--- a/hotspot/src/share/vm/runtime/sweeper.hpp Fri Sep 27 08:39:19 2013 +0200
+++ b/hotspot/src/share/vm/runtime/sweeper.hpp Fri Sep 27 10:50:55 2013 +0200
@@ -27,8 +27,30 @@
// An NmethodSweeper is an incremental cleaner for:
// - cleanup inline caches
-// - reclamation of unreferences zombie nmethods
-//
+// - reclamation of nmethods
+// Removing nmethods from the code cache includes two operations
+// 1) mark active nmethods
+// Is done in 'mark_active_nmethods()'. This function is called at a
+// safepoint and marks all nmethods that are active on a thread's stack.
+// 2) sweep nmethods
+// Is done in sweep_code_cache(). This function is the only place in the
+// sweeper where memory is reclaimed. Note that sweep_code_cache() is not
+// called at a safepoint. However, sweep_code_cache() stops executing if
+// another thread requests a safepoint. Consequently, 'mark_active_nmethods()'
+// and sweep_code_cache() cannot execute at the same time.
+// To reclaim memory, nmethods are first marked as 'not-entrant'. Methods can
+// be made not-entrant by (i) the sweeper, (ii) deoptimization, (iii) dependency
+// invalidation, and (iv) being replaced be a different method version (tiered
+// compilation). Not-entrant nmethod cannot be called by Java threads, but they
+// can still be active on the stack. To ensure that active nmethod are not reclaimed,
+// we have to wait until the next marking phase has completed. If a not-entrant
+// nmethod was NOT marked as active, it can be converted to 'zombie' state. To safely
+// remove the nmethod, all inline caches (IC) that point to the the nmethod must be
+// cleared. After that, the nmethod can be evicted from the code cache. Each nmethod's
+// state change happens during separate sweeps. It may take at least 3 sweeps before an
+// nmethod's space is freed. Sweeping is currently done by compiler threads between
+// compilations or at least each 5 sec (NmethodSweepCheckInterval) when the code cache
+// is full.
class NMethodSweeper : public AllStatic {
static long _traversals; // Stack scan count, also sweep ID.
@@ -41,46 +63,38 @@
static volatile int _invocations; // No. of invocations left until we are completed with this pass
static volatile int _sweep_started; // Flag to control conc sweeper
- //The following are reset in scan_stacks and synchronized by the safepoint
- static bool _resweep; // Indicates that a change has happend and we want another sweep,
- // always checked and reset at a safepoint so memory will be in sync.
- static int _locked_seen; // Number of locked nmethods encountered during the scan
+ //The following are reset in mark_active_nmethods and synchronized by the safepoint
+ static bool _request_mark_phase; // Indicates that a change has happend and we need another mark pahse,
+ // always checked and reset at a safepoint so memory will be in sync.
+ static int _locked_seen; // Number of locked nmethods encountered during the scan
static int _not_entrant_seen_on_stack; // Number of not entrant nmethod were are still on stack
- static jint _flush_token; // token that guards method flushing, making sure it is executed only once.
-
- // These are set during a flush, a VM-operation
- static long _last_flush_traversal_id; // trav number at last flush unloading
- static jlong _last_full_flush_time; // timestamp of last emergency unloading
-
- // These are synchronized by the _sweep_started token
- static int _highest_marked; // highest compile id dumped at last emergency unloading
- static int _dead_compile_ids; // number of compile ids that where not in the cache last flush
// Stat counters
- static int _number_of_flushes; // Total of full traversals caused by full cache
static int _total_nof_methods_reclaimed; // Accumulated nof methods flushed
static jlong _total_time_sweeping; // Accumulated time sweeping
static jlong _total_time_this_sweep; // Total time this sweep
static jlong _peak_sweep_time; // Peak time for a full sweep
static jlong _peak_sweep_fraction_time; // Peak time sweeping one fraction
- static jlong _total_disconnect_time; // Total time cleaning code mem
- static jlong _peak_disconnect_time; // Peak time cleaning code mem
- static void process_nmethod(nmethod *nm);
+ static int process_nmethod(nmethod *nm);
static void release_nmethod(nmethod* nm);
- static void log_sweep(const char* msg, const char* format = NULL, ...);
static bool sweep_in_progress();
+ static void sweep_code_cache();
+ static void request_nmethod_marking() { _request_mark_phase = true; }
+ static void reset_nmethod_marking() { _request_mark_phase = false; }
+ static bool need_marking_phase() { return _request_mark_phase; }
+
+ static int _hotness_counter_reset_val;
public:
static long traversal_count() { return _traversals; }
- static int number_of_flushes() { return _number_of_flushes; }
static int total_nof_methods_reclaimed() { return _total_nof_methods_reclaimed; }
static jlong total_time_sweeping() { return _total_time_sweeping; }
static jlong peak_sweep_time() { return _peak_sweep_time; }
static jlong peak_sweep_fraction_time() { return _peak_sweep_fraction_time; }
- static jlong total_disconnect_time() { return _total_disconnect_time; }
- static jlong peak_disconnect_time() { return _peak_disconnect_time; }
+ static void log_sweep(const char* msg, const char* format = NULL, ...);
+
#ifdef ASSERT
static bool is_sweeping(nmethod* which) { return _current == which; }
@@ -90,19 +104,18 @@
static void report_events();
#endif
- static void scan_stacks(); // Invoked at the end of each safepoint
- static void sweep_code_cache(); // Concurrent part of sweep job
- static void possibly_sweep(); // Compiler threads call this to sweep
+ static void mark_active_nmethods(); // Invoked at the end of each safepoint
+ static void possibly_sweep(); // Compiler threads call this to sweep
- static void notify(nmethod* nm) {
+ static int sort_nmethods_by_hotness(nmethod** nm1, nmethod** nm2);
+ static int hotness_counter_reset_val();
+
+ static void notify() {
// Request a new sweep of the code cache from the beginning. No
// need to synchronize the setting of this flag since it only
// changes to false at safepoint so we can never overwrite it with false.
- _resweep = true;
+ request_nmethod_marking();
}
-
- static void handle_full_code_cache(bool is_full); // Called by compilers who fail to allocate
- static void speculative_disconnect_nmethods(bool was_full); // Called by vm op to deal with alloc failure
};
#endif // SHARE_VM_RUNTIME_SWEEPER_HPP