}
-	}
 
-	for (VMAddressSpace::AreaIterator it = addressSpace->GetAreaIterator();
+	for (VMAddressSpace::AreaRangeIterator it
+			= addressSpace->GetAreaRangeIterator(address, size);
 		VMArea* area = it.Next();) {
+
 		status_t error = cut_area(addressSpace, area, address, size, NULL,
 			kernel);
 		if (error != B_OK)
@@ -1092,15 +1092,9 @@ static inline bool
 wait_if_address_range_is_wired(VMAddressSpace* addressSpace, addr_t base,
 	size_t size, LockerType* locker)
 {
-	addr_t end = base + size - 1;
+	for (VMAddressSpace::AreaRangeIterator it
-	for (VMAddressSpace::AreaIterator it = addressSpace->GetAreaIterator();
+		= addressSpace->GetAreaRangeIterator(base, size);
 			VMArea* area = it.Next();) {
-		// TODO: Introduce a VMAddressSpace method to get a close iterator!
-		if (area->Base() > end)
-			return false;
-
-		if (base >= area->Base() + area->Size() - 1)
-			continue;
 
 		AreaCacheLocker cacheLocker(vm_area_get_locked_cache(area));