kernel/vm: Remove linear search from _get_next_area_info.

This introduces VMAddressSpace::FindClosestArea() that can be used to
find the closest area to a given address in either direction. This is
now trivial and efficient since both kernel and user address spaces use
a binary search tree.

Using FindClosestArea() getting multiple area infos is sped up
dramatically as it removes the need for a linear search from the first
area to the one given in the cookie on each successive invocation.

Change-Id: I227da87d915f6f3d3ef88bfeb6be5d4c97c3baaa
Reviewed-on: https://review.haiku-os.org/c/haiku/+/2840
Reviewed-by: waddlesplash <[email protected]>

headers/private/kernel/vm/VMAddressSpace.h

@@ -76,6 +76,8 @@ public:
 	virtual	VMArea*				NextArea(VMArea* area) const = 0;
 
 	virtual	VMArea*				LookupArea(addr_t address) const = 0;
+	virtual	VMArea*				FindClosestArea(addr_t address, bool less) const
+									= 0;
 	virtual	VMArea*				CreateArea(const char* name, uint32 wiring,
 									uint32 protection,
 									uint32 allocationFlags) = 0;

src/system/kernel/vm/VMKernelAddressSpace.cpp

@@ -171,6 +171,18 @@ VMKernelAddressSpace::LookupArea(addr_t address) const
 }
 
 
+//! You must hold the address space's read lock.
+VMArea*
+VMKernelAddressSpace::FindClosestArea(addr_t address, bool less) const
+{
+	Range* range = fRangeTree.FindClosest(address, less);
+	while (range != NULL && range->type != Range::RANGE_AREA)
+		range = fRangeTree.Next(range);
+
+	return range != NULL ? range->area : NULL;
+}
+
+
 /*!	This inserts the area you pass into the address space.
 	It will also set the "_address" argument to its base address when
 	the call succeeds.

src/system/kernel/vm/VMKernelAddressSpace.h

@@ -26,6 +26,8 @@ public:
 	virtual	VMArea*				NextArea(VMArea* area) const;
 
 	virtual	VMArea*				LookupArea(addr_t address) const;
+	virtual	VMArea*				FindClosestArea(addr_t address, bool less)
+									const;
 	virtual	VMArea*				CreateArea(const char* name, uint32 wiring,
 									uint32 protection, uint32 allocationFlags);
 	virtual	void				DeleteArea(VMArea* area,

src/system/kernel/vm/VMUserAddressSpace.cpp

@@ -142,6 +142,17 @@ VMUserAddressSpace::LookupArea(addr_t address) const
 }
 
 
+//! You must hold the address space's read lock.
+VMArea*
+VMUserAddressSpace::FindClosestArea(addr_t address, bool less) const
+{
+	VMUserArea* area = fAreas.FindClosest(address, less);
+	while (area != NULL && area->id == RESERVED_AREA_ID)
+		area = fAreas.Next(area);
+	return area;
+}
+
+
 /*!	This inserts the area you pass into the address space.
 	It will also set the "_address" argument to its base address when
 	the call succeeds.

src/system/kernel/vm/VMUserAddressSpace.h

@@ -21,6 +21,8 @@ public:
 	virtual	VMArea*				NextArea(VMArea* area) const;
 
 	virtual	VMArea*				LookupArea(addr_t address) const;
+	virtual	VMArea*				FindClosestArea(addr_t address, bool less)
+									const;
 	virtual	VMArea*				CreateArea(const char* name, uint32 wiring,
 									uint32 protection, uint32 allocationFlags);
 	virtual	void				DeleteArea(VMArea* area,

src/system/kernel/vm/vm.cpp

@@ -6050,21 +6050,14 @@ _get_next_area_info(team_id team, ssize_t* cookie, area_info* info, size_t size)
 	if (!locker.IsLocked())
 		return B_BAD_TEAM_ID;
 
-	VMArea* area;
+	VMArea* area = locker.AddressSpace()->FindClosestArea(nextBase, false);
-	for (VMAddressSpace::AreaIterator it
-				= locker.AddressSpace()->GetAreaIterator();
-			(area = it.Next()) != NULL;) {
-		if (area->Base() > nextBase)
-			break;
-	}
-
 	if (area == NULL) {
 		nextBase = (addr_t)-1;
 		return B_ENTRY_NOT_FOUND;
 	}
 
 	fill_area_info(area, info, size);
-	*cookie = (ssize_t)(area->Base());
+	*cookie = (ssize_t)(area->Base() + 1);
 
 	return B_OK;
 }