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src/hotspot/share/gc/shenandoah/shenandoah_globals.hpp

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 45   product(size_t, ShenandoahMinRegionSize, 256 * K, EXPERIMENTAL,           \
 46           "With automatic region sizing, the regions would be at least "    \
 47           "this large.")                                                    \
 48                                                                             \
 49   product(size_t, ShenandoahMaxRegionSize, 32 * M, EXPERIMENTAL,            \
 50           "With automatic region sizing, the regions would be at most "     \
 51           "this large.")                                                    \
 52                                                                             \
 53   product(intx, ShenandoahHumongousThreshold, 100, EXPERIMENTAL,            \
 54           "Humongous objects are allocated in separate regions. "           \
 55           "This setting defines how large the object should be to be "      \
 56           "deemed humongous. Value is in  percents of heap region size. "   \
 57           "This also caps the maximum TLAB size.")                          \
 58           range(1, 100)                                                     \
 59                                                                             \
 60   product(ccstr, ShenandoahGCMode, "satb",                                  \
 61           "GC mode to use.  Among other things, this defines which "        \
 62           "barriers are in in use. Possible values are:"                    \
 63           " satb - snapshot-at-the-beginning concurrent GC (three pass mark-evac-update);"  \
 64           " iu - incremental-update concurrent GC (three pass mark-evac-update);"  \
 65           " passive - stop the world GC only (either degenerated or full)") \

 66                                                                             \
 67   product(ccstr, ShenandoahGCHeuristics, "adaptive",                        \
 68           "GC heuristics to use. This fine-tunes the GC mode selected, "    \
 69           "by choosing when to start the GC, how much to process on each "  \
 70           "cycle, and what other features to automatically enable. "        \
 71           "Possible values are:"                                            \
 72           " adaptive - adapt to maintain the given amount of free heap "    \
 73           "at all times, even during the GC cycle;"                         \
 74           " static -  trigger GC when free heap falls below the threshold;" \
 75           " aggressive - run GC continuously, try to evacuate everything;"  \
 76           " compact - run GC more frequently and with deeper targets to "   \
 77           "free up more memory.")                                           \
 78                                                                             \






 79   product(uintx, ShenandoahUnloadClassesFrequency, 1, EXPERIMENTAL,         \
 80           "Unload the classes every Nth cycle. Normally affects concurrent "\
 81           "GC cycles, as degenerated and full GCs would try to unload "     \
 82           "classes regardless. Set to zero to disable class unloading.")    \
 83                                                                             \
 84   product(uintx, ShenandoahGarbageThreshold, 25, EXPERIMENTAL,              \
 85           "How much garbage a region has to contain before it would be "    \
 86           "taken for collection. This a guideline only, as GC heuristics "  \
 87           "may select the region for collection even if it has little "     \
 88           "garbage. This also affects how much internal fragmentation the " \
 89           "collector accepts. In percents of heap region size.")            \
 90           range(0,100)                                                      \
 91                                                                             \





 92   product(uintx, ShenandoahInitFreeThreshold, 70, EXPERIMENTAL,             \
 93           "How much heap should be free before some heuristics trigger the "\
 94           "initial (learning) cycles. Affects cycle frequency on startup "  \
 95           "and after drastic state changes, e.g. after degenerated/full "   \
 96           "GC cycles. In percents of (soft) max heap size.")                \
 97           range(0,100)                                                      \
 98                                                                             \
 99   product(uintx, ShenandoahMinFreeThreshold, 10, EXPERIMENTAL,              \
100           "How much heap should be free before most heuristics trigger the "\
101           "collection, even without other triggers. Provides the safety "   \
102           "margin for many heuristics. In percents of (soft) max heap size.")\

103           range(0,100)                                                      \
104                                                                             \
105   product(uintx, ShenandoahAllocationThreshold, 0, EXPERIMENTAL,            \
106           "How many new allocations should happen since the last GC cycle " \
107           "before some heuristics trigger the collection. In percents of "  \
108           "(soft) max heap size. Set to zero to effectively disable.")      \
109           range(0,100)                                                      \
110                                                                             \
111   product(uintx, ShenandoahAllocSpikeFactor, 5, EXPERIMENTAL,               \
112           "How much of heap should some heuristics reserve for absorbing "  \
113           "the allocation spikes. Larger value wastes more memory in "      \
114           "non-emergency cases, but provides more safety in emergency "     \
115           "cases. In percents of (soft) max heap size.")                    \
116           range(0,100)                                                      \
117                                                                             \
118   product(uintx, ShenandoahLearningSteps, 5, EXPERIMENTAL,                  \
119           "The number of cycles some heuristics take to collect in order "  \
120           "to learn application and GC performance.")                       \
121           range(0,100)                                                      \
122                                                                             \

