diff --git a/src/io/dmlc_simple.cpp b/src/io/dmlc_simple.cpp
index 4296d5caa..3138dae94 100644
--- a/src/io/dmlc_simple.cpp
+++ b/src/io/dmlc_simple.cpp
@@ -8,45 +8,132 @@
 
 namespace xgboost {
 namespace utils {
+/*!
+ * \brief line split implementation from single FILE 
+ * simply returns lines of files, used for stdin
+ */
 class SingleFileSplit : public dmlc::InputSplit {
  public:
-  explicit SingleFileSplit(const char *fname) 
-      : use_stdin_(false) {
+  explicit SingleFileSplit(const char *fname)
+      : use_stdin_(false),
+        chunk_begin_(NULL), chunk_end_(NULL) {
     if (!std::strcmp(fname, "stdin")) {
 #ifndef XGBOOST_STRICT_CXX98_
       use_stdin_ = true; fp_ = stdin;
 #endif
     }
     if (!use_stdin_) {
-      fp_ = utils::FopenCheck(fname, "r");
+      fp_ = utils::FopenCheck(fname, "rb");
     }
-    end_of_file_ = false;
+    buffer_.resize(kBufferSize);
   }
   virtual ~SingleFileSplit(void) {
     if (!use_stdin_) std::fclose(fp_);
   }
-  virtual bool ReadRecord(std::string *out_data) {
-    if (end_of_file_) return false;
-    out_data->clear();
-    while (true) {
-      char c = std::fgetc(fp_);
-      if (c == EOF) {
-        end_of_file_ = true;
+  virtual size_t Read(void *ptr, size_t size) {
+    return std::fread(ptr, 1, size, fp_);
+  }  
+  virtual void Write(const void *ptr, size_t size) {
+    utils::Error("cannot do write in inputsplit");
+  }
+  virtual bool NextRecord(Blob *out_rec) {
+    if (chunk_begin_ == chunk_end_) {
+      if (!LoadChunk()) return false;
+    }
+    char *next = FindNextRecord(chunk_begin_,
+                                chunk_end_);
+    out_rec->dptr = chunk_begin_;
+    out_rec->size = next - chunk_begin_;
+    chunk_begin_ = next;    
+    return true;
+  }
+  virtual bool NextChunk(Blob *out_chunk) {
+    if (chunk_begin_ == chunk_end_) {
+      if (!LoadChunk()) return false;
+    }    
+    out_chunk->dptr = chunk_begin_;
+    out_chunk->size = chunk_end_ - chunk_begin_;
+    chunk_begin_ = chunk_end_;
+    return true;
+  }
+  inline bool ReadChunk(void *buf, size_t *size) {
+    size_t max_size = *size;
+    if (max_size <= overflow_.length()) {
+      *size = 0; return true;
+    }
+    if (overflow_.length() != 0) { 
+      std::memcpy(buf, BeginPtr(overflow_), overflow_.length());  
+    }
+    size_t olen = overflow_.length();
+    overflow_.resize(0);
+    size_t nread = this->Read(reinterpret_cast<char*>(buf) + olen,
+                              max_size - olen);
+    nread += olen;
+    if (nread == 0) return false;
+    if (nread != max_size) {
+      *size = nread;
+      return true;
+    } else {
+      const char *bptr = reinterpret_cast<const char*>(buf);
+      // return the last position where a record starts
+      const char *bend = this->FindLastRecordBegin(bptr, bptr + max_size);
+      *size = bend - bptr;
+      overflow_.resize(max_size - *size);
+      if (overflow_.length() != 0) {
