diff --git a/src/io/io.cpp b/src/io/io.cpp
index e8b9ce337..e413b2799 100644
--- a/src/io/io.cpp
+++ b/src/io/io.cpp
@@ -37,8 +37,7 @@ DataMatrix* LoadDataMatrix(const char *fname, bool silent, bool savebuffer) {
 }
 
 void SaveDataMatrix(const DataMatrix &dmat, const char *fname, bool silent) {
-  if (!strcmp(fname + strlen(fname) - 5, ".page")) {
-    
+  if (!strcmp(fname + strlen(fname) - 5, ".page")) {    
     DMatrixPage::Save(fname, dmat, silent);
     return;
   }
@@ -46,7 +45,9 @@ void SaveDataMatrix(const DataMatrix &dmat, const char *fname, bool silent) {
     const DMatrixSimple *p_dmat = static_cast<const DMatrixSimple*>(&dmat);
     p_dmat->SaveBinary(fname, silent);
   } else {
-    utils::Error("not implemented");
+    DMatrixSimple smat;
+    smat.CopyFrom(dmat);
+    smat.SaveBinary(fname, silent);
   }
 }
 
diff --git a/src/io/page_dmatrix-inl.hpp b/src/io/page_dmatrix-inl.hpp
index 4d13a0bc5..2701fb3b3 100644
--- a/src/io/page_dmatrix-inl.hpp
+++ b/src/io/page_dmatrix-inl.hpp
@@ -32,7 +32,7 @@ struct RowBatchPage {
     const size_t dsize = row.length * sizeof(RowBatch::Entry);
     if (FreeBytes() < dsize+ sizeof(int)) return false;
     row_ptr(Size() + 1) = row_ptr(Size()) + row.length;    
-    memcpy(data_ptr(Size()) , row.data, dsize);
+    memcpy(data_ptr(row_ptr(Size())) , row.data, dsize);
     ++ data_[0];
     return true;    
   }
@@ -48,13 +48,18 @@ struct RowBatchPage {
     batch.data_ptr = this->data_ptr(0);
     batch.size = static_cast<size_t>(this->Size());
     std::vector<size_t> &rptr = *p_rptr;
-    rptr.resize(this->Size()+1);
+    rptr.resize(this->Size() + 1);
     for (size_t i = 0; i < rptr.size(); ++i) {
       rptr[i] = static_cast<size_t>(this->row_ptr(i));
     }
     batch.ind_ptr = &rptr[0];
     return batch;
   }
+  /*! \brief get i-th row from the batch */
+  inline RowBatch::Inst operator[](size_t i) {
+    return RowBatch::Inst(data_ptr(0) + row_ptr(i), 
+                          static_cast<bst_uint>(row_ptr(i+1) - row_ptr(i)));
+  }
   /*!
    * \brief clear the page, cleanup the content
    */
@@ -77,7 +82,7 @@ struct RowBatchPage {
     return data_[0];
   }
   /*! \brief page size 64 MB */
-  static const size_t kPageSize = 64 << 18;
+  static const size_t kPageSize = 64 << 8;
 
  private:
   /*! \return number of elements */
@@ -112,7 +117,6 @@ class ThreadRowPageIterator: public utils::IIterator<RowBatch> {
     itr.BeforeFirst();
     isend_ = false;
     base_rowid_ = 0;
-    utils::Assert(this->LoadNextPage(), "ThreadRowPageIterator");
   }
   virtual bool Next(void) {
     if(!this->LoadNextPage()) return false;
diff --git a/src/io/simple_dmatrix-inl.hpp b/src/io/simple_dmatrix-inl.hpp
index 47be8a41a..8d7064bdd 100644
--- a/src/io/simple_dmatrix-inl.hpp
+++ b/src/io/simple_dmatrix-inl.hpp
@@ -44,8 +44,8 @@ class DMatrixSimple : public DataMatrix {
   }
   /*! \brief copy content data from source matrix */
   inline void CopyFrom(const DataMatrix &src) {
-    this->info = src.info;
     this->Clear();
+    this->info = src.info;
     // clone data content in thos matrix
     utils::IIterator<RowBatch> *iter = src.fmat()->RowIterator();
     iter->BeforeFirst();
diff --git a/src/io/simple_fmatrix-inl.hpp b/src/io/simple_fmatrix-inl.hpp
index 86763a105..f099eb1a9 100644
--- a/src/io/simple_fmatrix-inl.hpp
+++ b/src/io/simple_fmatrix-inl.hpp
@@ -150,7 +150,7 @@ class FMatrixS : public IFMatrix{
     iter_->BeforeFirst();
     while (iter_->Next()) {
       const RowBatch &batch = iter_->Value();
-      for (size_t i = 0; i < batch.size; ++i) {
+      for (size_t i = 0; i < batch.size; ++i) {        
         if (pkeep == 1.0f || random::SampleBinary(pkeep)) {
           buffered_rowset_.push_back(static_cast<bst_uint>(batch.base_rowid+i));
           RowBatch::Inst inst = batch[i];