diff --git a/xlib/avecl/__init__.py b/xlib/avecl/__init__.py
index 25455c1..e503228 100644
--- a/xlib/avecl/__init__.py
+++ b/xlib/avecl/__init__.py
@@ -7,6 +7,7 @@ Applicable for high-performance general purpose n-dim array computations for eve
 Works in python 3.5+. Dependencies: numpy.
 
 This lib uses relative import, thus you can place it in any subfolder.
+The lib is not thread-safe.
 
 made by @iperov from scratch.
 """
diff --git a/xlib/avecl/_internal/HKernel.py b/xlib/avecl/_internal/HKernel.py
index c6bbe76..b427c10 100644
--- a/xlib/avecl/_internal/HKernel.py
+++ b/xlib/avecl/_internal/HKernel.py
@@ -175,10 +175,7 @@ class HKernel:
         line = f'#define {name_upper}_IDX({HKernel.axes_seq_enum(name, ndim)}) '
 
         for i in range(ndim):
-            if i == 0:
-                line += f'( (size_t)({name_lower}{i}) )'
-            else:
-                line += f'( {name_lower}{i} )'
+            line += f'( (size_t)({name_lower}{i}) )'
 
             for j in range(i+1,ndim):
                 line += f'*{shape[j]} '
@@ -190,10 +187,7 @@ class HKernel:
         line = f'#define {name_upper}_IDX_MOD({HKernel.axes_seq_enum(name, ndim)}) '
 
         for i in range(ndim):
-            if i == 0:
-                line += f'( (size_t)({name_lower}{i}) % {shape[i]} )'
-            else:
-                line += f'( ({name_lower}{i}) % {shape[i]} )'
+            line += f'( (size_t)({name_lower}{i}) % {shape[i]} )'
 
             for j in range(i+1,ndim):
                 line += f'*{shape[j]} '
diff --git a/xlib/avecl/_internal/NCore.py b/xlib/avecl/_internal/NCore.py
index cd2597f..f4febec 100644
--- a/xlib/avecl/_internal/NCore.py
+++ b/xlib/avecl/_internal/NCore.py
@@ -15,10 +15,6 @@ class NCore:
         can raise Exception
         """
         SCacheton.cleanup()
-
-        if Tensor._object_count != 0:
-            raise Exception(f'Unable to cleanup while {Tensor._object_count} Tensor objects exist.')
-
         cleanup_devices()
 
 __all__ = ['NCore']
\ No newline at end of file
diff --git a/xlib/avecl/_internal/backend/Device.py b/xlib/avecl/_internal/backend/Device.py
index 9d439e9..544893a 100644
--- a/xlib/avecl/_internal/backend/Device.py
+++ b/xlib/avecl/_internal/backend/Device.py
@@ -1,3 +1,5 @@
+import random
+from collections import deque
 from typing import List, Union
 
 import numpy as np
@@ -38,6 +40,8 @@ class Device:
         self._ctx_q = None          # CL command queue
         self._ctx = None            # CL context
 
+        self._target_memory_usage = 0
+        
         self._total_memory_allocated = 0
         self._total_buffers_allocated = 0
         self._total_memory_pooled = 0
@@ -97,6 +101,9 @@ class Device:
         return self._cached_data.get(key, None)
 
     def get_total_allocated_memory(self):
+        """
+        get total bytes of used and pooled memory
+        """
         return self._total_memory_allocated
 
     def get_max_malloc_size(self) -> int:
@@ -153,6 +160,8 @@ class Device:
         return compiled_krn
 
     def _cl_mem_alloc(self, size) -> CL.cl_mem:
+        self._keep_target_memory_usage()
+        
         clr = CL.CLRESULT()
         mem = CL.clCreateBuffer(self._get_ctx(), CL.CL_MEM_READ_WRITE, size, None, clr)
         if clr == CL.CLERROR.SUCCESS:
@@ -172,6 +181,7 @@ class Device:
         if clr != CL.CLERROR.SUCCESS:
             raise Exception(f'clGetMemObjectInfo error: {clr}')
         size = size.value
+        
         self._total_memory_allocated -= size
         self._total_buffers_allocated -= 1
         clr = CL.clReleaseMemObject(mem)
@@ -182,12 +192,14 @@ class Device:
         """
         allocate or get cl_mem from pool
         """
+        self._keep_target_memory_usage()
+        
         pool = self._pooled_buffers
 
