diff --git a/repos/ports/src/virtualbox/rt.cc b/repos/ports/src/virtualbox/rt.cc
index fdf2698779..ab52b09fa3 100644
--- a/repos/ports/src/virtualbox/rt.cc
+++ b/repos/ports/src/virtualbox/rt.cc
@@ -5,7 +5,7 @@
  */
 
 /*
- * Copyright (C) 2013 Genode Labs GmbH
+ * Copyright (C) 2013-2016 Genode Labs GmbH
  *
  * This file is distributed under the terms of the GNU General Public License
  * version 2.
@@ -16,6 +16,7 @@
 #include <base/env.h>
 #include <base/allocator_avl.h>
 
+
 /* VirtualBox includes */
 #include <iprt/initterm.h>
 #include <iprt/mem.h>
@@ -31,34 +32,183 @@ class Avl_ds : public Genode::Avl_node<Avl_ds>
 
 		Genode::Ram_dataspace_capability _ds;
 		Genode::addr_t _virt;
+		Genode::addr_t const _size;
+		Genode::addr_t _used_size;
+
+		bool _inuse = true;
+
+		static Genode::addr_t _mem_allocated;
+		static Genode::addr_t _mem_unused;
+
+		static Genode::Avl_tree<Avl_ds> _unused_ds;
+		static Genode::Avl_tree<Avl_ds> _runtime_ds;
 
 	public:
 
-		Avl_ds(Genode::Ram_dataspace_capability ds, void * virt)
-		: _ds(ds), _virt(reinterpret_cast<Genode::addr_t>(virt))
-		{ }
+		static Genode::addr_t hit;
+		static Genode::addr_t hit_coarse;
 
-		~Avl_ds() {
-			Genode::env()->ram_session()->free(_ds);
+		Avl_ds(Genode::Ram_dataspace_capability ds, void * virt,
+		       Genode::addr_t size)
+		:
+			_ds(ds), _virt(reinterpret_cast<Genode::addr_t>(virt)),
+			_size(size), _used_size(_size)
+		{
+			_mem_allocated += _size;
+			_runtime_ds.insert(this);
 		}
 
-		bool higher(Avl_ds *e) { return e->_virt > _virt; }
+		~Avl_ds() {
+			Assert (!_inuse);
 
-		Avl_ds *find(Genode::addr_t virt)
+			_unused_ds.remove(this);
+			_mem_unused -= _size;
+			_mem_allocated -= _size;
+
+			Genode::env()->ram_session()->free(_ds);
+			PWRN("free up %lu %lu/%lu hit=%lu/%lu avail=%zu",
+			     _size, _mem_allocated, _mem_unused, hit, hit_coarse,
+			     Genode::env()->ram_session()->avail());
+		}
+
+		void unused()
+		{
+			_inuse = false;
+
+			_runtime_ds.remove(this);
+
+			_mem_unused += _size;
+			_unused_ds.insert(this);
+		}
+
+		void used(Genode::addr_t size)
+		{
+			_inuse = true;
+
+			_unused_ds.remove(this);
+			_used_size = size;
+			_mem_unused -= _size;
+			_runtime_ds.insert(this);
+		}
+
+		bool higher(Avl_ds *e) {
+				return _inuse ? e->_virt > _virt : e->_size > _size; }
+
+		Avl_ds *find_virt(Genode::addr_t virt)
 		{
 			if (virt == _virt) return this;
 			Avl_ds *obj = this->child(virt > _virt);
-			return obj ? obj->find(virt) : 0;
+			return obj ? obj->find_virt(virt) : 0;
 		}
 
+		Avl_ds *find_coarse_match(Genode::addr_t size_min, Genode::addr_t size_max)
+		{
+			if (size_min <= _size && _size <= size_max) return this;
+			Avl_ds *obj = this->child(size_max > _size);
+			return obj ? obj->find_coarse_match(size_min, size_max) : 0;
+		}
+
+		Avl_ds *find_size(Genode::addr_t size, bool equal = true)
+		{
+			if (equal ? size == _size : size <= _size) return this;
+			Avl_ds *obj = this->child(size > _size);
+			return obj ? obj->find_size(size, equal) : 0;
+		}
+
+		static Avl_ds *find_match(Genode::addr_t size, bool coarse = false)
+		{
+			Avl_ds * head = _unused_ds.first();
+			if (!head)
+				return head;
+
+			return coarse ? head->find_coarse_match(size, size * 2)
+			              : head->find_size(size);
+		}
+
+		Genode::addr_t ds_virt() const { return _virt; }
+
+		static void memory_freeup(Genode::addr_t const cb)
+		{
+			/* free up memory if we hit some chosen limits */
+			enum {
+				MEMORY_MAX = 64 * 1024 * 1024,
+				MEMORY_CACHED = 16 * 1024 * 1024,
+			};
+
+			size_t cbx = cb * 4;
+			while (_unused_ds.first() && cbx &&
+			       (_mem_allocated + cb > MEMORY_MAX ||
+			        _mem_unused + cb > MEMORY_CACHED ||
+			        Genode::env()->ram_session()->avail() < cb * 2
+			       )
+			      )
+			{
+				Avl_ds * ds_free = _unused_ds.first()->find_size(cbx, false);
+				if (!ds_free) {
+					cbx = cbx / 2;
+					continue;
+				}
+
+				destroy(Genode::env()->heap(), ds_free);
+			}
+		}
+
+		static void free_memory(void * pv, size_t cb)
+		{
+			if (cb % 0x1000)
+				cb = (cb & ~0xFFFUL) + 0x1000UL;
+
+			Avl_ds * ds_obj = Avl_ds::_runtime_ds.first();
+			if (ds_obj)
+				ds_obj = ds_obj->find_virt(reinterpret_cast<Genode::addr_t>(pv));
+
+			if (ds_obj && ds_obj->_used_size == cb)
+				ds_obj->unused();
+			else {
+				PERR("%s unknown memory region %p(%lx)+%zx(%lx)",
+				     __func__, pv, ds_obj ? ds_obj->ds_virt() : 0,
+				     cb, ds_obj ? ds_obj->_size : 0);
+			}
+		}
 };
 
