diff --git a/include/xgboost/data.h b/include/xgboost/data.h
index 9d954ae62..449c785b4 100644
--- a/include/xgboost/data.h
+++ b/include/xgboost/data.h
@@ -421,7 +421,7 @@ class BatchIterator {
     return *(*impl_);
   }
 
-  bool operator!=(const BatchIterator& rhs) const {
+  bool operator!=(const BatchIterator&) const {
     CHECK(impl_ != nullptr);
     return !impl_->AtEnd();
   }
diff --git a/include/xgboost/predictor.h b/include/xgboost/predictor.h
index 915fe0a9e..9e448c2f1 100644
--- a/include/xgboost/predictor.h
+++ b/include/xgboost/predictor.h
@@ -117,7 +117,7 @@ class Predictor {
    *
    * \param cfg   The configuration.
    */
-  virtual void Configure(const std::vector<std::pair<std::string, std::string>>& cfg);
+  virtual void Configure(const std::vector<std::pair<std::string, std::string>>&);
 
   /**
    * \brief Generate batch predictions for a given feature matrix. May use
diff --git a/src/c_api/c_api.cc b/src/c_api/c_api.cc
index d91b179f0..e562acbd3 100644
--- a/src/c_api/c_api.cc
+++ b/src/c_api/c_api.cc
@@ -163,7 +163,7 @@ XGB_DLL int XGDMatrixCreateFromCSCEx(const size_t* col_ptr,
                                      const unsigned* indices,
                                      const bst_float* data,
                                      size_t nindptr,
-                                     size_t nelem,
+                                     size_t,
                                      size_t num_row,
                                      DMatrixHandle* out) {
   API_BEGIN();
diff --git a/src/common/hist_util.cc b/src/common/hist_util.cc
index 01ed4bfc4..09a09897a 100644
--- a/src/common/hist_util.cc
+++ b/src/common/hist_util.cc
@@ -163,7 +163,7 @@ void GHistIndexMatrix::Init(DMatrix* p_fmat, int max_bins) {
     } else {
       common::Span<uint32_t> index_data_span = {index.data<uint32_t>(), n_index};
       SetIndexData(index_data_span, batch_threads, batch, rbegin, nbins,
-                   [](auto idx, auto i) { return idx; });
+                   [](auto idx, auto) { return idx; });
     }
 
     #pragma omp parallel for num_threads(nthread) schedule(static)
diff --git a/src/common/version.cc b/src/common/version.cc
index e9d4fe9d1..6f1af9fa6 100644
--- a/src/common/version.cc
+++ b/src/common/version.cc
@@ -16,7 +16,7 @@ namespace xgboost {
 
 const Version::TripletT Version::kInvalid {-1, -1, -1};
 
-Version::TripletT Version::Load(Json const& in, bool check) {
+Version::TripletT Version::Load(Json const& in) {
   if (get<Object const>(in).find("version") == get<Object const>(in).cend()) {
     return kInvalid;
   }
diff --git a/src/common/version.h b/src/common/version.h
index 96885f6a8..f143ed36a 100644
--- a/src/common/version.h
+++ b/src/common/version.h
@@ -18,7 +18,7 @@ struct Version {
   static const TripletT kInvalid;
 
   // Save/Load version info to Json document
-  static TripletT Load(Json const& in, bool check = false);
+  static TripletT Load(Json const& in);
   static void Save(Json* out);
 