         # First try to get pooled buffer
         ar = pool.get(size, None)
         if ar is not None and len(ar) != 0:
-            mem = ar.pop(-1)
+            mem = ar.pop()
             self._total_memory_pooled -= size
             self._total_buffers_pooled -= 1
         else:
@@ -200,7 +212,7 @@ class Device:
                     for size_key in sorted(list(pool.keys()), reverse=True):
                         ar = pool[size_key]
                         if len(ar) != 0:
-                            buf_to_release = ar.pop(-1)
+                            buf_to_release = ar.pop()
                             break
 
                     if buf_to_release is not None:
@@ -208,8 +220,7 @@ class Device:
                         self._cl_mem_free(buf_to_release)
                         continue
 
-                    raise Exception(f'Unable to allocate {size // 1024**2}Mb on {str(self)}')
-
+                    raise Exception(f'Unable to allocate {size // 1024**2}Mb on {self.get_description()}')
 
                 break
 
@@ -228,7 +239,7 @@ class Device:
         pool = self._pooled_buffers
         ar = pool.get(size, None)
         if ar is None:
-            ar = pool[size] = []
+            ar = pool[size] = deque()
         ar.append(mem)
 
         self._total_memory_pooled += size
@@ -336,13 +347,33 @@ N of cacheddata:         {len(self._cached_data)}
         clr = CL.clFinish(self._get_ctx_q())
         if clr != CL.CLERROR.SUCCESS:
             raise Exception(f'clFinish error: {clr}')
-
-    def cleanup(self):
+    
+    def set_target_memory_usage(self, mb : int):
         """
-        Frees all resources from this Device.
+        keep memory usage at specified position
+        
+        when total allocated memory reached the target and new allocation is performing,        
+        random pooled memory will be freed
         """
-        self._cached_data = {}
-
+        self._target_memory_usage = mb*1024*1024
+    
+    def _keep_target_memory_usage(self):
+        targ = self._target_memory_usage
+        if targ != 0 and self.get_total_allocated_memory() >= targ:
+            # remove random 25% of pooled boofers
+            print('remove random 25% of pooled boofers')
+            pool = self._pooled_buffers            
+            mems = [ (k,x) for k in pool.keys() for x in pool[k]  ]            
+            for k, mem in random.sample(mems, max(1,int(len(mems)*0.25)) ):
+                self._cl_mem_free(mem)        
+                pool[k].remove(mem)
+                    
+        
+    def clear_pooled_memory(self):
+        """
+        frees pooled memory
+        """
+        
         pool = self._pooled_buffers
         for size_key in pool.keys():
             for mem in pool[size_key]:
@@ -350,6 +381,14 @@ N of cacheddata:         {len(self._cached_data)}
         self._pooled_buffers = {}
         self._total_memory_pooled = 0
         self._total_buffers_pooled = 0
+        
+    def cleanup(self):
+        """
+        Frees all resources from this Device.
+        """
+        self._cached_data = {}
+
+        self.clear_pooled_memory()
 
         if self._total_memory_allocated != 0:
             raise Exception('Unable to cleanup CLDevice, while not all Buffers are deallocated.')
@@ -459,7 +498,7 @@ def get_available_devices_info() -> List[DeviceInfo]:
 def get_default_device() -> Union[Device, None]:
     global _default_device
     if _default_device is None:
-        _default_device = get_device(0)
+        _default_device = get_best_device()
     return _default_device
 
 def set_default_device(device : Device):
@@ -473,7 +512,7 @@ def get_device(arg : Union[None, int, Device, DeviceInfo]) -> Union[Device, None
     """
     get physical TensorCL device.
 
-        arg     None        - get best device
+        arg     None        - get default device
                 int         - by index
                 DeviceInfo  - by device info
                 Device      - returns the same
@@ -481,7 +520,7 @@ def get_device(arg : Union[None, int, Device, DeviceInfo]) -> Union[Device, None
     global _devices
 
     if arg is None:
-        return get_best_device()
+        return get_default_device()
     elif isinstance(arg, int):
         devices_info = get_available_devices_info()
         if arg < len(devices_info):