145   product(double, ShenandoahAdaptiveInitialSpikeThreshold, 1.8, EXPERIMENTAL, \
146           "If the most recently sampled allocation rate is more than "      \
147           "this many standard deviations away from the moving average, "    \
148           "then a cycle is initiated. This value controls how sensitive "   \
149           "the heuristic is to allocation spikes. Decreasing this number "  \
150           "increases the sensitivity. ")                                    \
151                                                                             \
152   product(double, ShenandoahAdaptiveDecayFactor, 0.5, EXPERIMENTAL,         \
153           "The decay factor (alpha) used for values in the weighted "       \
154           "moving average of cycle time and allocation rate. "              \
155           "Larger values give more weight to recent values.")               \
156           range(0,1.0)                                                      \
157                                                                             \
158   product(uintx, ShenandoahGuaranteedGCInterval, 5*60*1000, EXPERIMENTAL,   \
159           "Many heuristics would guarantee a concurrent GC cycle at "       \
160           "least with this interval. This is useful when large idle "       \
161           "intervals are present, where GC can run without stealing "       \
162           "time from active application. Time is in milliseconds. "         \
163           "Setting this to 0 disables the feature.")                        \
164                                                                             \





165   product(bool, ShenandoahAlwaysClearSoftRefs, false, EXPERIMENTAL,         \
166           "Unconditionally clear soft references, instead of using any "    \
167           "other cleanup policy. This minimizes footprint at expense of"    \
168           "more soft reference churn in applications.")                     \
169                                                                             \
170   product(bool, ShenandoahUncommit, true, EXPERIMENTAL,                     \
171           "Allow to uncommit memory under unused regions and metadata. "    \
172           "This optimizes footprint at expense of allocation latency in "   \
173           "regions that require committing back. Uncommits would be "       \
174           "disabled by some heuristics, or with static heap size.")         \
175                                                                             \
176   product(uintx, ShenandoahUncommitDelay, 5*60*1000, EXPERIMENTAL,          \
177           "Uncommit memory for regions that were not used for more than "   \
178           "this time. First use after that would incur allocation stalls. " \
179           "Actively used regions would never be uncommitted, because they " \
180           "do not become unused longer than this delay. Time is in "        \
181           "milliseconds. Setting this delay to 0 effectively uncommits "    \
182           "regions almost immediately after they become unused.")           \
183                                                                             \
184   product(bool, ShenandoahRegionSampling, false, EXPERIMENTAL,              \
185           "Provide heap region sampling data via jvmstat.")                 \
186                                                                             \
187   product(int, ShenandoahRegionSamplingRate, 40, EXPERIMENTAL,              \
188           "Sampling rate for heap region sampling. In milliseconds between "\
189           "the samples. Higher values provide more fidelity, at expense "   \
190           "of more sampling overhead.")                                     \
191                                                                             \









192   product(uintx, ShenandoahControlIntervalMin, 1, EXPERIMENTAL,             \
193           "The minimum sleep interval for the control loop that drives "    \
194           "the cycles. Lower values would increase GC responsiveness "      \
195           "to changing heap conditions, at the expense of higher perf "     \
196           "overhead. Time is in milliseconds.")                             \
197                                                                             \
198   product(uintx, ShenandoahControlIntervalMax, 10, EXPERIMENTAL,            \
199           "The maximum sleep interval for control loop that drives "        \
200           "the cycles. Lower values would increase GC responsiveness "      \
201           "to changing heap conditions, at the expense of higher perf "     \
202           "overhead. Time is in milliseconds.")                             \
203                                                                             \
204   product(uintx, ShenandoahControlIntervalAdjustPeriod, 1000, EXPERIMENTAL, \
205           "The time period for one step in control loop interval "          \
206           "adjustment. Lower values make adjustments faster, at the "       \
207           "expense of higher perf overhead. Time is in milliseconds.")      \
208                                                                             \
209   product(bool, ShenandoahVerify, false, DIAGNOSTIC,                        \
210           "Enable internal verification. This would catch many GC bugs, "   \
211           "but it would also stall the collector during the verification, " \
212           "which prolongs the pauses and might hide other bugs.")           \
213                                                                             \
214   product(intx, ShenandoahVerifyLevel, 4, DIAGNOSTIC,                       \
215           "Verification level, higher levels check more, taking more time. "\
216           "Accepted values are:"                                            \
217           " 0 = basic heap checks; "                                        \
218           " 1 = previous level, plus basic region checks; "                 \
219           " 2 = previous level, plus all roots; "                           \
220           " 3 = previous level, plus all reachable objects; "               \
221           " 4 = previous level, plus all marked objects")                   \
222                                                                             \
223   product(bool, ShenandoahElasticTLAB, true, DIAGNOSTIC,                    \
224           "Use Elastic TLABs with Shenandoah")                              \
225                                                                             \