   // Save/Load version info to dmlc::Stream
diff --git a/src/data/sparse_page_dmatrix.h b/src/data/sparse_page_dmatrix.h
index 393172658..00cbdbfbe 100644
--- a/src/data/sparse_page_dmatrix.h
+++ b/src/data/sparse_page_dmatrix.h
@@ -37,7 +37,7 @@ class SparsePageDMatrix : public DMatrix {
   const MetaInfo& Info() const override;
 
   bool SingleColBlock() const override { return false; }
-  DMatrix *Slice(common::Span<int32_t const> ridxs) override {
+  DMatrix *Slice(common::Span<int32_t const>) override {
     LOG(FATAL) << "Slicing DMatrix is not supported for external memory.";
     return nullptr;
   }
diff --git a/src/gbm/gblinear_model.h b/src/gbm/gblinear_model.h
index 6e3e83105..9f4888d82 100644
--- a/src/gbm/gblinear_model.h
+++ b/src/gbm/gblinear_model.h
@@ -49,7 +49,7 @@ class GBLinearModel : public Model {
  public:
   explicit GBLinearModel(LearnerModelParam const* learner_model_param) :
       learner_model_param {learner_model_param} {}
-  void Configure(Args const &cfg) { }
+  void Configure(Args const &) { }
 
   // weight for each of feature, bias is the last one
   std::vector<bst_float> weight;
diff --git a/src/learner.cc b/src/learner.cc
index 85ca3a503..34fe19cd1 100644
--- a/src/learner.cc
+++ b/src/learner.cc
@@ -341,7 +341,7 @@ class LearnerConfiguration : public Learner {
 
   void LoadConfig(Json const& in) override {
     CHECK(IsA<Object>(in));
-    Version::Load(in, true);
+    Version::Load(in);
 
     auto const& learner_parameters = get<Object>(in["learner"]);
     FromJson(learner_parameters.at("learner_train_param"), &tparam_);
@@ -623,7 +623,7 @@ class LearnerIO : public LearnerConfiguration {
 
   void LoadModel(Json const& in) override {
     CHECK(IsA<Object>(in));
-    Version::Load(in, false);
+    Version::Load(in);
     auto const& learner = get<Object>(in["learner"]);
     mparam_.FromJson(learner.at("learner_model_param"));
 
diff --git a/src/metric/metric.cc b/src/metric/metric.cc
index 2e1392e30..e2ee04cf4 100644
--- a/src/metric/metric.cc
+++ b/src/metric/metric.cc
@@ -11,7 +11,7 @@
 
 namespace xgboost {
 template <typename MetricRegistry>
-Metric* CreateMetricImpl(const std::string& name, GenericParameter const* tparam) {
+Metric* CreateMetricImpl(const std::string& name) {
   std::string buf = name;
   std::string prefix = name;
   const char* param;
@@ -44,7 +44,7 @@ Metric* CreateMetricImpl(const std::string& name, GenericParameter const* tparam
 
 Metric *
 Metric::Create(const std::string& name, GenericParameter const* tparam) {
-  auto metric = CreateMetricImpl<MetricReg>(name, tparam);
+  auto metric = CreateMetricImpl<MetricReg>(name);
   if (metric == nullptr) {
     LOG(FATAL) << "Unknown metric function " << name;
   }
@@ -55,7 +55,7 @@ Metric::Create(const std::string& name, GenericParameter const* tparam) {
 
 Metric *
 GPUMetric::CreateGPUMetric(const std::string& name, GenericParameter const* tparam) {
-  auto metric = CreateMetricImpl<MetricGPUReg>(name, tparam);
+  auto metric = CreateMetricImpl<MetricGPUReg>(name);
   if (metric == nullptr) {
     LOG(WARNING) << "Cannot find a GPU metric builder for metric " << name
                  << ". Resorting to the CPU builder";
diff --git a/src/metric/rank_metric.cc b/src/metric/rank_metric.cc
index b55c764d2..cfbae468c 100644
--- a/src/metric/rank_metric.cc
+++ b/src/metric/rank_metric.cc
@@ -55,13 +55,13 @@ class PerInstanceWeightPolicy {
  public:
   inline static xgboost::bst_float
   GetWeightOfInstance(const xgboost::MetaInfo& info,
-                      unsigned instance_id, unsigned group_id) {
+                      unsigned instance_id, unsigned) {
     return info.GetWeight(instance_id);
   }
   inline static xgboost::bst_float
   GetWeightOfSortedRecord(const xgboost::MetaInfo& info,
                           const PredIndPairContainer& rec,
-                          unsigned record_id, unsigned group_id) {
+                          unsigned record_id, unsigned) {
     return info.GetWeight(rec[record_id].second);
   }
 };
@@ -70,14 +70,14 @@ class PerGroupWeightPolicy {
  public:
   inline static xgboost::bst_float
   GetWeightOfInstance(const xgboost::MetaInfo& info,
-                      unsigned instance_id, unsigned group_id) {
+                      unsigned, unsigned group_id) {
     return info.GetWeight(group_id);
   }
 
   inline static xgboost::bst_float
   GetWeightOfSortedRecord(const xgboost::MetaInfo& info,
-                          const PredIndPairContainer& rec,
-                          unsigned record_id, unsigned group_id) {
+                          const PredIndPairContainer&,
+                          unsigned, unsigned group_id) {
     return info.GetWeight(group_id);
   }
 };
@@ -651,11 +651,11 @@ XGBOOST_REGISTER_METRIC(AMS, "ams")
 
 XGBOOST_REGISTER_METRIC(Auc, "auc")
 .describe("Area under curve for both classification and rank.")
-.set_body([](const char* param) { return new EvalAuc(); });
+.set_body([](const char*) { return new EvalAuc(); });
 
 XGBOOST_REGISTER_METRIC(AucPR, "aucpr")
 .describe("Area under PR curve for both classification and rank.")
-.set_body([](const char* param) { return new EvalAucPR(); });
+.set_body([](const char*) { return new EvalAucPR(); });
 
 XGBOOST_REGISTER_METRIC(Precision, "pre")
 .describe("precision@k for rank.")
@@ -671,6 +671,6 @@ XGBOOST_REGISTER_METRIC(MAP, "map")
 
 XGBOOST_REGISTER_METRIC(Cox, "cox-nloglik")
 .describe("Negative log partial likelihood of Cox proportioanl hazards model.")
-.set_body([](const char* param) { return new EvalCox(); });
+.set_body([](const char*) { return new EvalCox(); });
 }  // namespace metric
 }  // namespace xgboost
diff --git a/src/predictor/predictor.cc b/src/predictor/predictor.cc
index 2a310ba10..9aa18b19c 100644
--- a/src/predictor/predictor.cc
+++ b/src/predictor/predictor.cc
@@ -47,7 +47,7 @@ decltype(PredictionContainer::container_) const& PredictionContainer::Container(
 }
 
 void Predictor::Configure(
-    const std::vector<std::pair<std::string, std::string>>& cfg) {
+    const std::vector<std::pair<std::string, std::string>>&) {
 }
 Predictor* Predictor::Create(
     std::string const& name, GenericParameter const* generic_param) {
diff --git a/src/tree/split_evaluator.h b/src/tree/split_evaluator.h
index 40550024f..fc7fe65fb 100644
--- a/src/tree/split_evaluator.h
+++ b/src/tree/split_evaluator.h
@@ -107,7 +107,7 @@ class TreeEvaluator {
         return w;
       }
     }
-    XGBOOST_DEVICE float CalcGainGivenWeight(bst_node_t nid, ParamT const &p,
+    XGBOOST_DEVICE float CalcGainGivenWeight(bst_node_t, ParamT const &p,
                                              tree::GradStats stats, float w) const {
       if (stats.GetHess() <= 0) {
         return .0f;
@@ -149,7 +149,7 @@ class TreeEvaluator {
       return;
     }
     common::Transform<>::Init(
-        [=] XGBOOST_DEVICE(size_t idx, common::Span<float> lower,
+        [=] XGBOOST_DEVICE(size_t, common::Span<float> lower,
                            common::Span<float> upper,
                            common::Span<int> monotone) {
           lower[leftid] = lower[nodeid];
diff --git a/src/tree/tree_model.cc b/src/tree/tree_model.cc
index e4253dbc4..35c052136 100644
--- a/src/tree/tree_model.cc
+++ b/src/tree/tree_model.cc
@@ -69,20 +69,24 @@ class TreeGenerator {
     return result;
   }
 
-  virtual std::string Indicator(RegTree const& tree, int32_t nid, uint32_t depth) const {
+  virtual std::string Indicator(RegTree const& /*tree*/,
+                                int32_t /*nid*/, uint32_t /*depth*/) const {
     return "";
   }
-  virtual std::string Integer(RegTree const& tree, int32_t nid, uint32_t depth) const {
+  virtual std::string Integer(RegTree const& /*tree*/,
+                                int32_t /*nid*/, uint32_t /*depth*/) const {
     return "";
   }
-  virtual std::string Quantitive(RegTree const& tree, int32_t nid, uint32_t depth) const {
+  virtual std::string Quantitive(RegTree const& /*tree*/,
+                                int32_t /*nid*/, uint32_t /*depth*/) const {
     return "";
   }
-  virtual std::string NodeStat(RegTree const& tree, int32_t nid) const {
+  virtual std::string NodeStat(RegTree const& /*tree*/, int32_t /*nid*/) const {
     return "";
   }
 
-  virtual std::string PlainNode(RegTree const& tree, int32_t nid, uint32_t depth) const = 0;
+  virtual std::string PlainNode(RegTree const& /*tree*/,
+                                int32_t /*nid*/, uint32_t /*depth*/) const = 0;
 
   virtual std::string SplitNode(RegTree const& tree, int32_t nid, uint32_t depth) {
     auto const split_index = tree[nid].SplitIndex();
@@ -179,7 +183,7 @@ class TextGenerator : public TreeGenerator {
   using SuperT = TreeGenerator;
 
  public:
-  TextGenerator(FeatureMap const& fmap, std::string const& attrs, bool with_stats) :
+  TextGenerator(FeatureMap const& fmap, bool with_stats) :
       TreeGenerator(fmap, with_stats) {}
 
   std::string LeafNode(RegTree const& tree, int32_t nid, uint32_t depth) const override {
@@ -196,7 +200,7 @@ class TextGenerator : public TreeGenerator {
     return result;
   }
 
-  std::string Indicator(RegTree const& tree, int32_t nid, uint32_t depth) const override {
+  std::string Indicator(RegTree const& tree, int32_t nid, uint32_t) const override {
     static std::string const kIndicatorTemplate = "{nid}:[{fname}] yes={yes},no={no}";
     int32_t nyes = tree[nid].DefaultLeft() ?
                    tree[nid].RightChild() : tree[nid].LeftChild();
@@ -288,14 +292,14 @@ class TextGenerator : public TreeGenerator {
 XGBOOST_REGISTER_TREE_IO(TextGenerator, "text")
 .describe("Dump text representation of tree")
 .set_body([](FeatureMap const& fmap, std::string const& attrs, bool with_stats) {
-            return new TextGenerator(fmap, attrs, with_stats);
+            return new TextGenerator(fmap, with_stats);
           });
 
 class JsonGenerator : public TreeGenerator {
   using SuperT = TreeGenerator;
 
  public:
-  JsonGenerator(FeatureMap const& fmap, std::string attrs, bool with_stats) :
+  JsonGenerator(FeatureMap const& fmap, bool with_stats) :
       TreeGenerator(fmap, with_stats) {}
 
   std::string Indent(uint32_t depth) const {
@@ -306,7 +310,7 @@ class JsonGenerator : public TreeGenerator {
     return result;
   }
 
-  std::string LeafNode(RegTree const& tree, int32_t nid, uint32_t depth) const override {
+  std::string LeafNode(RegTree const& tree, int32_t nid, uint32_t) const override {
     static std::string const kLeafTemplate =
         R"L({ "nodeid": {nid}, "leaf": {leaf} {stat}})L";
     static std::string const kStatTemplate =
@@ -426,7 +430,7 @@ class JsonGenerator : public TreeGenerator {
 XGBOOST_REGISTER_TREE_IO(JsonGenerator, "json")
 .describe("Dump json representation of tree")
 .set_body([](FeatureMap const& fmap, std::string const& attrs, bool with_stats) {
-            return new JsonGenerator(fmap, attrs, with_stats);
+            return new JsonGenerator(fmap, with_stats);
           });
 
 struct GraphvizParam : public XGBoostParameter<GraphvizParam> {
@@ -531,7 +535,7 @@ class GraphvizGenerator : public TreeGenerator {
  protected:
   // Only indicator is different, so we combine all different node types into this
   // function.
-  std::string PlainNode(RegTree const& tree, int32_t nid, uint32_t depth) const override {
+  std::string PlainNode(RegTree const& tree, int32_t nid, uint32_t) const override {
     auto split = tree[nid].SplitIndex();
     auto cond = tree[nid].SplitCond();
     static std::string const kNodeTemplate =
@@ -565,7 +569,7 @@ class GraphvizGenerator : public TreeGenerator {
     return result;
   };
 
-  std::string LeafNode(RegTree const& tree, int32_t nid, uint32_t depth) const override {
+  std::string LeafNode(RegTree const& tree, int32_t nid, uint32_t) const override {
     static std::string const kLeafTemplate =
         "    {nid} [ label=\"leaf={leaf-value}\" {params}]\n";
     auto result = SuperT::Match(kLeafTemplate, {
diff --git a/src/tree/updater_colmaker.cc b/src/tree/updater_colmaker.cc
index 2cd86a7aa..70a1f4dab 100644
--- a/src/tree/updater_colmaker.cc
+++ b/src/tree/updater_colmaker.cc
@@ -163,7 +163,7 @@ class ColMaker: public TreeUpdater {
                         DMatrix* p_fmat,
                         RegTree* p_tree) {
       std::vector<int> newnodes;
-      this->InitData(gpair, *p_fmat, *p_tree);
+      this->InitData(gpair, *p_fmat);
       this->InitNewNode(qexpand_, gpair, *p_fmat, *p_tree);
       for (int depth = 0; depth < param_.max_depth; ++depth) {
         this->FindSplit(depth, qexpand_, gpair, p_fmat, p_tree);
@@ -200,8 +200,7 @@ class ColMaker: public TreeUpdater {
    protected:
     // initialize temp data structure
     inline void InitData(const std::vector<GradientPair>& gpair,
-                         const DMatrix& fmat,
-                         const RegTree& tree) {
+                         const DMatrix& fmat) {
       {
         // setup position
         position_.resize(gpair.size());
@@ -439,7 +438,7 @@ class ColMaker: public TreeUpdater {
     virtual void UpdateSolution(const SparsePage &batch,
                                 const std::vector<bst_feature_t> &feat_set,
                                 const std::vector<GradientPair> &gpair,
-                                DMatrix*p_fmat) {
+                                DMatrix*) {
       // start enumeration
       const auto num_features = static_cast<bst_omp_uint>(feat_set.size());
 #if defined(_OPENMP)
diff --git a/src/tree/updater_histmaker.cc b/src/tree/updater_histmaker.cc
index 6deb42113..7edceee72 100644
--- a/src/tree/updater_histmaker.cc
+++ b/src/tree/updater_histmaker.cc
@@ -56,13 +56,6 @@ class HistMaker: public BaseMaker {
     HistUnit(const float *cut, GradStats *data, uint32_t size)
         : cut{cut}, data{data}, size{size} {}
     /*! \brief add a histogram to data */
-    void Add(float fv, const std::vector<GradientPair> &gpair,
-             const MetaInfo &info, const size_t ridx) {
-      unsigned bin = std::upper_bound(cut, cut + size, fv) - cut;
-      CHECK_NE(size, 0U) << "try insert into size=0";
-      CHECK_LT(bin, size);
-      data[bin].Add(gpair[ridx]);
-    }
   };
   /*! \brief a set of histograms from different index */
   struct HistSet {
@@ -86,7 +79,7 @@ class HistMaker: public BaseMaker {
     // per thread histset
     std::vector<HistSet> hset;
     // initialize the hist set
-    inline void Configure(const TrainParam &param, int nthread) {
+    inline void Configure(int nthread) {
       hset.resize(nthread);
       // cleanup statistics
       for (int tid = 0; tid < nthread; ++tid) {
@@ -127,7 +120,7 @@ class HistMaker: public BaseMaker {
       // create histogram
       this->CreateHist(gpair, p_fmat, selected_features_, *p_tree);
       // find split based on histogram statistics
-      this->FindSplit(depth, gpair, p_fmat, selected_features_, p_tree);
+      this->FindSplit(selected_features_, p_tree);
       // reset position after split
       this->ResetPositionAfterSplit(p_fmat, *p_tree);
       this->UpdateQueueExpand(*p_tree);
@@ -159,9 +152,9 @@ class HistMaker: public BaseMaker {
                                        const RegTree &tree) {
   }
   virtual void CreateHist(const std::vector<GradientPair> &gpair,
-                          DMatrix *p_fmat,
+                          DMatrix *,
                           const std::vector <bst_feature_t> &fset,
-                          const RegTree &tree)  = 0;
+                          const RegTree &)  = 0;
 
