--- old/src/share/vm/runtime/sweeper.hpp 2013-09-13 17:13:59.825025281 +0200 +++ new/src/share/vm/runtime/sweeper.hpp 2013-09-13 17:13:59.777025282 +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 int sort_nmethods_by_hotness(nmethod** nm1, nmethod** nm2); + static int hotness_counter_reset_val(); - static void notify(nmethod* nm) { + 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