226   product(uintx, ShenandoahEvacReserve, 5, EXPERIMENTAL,                    \
227           "How much of heap to reserve for evacuations. Larger values make "\
228           "GC evacuate more live objects on every cycle, while leaving "    \
229           "less headroom for application to allocate in. In percents of "   \
230           "total heap size.")                                               \
231           range(1,100)                                                      \
232                                                                             \
233   product(double, ShenandoahEvacWaste, 1.2, EXPERIMENTAL,                   \
234           "How much waste evacuations produce within the reserved space. "  \
235           "Larger values make evacuations more resilient against "          \
236           "evacuation conflicts, at expense of evacuating less on each "    \
237           "GC cycle.")                                                      \
238           range(1.0,100.0)                                                  \
239                                                                             \
240   product(bool, ShenandoahEvacReserveOverflow, true, EXPERIMENTAL,          \
241           "Allow evacuations to overflow the reserved space. Enabling it "  \
242           "will make evacuations more resilient when evacuation "           \
243           "reserve/waste is incorrect, at the risk that application "       \
244           "runs out of memory too early.")                                  \
245                                                                             \






246   product(bool, ShenandoahPacing, true, EXPERIMENTAL,                       \
247           "Pace application allocations to give GC chance to start "        \
248           "and complete before allocation failure is reached.")             \
249                                                                             \
250   product(uintx, ShenandoahPacingMaxDelay, 10, EXPERIMENTAL,                \
251           "Max delay for pacing application allocations. Larger values "    \
252           "provide more resilience against out of memory, at expense at "   \
253           "hiding the GC latencies in the allocation path. Time is in "     \
254           "milliseconds. Setting it to arbitrarily large value makes "      \
255           "GC effectively stall the threads indefinitely instead of going " \
256           "to degenerated or Full GC.")                                     \
257                                                                             \
258   product(uintx, ShenandoahPacingIdleSlack, 2, EXPERIMENTAL,                \
259           "How much of heap counted as non-taxable allocations during idle "\
260           "phases. Larger value makes the pacing milder when collector is " \
261           "idle, requiring less rendezvous with control thread. Lower "     \
262           "value makes the pacing control less responsive to out-of-cycle " \
263           "allocs. In percent of total heap size.")                         \
264           range(0, 100)                                                     \
265                                                                             \

349   product(bool, ShenandoahCloneBarrier, true, DIAGNOSTIC,                   \
350           "Turn on/off clone barriers in Shenandoah")                       \
351                                                                             \
352   product(bool, ShenandoahLoadRefBarrier, true, DIAGNOSTIC,                 \
353           "Turn on/off load-reference barriers in Shenandoah")              \
354                                                                             \
355   product(bool, ShenandoahNMethodBarrier, true, DIAGNOSTIC,                 \
356           "Turn on/off NMethod entry barriers in Shenandoah")               \
357                                                                             \
358   product(bool, ShenandoahStackWatermarkBarrier, true, DIAGNOSTIC,          \
359           "Turn on/off stack watermark barriers in Shenandoah")             \
360                                                                             \
361   develop(bool, ShenandoahVerifyOptoBarriers, false,                        \
362           "Verify no missing barriers in C2.")                              \
363                                                                             \
364   product(bool, ShenandoahLoopOptsAfterExpansion, true, DIAGNOSTIC,         \
365           "Attempt more loop opts after barrier expansion.")                \
366                                                                             \
367   product(bool, ShenandoahSelfFixing, true, DIAGNOSTIC,                     \
368           "Fix references with load reference barrier. Disabling this "     \
369           "might degrade performance.")






























