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