+        std::memcpy(BeginPtr(overflow_), bend, overflow_.length());
       }
-      if (c != '\r' && c != '\n' && c != EOF) {
-        *out_data += c;
+      return true;
+    }
+  }
+  
+ protected:
+  inline const char* FindLastRecordBegin(const char *begin,
+                                         const char *end) {
+    if (begin == end) return begin;
+    for (const char *p = end - 1; p != begin; --p) {
+      if (*p == '\n' || *p == '\r') return p + 1; 
+    }
+    return begin;
+  }
+  inline char* FindNextRecord(char *begin, char *end) {
+    char *p;
+    for (p = begin; p != end; ++p) {
+      if (*p == '\n' || *p == '\r') break;
+    }
+    for (; p != end; ++p) {
+      if (*p != '\n' && *p != '\r') return p;
+    }
+    return end;
+  }
+  inline bool LoadChunk(void) {
+    while (true) {
+      size_t size = buffer_.length();
+      if (!ReadChunk(BeginPtr(buffer_), &size)) return false;
+      if (size == 0) {
+        buffer_.resize(buffer_.length() * 2);
       } else {
-        if (out_data->length() != 0) return true;
-        if (end_of_file_) return false;
+        chunk_begin_ = reinterpret_cast<char *>(BeginPtr(buffer_));
+        chunk_end_ = chunk_begin_ + size;
+        break;
       }
     }
-    return false;
-  }  
-    
+    return true;
+  }
+
  private:
+  // buffer size
+  static const size_t kBufferSize = 1 << 18UL;
+  // file
   std::FILE *fp_;
   bool use_stdin_;
-  bool end_of_file_;
+  // internal overflow
+  std::string overflow_;
+  // internal buffer
+  std::string buffer_;
+  // beginning of chunk
+  char *chunk_begin_;
+  // end of chunk
+  char *chunk_end_;
 };
 
 class StdFile : public dmlc::Stream {
@@ -105,7 +192,8 @@ class StdFile : public dmlc::Stream {
 namespace dmlc {
 InputSplit* InputSplit::Create(const char *uri,
                                unsigned part,
-                               unsigned nsplit) {
+                               unsigned nsplit,
+                               const char *type) {
   using namespace xgboost;
   const char *msg = "xgboost is compiled in local mode\n"\
       "to use hdfs, s3 or distributed version, compile with make dmlc=1";
diff --git a/src/io/libsvm_parser.h b/src/io/libsvm_parser.h
new file mode 100644
index 000000000..6767d61be
--- /dev/null
+++ b/src/io/libsvm_parser.h
@@ -0,0 +1,168 @@
+/*!
+ *  Copyright (c) 2015 by Contributors
+ * \file libsvm_parser.h
+ * \brief iterator parser to parse libsvm format
+ * \author Tianqi Chen
+ */
+#ifndef XGBOOST_IO_LIBSVM_PARSER_H_
+#define XGBOOST_IO_LIBSVM_PARSER_H_
+
+#include <vector>
+#include <cstring>
+#include <cctype>
+#include "../utils/omp.h"
+#include "../utils/utils.h"
+#include "../sync/sync.h"
+#include "./sparse_batch_page.h"
+
+namespace xgboost {
+namespace io {
+/*! \brief page returned by libsvm parser */
+struct LibSVMPage : public SparsePage {
+  std::vector<float> label;
+  // overload clear  
+  inline void Clear() {
+    SparsePage::Clear();
+    label.clear();
+  }
+};
+/*!