-static Genode::Avl_tree<Avl_ds> runtime_ds;
+Genode::Avl_tree<Avl_ds> Avl_ds::_runtime_ds;
+Genode::Avl_tree<Avl_ds> Avl_ds::_unused_ds;
+static Genode::Lock lock_ds;
+
+Genode::addr_t Avl_ds::hit = 0;
+Genode::addr_t Avl_ds::hit_coarse = 0;
+Genode::addr_t Avl_ds::_mem_allocated = 0;
+Genode::addr_t Avl_ds::_mem_unused = 0;
 
 static void *alloc_mem(size_t cb, const char *pszTag, bool executable = false)
 {
 	using namespace Genode;
 
+	if (!cb)
+		return nullptr;
+
+	if (cb % 0x1000)
+		cb = (cb & ~0xFFFUL) + 0x1000UL;
+
+	Lock::Guard guard(lock_ds);
+
+	if (Avl_ds * ds_free = Avl_ds::find_match(cb)) {
+		ds_free->used(cb);
+
+		Avl_ds::hit++;
+		return reinterpret_cast<void *>(ds_free->ds_virt());
+	} else
+	if (Avl_ds * ds_free = Avl_ds::find_match(cb, true)) {
+		ds_free->used(cb);
+
+		Avl_ds::hit_coarse++;
+		return reinterpret_cast<void *>(ds_free->ds_virt());
+	}
+
+	/* check for memory freeup, give hint about required memory (cb) */
+	Avl_ds::memory_freeup(cb);
+
 	try {
 		Ram_dataspace_capability ds = env()->ram_session()->alloc(cb);
 		Assert(ds.valid());
@@ -72,15 +222,13 @@ static void *alloc_mem(size_t cb, const char *pszTag, bool executable = false)
 		                                                any_addr, any_local_addr,
 		                                                executable);
 
-		if (!local_addr)
-			PERR("%s size=0x%zx, tag=%s -> %p", __func__, cb, pszTag, local_addr);
 		Assert(local_addr);
 
-		runtime_ds.insert(new (env()->heap()) Avl_ds(ds, local_addr));
+		new (env()->heap()) Avl_ds(ds, local_addr, cb);
 
 		return local_addr;
 	} catch (...) {
-		Assert(!"Could not allocate RTMem* memory ");
+		PERR("Could not allocate RTMem* memory of size=%zx", cb);
 		return nullptr;
 	}
 }
@@ -101,7 +249,10 @@ void *RTMemPageAllocZTag(size_t cb, const char *pszTag) RT_NO_THROW
 	 * The RAM dataspace freshly allocated by 'RTMemExecAllocTag' is zeroed
 	 * already.
 	 */
-	return alloc_mem(cb, pszTag);
+	void * addr = alloc_mem(cb, pszTag);
+	if (addr)
+		Genode::memset(addr, 0, cb);
+	return addr;
 }
 
 
@@ -113,17 +264,9 @@ void *RTMemPageAllocTag(size_t cb, const char *pszTag) RT_NO_THROW
 
 void RTMemPageFree(void *pv, size_t cb) RT_NO_THROW
 {
-	Avl_ds * ds_obj = runtime_ds.first();
-	if (ds_obj)
-		ds_obj = ds_obj->find(reinterpret_cast<Genode::addr_t>(pv));
-
-	if (ds_obj) {
-		runtime_ds.remove(ds_obj);
-		destroy(Genode::env()->heap(), ds_obj);
-	}
-	else
-		PERR("%s unknown memory region %p+%zx", __func__, pv, cb);
+	Genode::Lock::Guard guard(lock_ds);
 
+	Avl_ds::free_memory(pv, cb);
 }
 
 #include <iprt/buildconfig.h>