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diff --git a/src/mds/MDBalancer.h b/src/mds/MDBalancer.h
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+// -*- mode:C++; tab-width:8; c-basic-offset:2; indent-tabs-mode:t -*- 
+// vim: ts=8 sw=2 smarttab
+/*
+ * Ceph - scalable distributed file system
+ *
+ * Copyright (C) 2004-2006 Sage Weil <sage@newdream.net>
+ *
+ * This is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License version 2.1, as published by the Free Software 
+ * Foundation.  See file COPYING.
+ * 
+ */
+
+
+
+#ifndef CEPH_MDBALANCER_H
+#define CEPH_MDBALANCER_H
+
+#include <list>
+#include <map>
+
+#include "include/types.h"
+#include "common/Clock.h"
+#include "common/Cond.h"
+
+#include "msg/Message.h"
+#include "messages/MHeartbeat.h"
+
+#include "MDSMap.h"
+
+class MDSRank;
+class MHeartbeat;
+class CInode;
+class CDir;
+class Messenger;
+class MonClient;
+
+class MDBalancer {
+public:
+  using clock = ceph::coarse_mono_clock;
+  using time = ceph::coarse_mono_time;
+  friend class C_Bal_SendHeartbeat;
+
+  MDBalancer(MDSRank *m, Messenger *msgr, MonClient *monc);
+
+  void handle_conf_change(const std::set<std::string>& changed, const MDSMap& mds_map);
+
+  int proc_message(const Message::const_ref &m);
+
+  /**
+   * Regularly called upkeep function.
+   *
+   * Sends MHeartbeat messages to the mons.
+   */
+  void tick();
+
+  void subtract_export(CDir *ex);
+  void add_import(CDir *im);
+  void adjust_pop_for_rename(CDir *pdir, CDir *dir, bool inc);
+
+  void hit_inode(CInode *in, int type, int who=-1);
+  void hit_dir(CDir *dir, int type, int who=-1, double amount=1.0);
+
+  void queue_split(const CDir *dir, bool fast);
+  void queue_merge(CDir *dir);
+
+  /**
+   * Based on size and configuration, decide whether to issue a queue_split
+   * or queue_merge for this CDir.
+   *
+   * \param hot whether the directory's temperature is enough to split it
+   */
+  void maybe_fragment(CDir *dir, bool hot);
+
+  void handle_mds_failure(mds_rank_t who);
+
+  int dump_loads(Formatter *f);
+
+private:
+  bool bal_fragment_dirs;
+  int64_t bal_fragment_interval;
+  static const unsigned int AUTH_TREES_THRESHOLD = 5;
+
+  typedef struct {
+    std::map<mds_rank_t, double> targets;
+    std::map<mds_rank_t, double> imported;
+    std::map<mds_rank_t, double> exported;
+  } balance_state_t;
+
+  //set up the rebalancing targets for export and do one if the
+  //MDSMap is up to date
+  void prep_rebalance(int beat);
+  int mantle_prep_rebalance();
+
+  void handle_export_pins(void);
+
+  mds_load_t get_load();
+  int localize_balancer();
+  void send_heartbeat();
+  void handle_heartbeat(const MHeartbeat::const_ref &m);
+  void find_exports(CDir *dir,
+                    double amount,
+                    std::list<CDir*>& exports,
+                    double& have,
+                    set<CDir*>& already_exporting);
+
+  double try_match(balance_state_t &state,
+                   mds_rank_t ex, double& maxex,
+                   mds_rank_t im, double& maxim);
+
+  double get_maxim(balance_state_t &state, mds_rank_t im) {
+    return target_load - mds_meta_load[im] - state.imported[im];
+  }
+  double get_maxex(balance_state_t &state, mds_rank_t ex) {
+    return mds_meta_load[ex] - target_load - state.exported[ex];
+  }
+
+  /**
+   * Try to rebalance.
+   *
+   * Check if the monitor has recorded the current export targets;
+   * if it has then do the actual export. Otherwise send off our
+   * export targets message again.
+   */
+  void try_rebalance(balance_state_t& state);
+
+  MDSRank *mds;
+  Messenger *messenger;
+  MonClient *mon_client;
+  int beat_epoch = 0;
+
+  string bal_code;
+  string bal_version;
+
+  time last_heartbeat = clock::zero();
+  time last_sample = clock::zero();
+  time rebalance_time = clock::zero(); //ensure a consistent view of load for rebalance
+
+  time last_get_load = clock::zero();
+  uint64_t last_num_requests = 0;
+  uint64_t last_cpu_time = 0;
+
+  // Dirfrags which are marked to be passed on to MDCache::[split|merge]_dir
+  // just as soon as a delayed context comes back and triggers it.
+  // These sets just prevent us from spawning extra timer contexts for
+  // dirfrags that already have one in flight.
+  set<dirfrag_t>   split_pending, merge_pending;
+
+  // per-epoch scatter/gathered info
+  std::map<mds_rank_t, mds_load_t>  mds_load;
+  std::map<mds_rank_t, double>       mds_meta_load;
+  std::map<mds_rank_t, map<mds_rank_t, float> > mds_import_map;
+  std::map<mds_rank_t, int> mds_last_epoch_under_map;
+
+  // per-epoch state
+  double my_load = 0;
+  double target_load = 0;
+};
+
+#endif