+ * \brief libsvm parser that parses the input lines
+ * and returns rows in input data
+ */
+class LibSVMParser : public utils::IIterator<LibSVMPage> {
+ public:
+  explicit LibSVMParser(dmlc::InputSplit *source,
+                        int nthread)
+      : bytes_read_(0), at_head_(true),
+        data_ptr_(0), data_end_(0), source_(source) {
+    int maxthread;
+    #pragma omp parallel
+    {
+      maxthread = omp_get_num_threads();
+    }
+    maxthread = std::max(maxthread / 2, 1);
+    nthread_ = std::min(maxthread, nthread);
+  }
+  virtual ~LibSVMParser() {
+    delete source_;
+  }
+  virtual void BeforeFirst(void) {
+    utils::Assert(at_head_, "cannot call BeforeFirst");
+  }
+  virtual const LibSVMPage &Value(void) const {
+    return data_[data_ptr_ - 1];
+  }
+  virtual bool Next(void) {
+    while (true) {
+      while (data_ptr_ < data_end_) {
+        data_ptr_ += 1;
+        if (data_[data_ptr_ - 1].Size() != 0) {
+          return true;
+        }
+      }
+      if (!FillData()) break;
+      data_ptr_ = 0; data_end_ = data_.size();
+    }
+    return false;
+  }
+  inline size_t bytes_read(void) const {
+    return bytes_read_;
+  }
+
+ protected:
+  inline bool FillData() {
+    dmlc::InputSplit::Blob chunk;
+    if (!source_->NextChunk(&chunk)) return false;
+    int nthread;
+    #pragma omp parallel num_threads(nthread_)
+    {
+      nthread = omp_get_num_threads();
+    }
+    // reserve space for data
+    data_.resize(nthread);
+    bytes_read_ += chunk.size;
+    utils::Assert(chunk.size != 0, "LibSVMParser.FileData");
+    char *head = reinterpret_cast<char*>(chunk.dptr);        
+    #pragma omp parallel num_threads(nthread_)
+    {
+      // threadid
+      int tid = omp_get_thread_num();
+      size_t nstep = (chunk.size + nthread - 1) / nthread;
+      size_t sbegin = std::min(tid * nstep, chunk.size);
+      size_t send = std::min((tid + 1) * nstep, chunk.size);
+      char *pbegin = BackFindEndLine(head + sbegin, head);
+      char *pend;
+      if (tid + 1 == nthread) {
+        pend = head + send;
+      } else {
+        pend = BackFindEndLine(head + send, head);
+      }
+      ParseBlock(pbegin, pend, &data_[tid]);
+    }
+    data_ptr_ = 0;
+    return true;
+  }
+  /*!
+   * \brief parse data into out
+   * \param begin beginning of buffer
+   * \param end end of buffer
+   */
+  inline void ParseBlock(char *begin,
+                         char *end,
+                         LibSVMPage *out) {    
+    out->Clear();
+    char *p = begin;
+    while (p != end) {
+      while (isspace(*p) && p != end) ++p;
+      if (p == end) break;
+      char *head = p;
+      while (isdigit(*p) && p != end) ++p;
+      if (*p == ':') {
+        out->data.push_back(SparseBatch::Entry(atol(head),
+                                               atof(p + 1)));
+      } else {
+        if (out->label.size() != 0) {
+          out->offset.push_back(out->data.size());
+        }
+        out->label.push_back(atof(head));
+      }
+      while (!isspace(*p) && p != end) ++p;
+    }
+    if (out->label.size() != 0) {
+      out->offset.push_back(out->data.size());
+    }
+    utils::Check(out->label.size() + 1 == out->offset.size(),
+                 "LibSVMParser inconsistent");
+  }
+  /*!
+   * \brief start from bptr, go backward and find first endof line
+   * \param bptr end position to go backward
+   * \param begin the beginning position of buffer
+   * \return position of first endof line going backward
+   */
+  inline char* BackFindEndLine(char *bptr,
+                               char *begin) {
+    for (; bptr != begin; --bptr) {
+      if (*bptr == '\n' || *bptr == '\r') return bptr;
+    }
+    return begin;
+  }
+  
+ private:
+  // nthread
+  int nthread_;
+  // number of bytes readed
+  size_t bytes_read_;
+  // at beginning, at end of stream
+  bool at_head_;
+  // pointer to begin and end of data
+  size_t data_ptr_, data_end_;
+  // source split that provides the data
+  dmlc::InputSplit *source_;
+  // internal data
+  std::vector<LibSVMPage> data_;
+};
+}  // namespace io
+}  // namespace xgboost
+#endif  // XGBOOST_IO_LIBSVM_PARSER_H_
diff --git a/src/io/page_dmatrix-inl.hpp b/src/io/page_dmatrix-inl.hpp
index 03f0d5ca8..047d589a1 100644
--- a/src/io/page_dmatrix-inl.hpp
+++ b/src/io/page_dmatrix-inl.hpp
@@ -12,6 +12,7 @@
 #include "./simple_fmatrix-inl.hpp"
 #include "./sparse_batch_page.h"
 #include "./page_fmatrix-inl.hpp"
+#include "./libsvm_parser.h"
 
 namespace xgboost {
 namespace io {
@@ -143,38 +144,32 @@ class DMatrixPageBase : public DataMatrix {
     std::string fname_row = std::string(cache_file) + ".row.blob";
     utils::FileStream fo(utils::FopenCheck(fname_row.c_str(), "wb"));    
     SparsePage page;
-    dmlc::InputSplit *in =
-        dmlc::InputSplit::Create(uri, rank, npart);
-    std::string line;
+    
+    LibSVMParser parser(
+        dmlc::InputSplit::Create(uri, rank, npart, "text"), 4);
     info.Clear();
-    while (in->ReadRecord(&line)) {
-      float label;
-      std::istringstream ss(line);
-      std::vector<RowBatch::Entry> feats;
-      ss >> label;
-      while (!ss.eof()) {
-        RowBatch::Entry e;
-        if (!(ss >> e.index)) break;
-        ss.ignore(32, ':');
-        if (!(ss >> e.fvalue)) break;
-        feats.push_back(e);
+    while (parser.Next()) {
+      const LibSVMPage &batch = parser.Value();
+      size_t nlabel = info.labels.size();
+      info.labels.resize(nlabel + batch.label.size());
+      if (batch.label.size() != 0) {
+        std::memcpy(BeginPtr(info.labels) + nlabel,
+                    BeginPtr(batch.label),
+                    batch.label.size() * sizeof(float));
+      }      
+      page.Push(batch);
+      for (size_t i = 0; i < batch.data.size(); ++i) {
+        info.info.num_col = std::max(info.info.num_col,
+                                     static_cast<size_t>(batch.data[i].index+1));
       }
-      RowBatch::Inst row(BeginPtr(feats), feats.size());
-      page.Push(row);
       if (page.MemCostBytes() >= kPageSize) {
         page.Save(&fo); page.Clear();
       }
-      for (size_t i = 0; i < feats.size(); ++i) {
-        info.info.num_col = std::max(info.info.num_col,
-                                     static_cast<size_t>(feats[i].index+1));
-      }
-      this->info.labels.push_back(label);
-      info.info.num_row += 1;
+      info.info.num_row += batch.label.size();
     }
     if (page.data.size() != 0) {
       page.Save(&fo);
     }
-    delete in;
     fo.Close();    
     iter_->Load(utils::FileStream(utils::FopenCheck(fname_row.c_str(), "rb")));    
     // save data matrix
diff --git a/src/io/simple_dmatrix-inl.hpp b/src/io/simple_dmatrix-inl.hpp
index e0ea7899e..010bf9893 100644
--- a/src/io/simple_dmatrix-inl.hpp
+++ b/src/io/simple_dmatrix-inl.hpp
@@ -19,6 +19,7 @@
 #include "./io.h"
 #include "./simple_fmatrix-inl.hpp"
 #include "../sync/sync.h"
+#include "./libsvm_parser.h"
 
 namespace xgboost {
 namespace io {
@@ -72,7 +73,8 @@ class DMatrixSimple : public DataMatrix {
   inline size_t AddRow(const std::vector<RowBatch::Entry> &feats) {
     for (size_t i = 0; i < feats.size(); ++i) {
       row_data_.push_back(feats[i]);
-      info.info.num_col = std::max(info.info.num_col, static_cast<size_t>(feats[i].index+1));
+      info.info.num_col = std::max(info.info.num_col,
+                                   static_cast<size_t>(feats[i].index+1));
     }
