diff --git a/paddle/memory/detail/system_allocator.cc b/paddle/memory/detail/system_allocator.cc
index 332ff062d47846505f91153d67cbaf2a6cdd7292..2b0fbfa87e22ad5697b1062d1d7b80f5eb251399 100644
--- a/paddle/memory/detail/system_allocator.cc
+++ b/paddle/memory/detail/system_allocator.cc
@@ -39,22 +39,22 @@ void* CPUAllocator::Alloc(size_t& index, size_t size) {
   // pointer shall not be dereferenced -- so we make it nullptr.
   if (size <= 0) return nullptr;
 
-  if (FLAGS_use_pinned_memory) {
-    void* p = malloc(size);
-    if (p != nullptr) {
-      mlock(p, size);
-    }
-  }
+  index = 0;  // unlock memory
 
   void* p = malloc(size);
-  if (p != nullptr && FLAGS_use_pinned_memory) {
-    mlock(p, size);
+
+  if (p != nullptr) {
+    if (FLAGS_use_pinned_memory) {
+      index = 1;
+      mlock(p, size);  // lock memory
+    }
   }
+
   return p;
 }
 
 void CPUAllocator::Free(void* p, size_t size, size_t index) {
-  if (p != nullptr && FLAGS_use_pinned_memory) {
+  if (p != nullptr && index == 1) {
     munlock(p, size);
   }
   free(p);
@@ -73,26 +73,34 @@ void* GPUAllocator::Alloc(size_t& index, size_t size) {
 
   // Reserve memory for page tables, etc.
   size_t reserving = capacity - paddle::platform::GpuMaxAllocSize();
-  size_t remaining = available > reserving ? available - reserving : 0;
+  size_t usable = available > reserving ? available - reserving : 0;
 
   // If remaining size no less than expected size, using general
   // cudaMalloc to allocate GPU memory.
   void* p = 0;
-  if (size <= remaining) {
+  if (size <= usable) {
     cudaError_t result = cudaMalloc(&p, size);
     if (result == cudaSuccess) {
       index = 0;
-      total_alloc_size_ += size;
+      gpu_alloc_size_ += size;
       return p;
     }
   }
 
   // If remaining size less than expected size or cudaMalloc failed,
   // cudaMallocHost will be considered as a fallback allocator.
+  //
+  // NOTE: here, we use GpuMaxAllocSize() as the maximum memory size
+  // of host fallback allocation. Allocates too much would reduce
+  // the amount of memory available to the underlying system for paging.
+  usable = paddle::platform::GpuMaxAllocSize() - fallback_alloc_size_;
+
+  if (size > usable) return nullptr;
+
   cudaError_t result = cudaMallocHost(&p, size);
   if (result == cudaSuccess) {
     index = 1;
-    total_alloc_size_ += size;
+    fallback_alloc_size_ += size;
     return p;
   }
 
@@ -100,16 +108,26 @@ void* GPUAllocator::Alloc(size_t& index, size_t size) {
 }
 
 void GPUAllocator::Free(void* p, size_t size, size_t index) {
+  cudaError_t err;
+
+  if (index == 0) {
+    PADDLE_ASSERT(gpu_alloc_size_ >= size);
+    gpu_alloc_size_ -= size;
+    err = cudaFree(p);
+  } else {
+    PADDLE_ASSERT(fallback_alloc_size_ >= size);
+    fallback_alloc_size_ -= size;
+    err = cudaFreeHost(p);
+  }
+
   // Purposefully allow cudaErrorCudartUnloading, because
   // that is returned if you ever call cudaFree after the
   // driver has already shutdown. This happens only if the
   // process is terminating, in which case we don't care if
   // cudaFree succeeds.
-  PADDLE_ASSERT(total_alloc_size_ >= size);
-  total_alloc_size_ -= size;
-  cudaError_t err = index == 1 ? cudaFreeHost(p) : cudaFree(p);
   if (err != cudaErrorCudartUnloading) {
-    platform::throw_on_error(err, "cudaFree{Host} failed");
+    platform::throw_on_error(err,
+                             "cudaFree{Host} failed in GPUAllocator::Free.");
   }
 }
 
diff --git a/paddle/memory/detail/system_allocator.h b/paddle/memory/detail/system_allocator.h
index e15302ce4f0ae106c2beb0d07dfc911b8ad00187..7093c42967162c6737e1fe68176cf3993a18ba09 100644
--- a/paddle/memory/detail/system_allocator.h
+++ b/paddle/memory/detail/system_allocator.h
@@ -47,7 +47,8 @@ class GPUAllocator : public SystemAllocator {
   virtual void Free(void* p, size_t size, size_t index);
 
  private:
-  size_t total_alloc_size_ = 0;
+  size_t gpu_alloc_size_ = 0;
+  size_t fallback_alloc_size_ = 0;
 };
 #endif  // PADDLE_ONLY_CPU
 
diff --git a/python/paddle/trainer_config_helpers/networks.py b/python/paddle/trainer_config_helpers/networks.py
index 67154a8d7d366bd983b4426da87e0b33307fced4..1bf59ed4840ae69afc5bce49c86a08b60e9603ee 100755
--- a/python/paddle/trainer_config_helpers/networks.py
+++ b/python/paddle/trainer_config_helpers/networks.py
@@ -1381,7 +1381,7 @@ def inputs(layers, *args):
     if len(args) != 0:
         layers.extend(args)
 
-    Inputs(* [l.name for l in layers])
+    Inputs(*[l.name for l in layers])
 
 
 def outputs(layers, *args):
@@ -1424,7 +1424,7 @@ def outputs(layers, *args):
     assert len(layers) > 0
 
     if HasInputsSet():  # input already set
-        Outputs(* [l.name for l in layers])
+        Outputs(*[l.name for l in layers])
         return  # just return outputs.
 
     if len(layers) != 1: