1 /*
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   3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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   5  * This code is free software; you can redistribute it and/or modify it
   6  * under the terms of the GNU General Public License version 2 only, as
   7  * published by the Free Software Foundation.
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   9  * This code is distributed in the hope that it will be useful, but WITHOUT
  10  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  11  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  12  * version 2 for more details (a copy is included in the LICENSE file that
  13  * accompanied this code).
  14  *
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  17  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
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  19  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
  20  * or visit www.oracle.com if you need additional information or have any
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  24 
  25 #ifndef SHARE_VM_RUNTIME_SWEEPER_HPP
  26 #define SHARE_VM_RUNTIME_SWEEPER_HPP
  27 
  28 #include "utilities/ticks.hpp"
  29 // An NmethodSweeper is an incremental cleaner for:
  30 //    - cleanup inline caches
  31 //    - reclamation of nmethods
  32 // Removing nmethods from the code cache includes two operations
  33 //  1) mark active nmethods
  34 //     Is done in 'mark_active_nmethods()'. This function is called at a
  35 //     safepoint and marks all nmethods that are active on a thread's stack.
  36 //  2) sweep nmethods
  37 //     Is done in sweep_code_cache(). This function is the only place in the
  38 //     sweeper where memory is reclaimed. Note that sweep_code_cache() is not
  39 //     called at a safepoint. However, sweep_code_cache() stops executing if
  40 //     another thread requests a safepoint. Consequently, 'mark_active_nmethods()'
  41 //     and sweep_code_cache() cannot execute at the same time.
  42 //     To reclaim memory, nmethods are first marked as 'not-entrant'. Methods can
  43 //     be made not-entrant by (i) the sweeper, (ii) deoptimization, (iii) dependency
  44 //     invalidation, and (iv) being replaced be a different method version (tiered
  45 //     compilation). Not-entrant nmethod cannot be called by Java threads, but they
  46 //     can still be active on the stack. To ensure that active nmethod are not reclaimed,
  47 //     we have to wait until the next marking phase has completed. If a not-entrant
  48 //     nmethod was NOT marked as active, it can be converted to 'zombie' state. To safely
  49 //     remove the nmethod, all inline caches (IC) that point to the the nmethod must be
  50 //     cleared. After that, the nmethod can be evicted from the code cache. Each nmethod's
  51 //     state change happens during separate sweeps. It may take at least 3 sweeps before an
  52 //     nmethod's space is freed. Sweeping is currently done by compiler threads between
  53 //     compilations or at least each 5 sec (NmethodSweepCheckInterval) when the code cache
  54 //     is full.
  55 
  56 class NMethodSweeper : public AllStatic {
  57   static long      _traversals;                   // Stack scan count, also sweep ID.
  58   static long      _total_nof_code_cache_sweeps;  // Total number of full sweeps of the code cache
  59   static long      _time_counter;                 // Virtual time used to periodically invoke sweeper
  60   static long      _last_sweep;                   // Value of _time_counter when the last sweep happened
  61   static NMethodIterator _current;                // Current nmethod
  62   static int       _seen;                         // Nof. nmethod we have currently processed in current pass of CodeCache
  63   static int       _flushed_count;                // Nof. nmethods flushed in current sweep
  64   static int       _zombified_count;              // Nof. nmethods made zombie in current sweep
  65   static int       _marked_for_reclamation_count; // Nof. nmethods marked for reclaim in current sweep
  66 
  67   static volatile int  _sweep_fractions_left;     // Nof. invocations left until we are completed with this pass
  68   static volatile int  _sweep_started;            // Flag to control conc sweeper
  69   static volatile bool _should_sweep;             // Indicates if we should invoke the sweeper
  70   static volatile int _bytes_changed;             // Counts the total nmethod size if the nmethod changed from:
  71                                                   //   1) alive       -> not_entrant
  72                                                   //   2) not_entrant -> zombie
  73                                                   //   3) zombie      -> marked_for_reclamation
  74   // Stat counters
  75   static long      _total_nof_methods_reclaimed;    // Accumulated nof methods flushed
  76   static long      _total_nof_c2_methods_reclaimed; // Accumulated nof C2-compiled methods flushed
  77   static size_t    _total_flushed_size;             // Total size of flushed methods
  78   static int       _hotness_counter_reset_val;
  79 
  80   static Tickspan  _total_time_sweeping;          // Accumulated time sweeping
  81   static Tickspan  _total_time_this_sweep;        // Total time this sweep
  82   static Tickspan  _peak_sweep_time;              // Peak time for a full sweep
  83   static Tickspan  _peak_sweep_fraction_time;     // Peak time sweeping one fraction
  84 
  85   static int  process_nmethod(nmethod *nm);
  86   static void release_nmethod(nmethod* nm);
  87 
  88   static bool sweep_in_progress();
  89   static void sweep_code_cache();
  90 
  91  public:
  92   static long traversal_count()              { return _traversals; }
  93   static int  total_nof_methods_reclaimed()  { return _total_nof_methods_reclaimed; }
  94   static const Tickspan total_time_sweeping()      { return _total_time_sweeping; }
  95   static const Tickspan peak_sweep_time()          { return _peak_sweep_time; }
  96   static const Tickspan peak_sweep_fraction_time() { return _peak_sweep_fraction_time; }
  97   static void log_sweep(const char* msg, const char* format = NULL, ...) ATTRIBUTE_PRINTF(2, 3);
  98 
  99 
 100 #ifdef ASSERT
 101   static bool is_sweeping(nmethod* which) { return _current.method() == which; }
 102   // Keep track of sweeper activity in the ring buffer
 103   static void record_sweep(nmethod* nm, int line);
 104   static void report_events(int id, address entry);
 105   static void report_events();
 106 #endif
 107 
 108   static void mark_active_nmethods();      // Invoked at the end of each safepoint
 109   static void possibly_sweep();            // Compiler threads call this to sweep
 110 
 111   static int hotness_counter_reset_val();
 112   static void report_state_change(nmethod* nm);
 113   static void possibly_enable_sweeper();
 114   static void possibly_flush(nmethod* nm);
 115   static void print();   // Printing/debugging
 116 };
 117 
 118 #endif // SHARE_VM_RUNTIME_SWEEPER_HPP