     row_ptr_.push_back(row_ptr_.back() + feats.size());
     info.info.num_row += 1;
@@ -90,26 +92,35 @@ class DMatrixSimple : public DataMatrix {
       rank = rabit::GetRank();
       npart = rabit::GetWorldSize();
     }
-    dmlc::InputSplit *in =
-        dmlc::InputSplit::Create(uri, rank, npart);
+    LibSVMParser parser(
+        dmlc::InputSplit::Create(uri, rank, npart, "text"), 4);
     this->Clear();
-    std::string line;
-    while (in->ReadRecord(&line)) {
-      float label;
-      std::istringstream ss(line);
-      std::vector<RowBatch::Entry> feats;
-      ss >> label;
-      while (!ss.eof()) {
-        RowBatch::Entry e;
-        if (!(ss >> e.index)) break;
-        ss.ignore(32, ':');
-        if (!(ss >> e.fvalue)) break;
-        feats.push_back(e);
+    while (parser.Next()) {
+      const LibSVMPage &batch = parser.Value();
+      size_t nlabel = info.labels.size();
+      info.labels.resize(nlabel + batch.label.size());
+      if (batch.label.size() != 0) {
+        std::memcpy(BeginPtr(info.labels) + nlabel,
+                    BeginPtr(batch.label),
+                    batch.label.size() * sizeof(float));
       }
-      info.labels.push_back(label);
-      this->AddRow(feats);
+      size_t ndata = row_data_.size();
+      row_data_.resize(ndata + batch.data.size());
+      if (batch.data.size() != 0) {
+        std::memcpy(BeginPtr(row_data_) + ndata,
+                    BeginPtr(batch.data),
+                    batch.data.size() * sizeof(RowBatch::Entry));
+      }
+      row_ptr_.resize(row_ptr_.size() + batch.label.size());
+      for (size_t i = 0; i < batch.label.size(); ++i) {
+        row_ptr_[nlabel + i + 1] = row_ptr_[nlabel] + batch.offset[i + 1];
+      }
+      info.info.num_row += batch.Size();
+      for (size_t i = 0; i < batch.data.size(); ++i) {
+        info.info.num_col = std::max(info.info.num_col,
+                                     static_cast<size_t>(batch.data[i].index+1));
+      }      
     }
-    delete in;
     if (!silent) {
       utils::Printf("%lux%lu matrix with %lu entries is loaded from %s\n",
                     static_cast<unsigned long>(info.num_row()),
diff --git a/src/io/sparse_batch_page.h b/src/io/sparse_batch_page.h
index 756bd1034..61155f380 100644
--- a/src/io/sparse_batch_page.h
+++ b/src/io/sparse_batch_page.h
@@ -150,7 +150,23 @@ class SparsePage {
     size_t begin = offset.size();
     offset.resize(offset.size() + batch.size);
     for (size_t i = 0; i < batch.size; ++i) {
-      offset[i + begin] = top + batch.ind_ptr[i] - batch.ind_ptr[0];
+      offset[i + begin] = top + batch.ind_ptr[i + 1] - batch.ind_ptr[0];
+    }
+  }
+  /*! 
+   * \brief Push a sparse page
+   * \param batch the row page
+   */
+  inline void Push(const SparsePage &batch) {
+    data.resize(offset.back() + batch.Size());
+    std::memcpy(BeginPtr(data) + offset.back(),
+                BeginPtr(batch.data),
+                sizeof(SparseBatch::Entry) * batch.data.size());
+    size_t top = offset.back();
+    size_t begin = offset.size();
+    offset.resize(offset.size() + batch.Size());
+    for (size_t i = 0; i < batch.Size(); ++i) {
+      offset[i + begin] = top + batch.offset[i + 1];
     }
   }
   /*! 
diff --git a/src/utils/utils.h b/src/utils/utils.h
index afe17f64c..7aee5a29a 100644
--- a/src/utils/utils.h
+++ b/src/utils/utils.h
@@ -174,5 +174,13 @@ inline const T *BeginPtr(const std::vector<T> &vec) {
     return &vec[0];
   }
 }
+inline char* BeginPtr(std::string &str) {
+  if (str.length() == 0) return NULL;
+  return &str[0];
+}
+inline const char* BeginPtr(const std::string &str) {
+  if (str.length() == 0) return NULL;
+  return &str[0];
+}
 }  // namespace xgboost
 #endif  // XGBOOST_UTILS_UTILS_H_