  private:
   void EnumerateSplit(const HistUnit &hist,
@@ -202,10 +195,7 @@ class HistMaker: public BaseMaker {
     }
   }
 
-  void FindSplit(int depth,
-                 const std::vector<GradientPair> &gpair,
-                 DMatrix *p_fmat,
-                 const std::vector <bst_feature_t> &feature_set,
+  void FindSplit(const std::vector <bst_feature_t> &feature_set,
                  RegTree *p_tree) {
     const size_t num_feature = feature_set.size();
     // get the best split condition for each node
@@ -288,7 +278,6 @@ class CQHistMaker: public HistMaker {
      */
     inline void Add(bst_float fv,
                     const std::vector<GradientPair> &gpair,
-                    const MetaInfo &info,
                     const bst_uint ridx) {
       while (istart < hist.size && !(fv < hist.cut[istart])) ++istart;
       CHECK_NE(istart, hist.size);
@@ -342,7 +331,7 @@ class CQHistMaker: public HistMaker {
       feat2workindex_[fset[i]] = static_cast<int>(i);
     }
     // start to work
-    this->wspace_.Configure(this->param_, 1);
+    this->wspace_.Configure(1);
     // if it is C++11, use lazy evaluation for Allreduce,
     // to gain speedup in recovery
     auto lazy_get_hist = [&]() {
@@ -376,7 +365,7 @@ class CQHistMaker: public HistMaker {
                              this->wspace_.hset[0].data.size(), lazy_get_hist);
   }
 
-  void ResetPositionAfterSplit(DMatrix *p_fmat,
+  void ResetPositionAfterSplit(DMatrix *,
                                  const RegTree &tree) override {
     this->GetSplitSet(this->qexpand_, tree, &fsplit_set_);
   }
@@ -533,7 +522,7 @@ class CQHistMaker: public HistMaker {
         const bst_uint ridx = c.index;
         const int nid = this->position_[ridx];
         if (nid >= 0) {
-          hbuilder[nid].Add(c.fvalue, gpair, info, ridx);
+          hbuilder[nid].Add(c.fvalue, gpair, ridx);
         }
       }
     }
@@ -689,7 +678,7 @@ class GlobalProposalHistMaker: public CQHistMaker {
       this->feat2workindex_[fset[i]] = static_cast<int>(i);
     }
     // start to work
-    this->wspace_.Configure(this->param_, 1);
+    this->wspace_.Configure(1);
     // to gain speedup in recovery
     {
       this->thread_hist_.resize(omp_get_max_threads());