370 
371 // end of GC_SHENANDOAH_FLAGS

372 
373 #endif // SHARE_GC_SHENANDOAH_SHENANDOAH_GLOBALS_HPP

 45   product(size_t, ShenandoahMinRegionSize, 256 * K, EXPERIMENTAL,           \
 46           "With automatic region sizing, the regions would be at least "    \
 47           "this large.")                                                    \
 48                                                                             \
 49   product(size_t, ShenandoahMaxRegionSize, 32 * M, EXPERIMENTAL,            \
 50           "With automatic region sizing, the regions would be at most "     \
 51           "this large.")                                                    \
 52                                                                             \
 53   product(intx, ShenandoahHumongousThreshold, 100, EXPERIMENTAL,            \
 54           "Humongous objects are allocated in separate regions. "           \
 55           "This setting defines how large the object should be to be "      \
 56           "deemed humongous. Value is in  percents of heap region size. "   \
 57           "This also caps the maximum TLAB size.")                          \
 58           range(1, 100)                                                     \
 59                                                                             \
 60   product(ccstr, ShenandoahGCMode, "satb",                                  \
 61           "GC mode to use.  Among other things, this defines which "        \
 62           "barriers are in in use. Possible values are:"                    \
 63           " satb - snapshot-at-the-beginning concurrent GC (three pass mark-evac-update);"  \
 64           " iu - incremental-update concurrent GC (three pass mark-evac-update);"  \
 65           " passive - stop the world GC only (either degenerated or full);" \
 66           " generational - generational concurrent GC")                     \
 67                                                                             \
 68   product(ccstr, ShenandoahGCHeuristics, "adaptive",                        \
 69           "GC heuristics to use. This fine-tunes the GC mode selected, "    \
 70           "by choosing when to start the GC, how much to process on each "  \
 71           "cycle, and what other features to automatically enable. "        \
 72           "Possible values are:"                                            \
 73           " adaptive - adapt to maintain the given amount of free heap "    \
 74           "at all times, even during the GC cycle;"                         \
 75           " static -  trigger GC when free heap falls below the threshold;" \
 76           " aggressive - run GC continuously, try to evacuate everything;"  \
 77           " compact - run GC more frequently and with deeper targets to "   \
 78           "free up more memory.")                                           \
 79                                                                             \
 80   product(ccstr, ShenandoahOldGCHeuristics, "adaptive",                     \
 81           "Similar to ShenandoahGCHeuristics, but applied to the old "      \
 82           "generation. This configuration is only used to trigger old "     \
 83           "collections and does not change how regions are selected "       \
 84           "for collection.")                                                \
 85                                                                             \
 86   product(uintx, ShenandoahUnloadClassesFrequency, 1, EXPERIMENTAL,         \
 87           "Unload the classes every Nth cycle. Normally affects concurrent "\
 88           "GC cycles, as degenerated and full GCs would try to unload "     \
 89           "classes regardless. Set to zero to disable class unloading.")    \
 90                                                                             \
 91   product(uintx, ShenandoahGarbageThreshold, 25, EXPERIMENTAL,              \
 92           "How much garbage a region has to contain before it would be "    \
 93           "taken for collection. This a guideline only, as GC heuristics "  \
 94           "may select the region for collection even if it has little "     \
 95           "garbage. This also affects how much internal fragmentation the " \
 96           "collector accepts. In percents of heap region size.")            \
 97           range(0,100)                                                      \
 98                                                                             \
 99   product(uintx, ShenandoahOldGarbageThreshold, 25, EXPERIMENTAL,           \
100           "How much garbage an old region has to contain before it would "  \
101           "be taken for collection.")                                       \
102           range(0,100)                                                      \
103                                                                             \
104   product(uintx, ShenandoahInitFreeThreshold, 70, EXPERIMENTAL,             \
105           "How much heap should be free before some heuristics trigger the "\
106           "initial (learning) cycles. Affects cycle frequency on startup "  \
107           "and after drastic state changes, e.g. after degenerated/full "   \
108           "GC cycles. In percents of (soft) max heap size.")                \
109           range(0,100)                                                      \
110                                                                             \
111   product(uintx, ShenandoahMinFreeThreshold, 10, EXPERIMENTAL,              \
112           "Percentage of free heap memory below which most heuristics "     \
113           "trigger collection independent of other triggers. Provides "     \
114           "a safety margin for many heuristics. In percents of (soft) "     \
115           "max heap size.")                                                 \
116           range(0,100)                                                      \
117                                                                             \
118   product(uintx, ShenandoahAllocationThreshold, 0, EXPERIMENTAL,            \
119           "How many new allocations should happen since the last GC cycle " \
120           "before some heuristics trigger the collection. In percents of "  \
121           "(soft) max heap size. Set to zero to effectively disable.")      \
122           range(0,100)                                                      \
123                                                                             \
124   product(uintx, ShenandoahAllocSpikeFactor, 5, EXPERIMENTAL,               \
125           "How much of heap should some heuristics reserve for absorbing "  \
126           "the allocation spikes. Larger value wastes more memory in "      \
127           "non-emergency cases, but provides more safety in emergency "     \
128           "cases. In percents of (soft) max heap size.")                    \
129           range(0,100)                                                      \
130                                                                             \
131   product(uintx, ShenandoahLearningSteps, 5, EXPERIMENTAL,                  \
132           "The number of cycles some heuristics take to collect in order "  \
133           "to learn application and GC performance.")                       \
134           range(0,100)                                                      \
135                                                                             \

158   product(double, ShenandoahAdaptiveInitialSpikeThreshold, 1.8, EXPERIMENTAL, \
159           "If the most recently sampled allocation rate is more than "      \
160           "this many standard deviations away from the moving average, "    \
161           "then a cycle is initiated. This value controls how sensitive "   \
162           "the heuristic is to allocation spikes. Decreasing this number "  \
163           "increases the sensitivity. ")                                    \
164                                                                             \
165   product(double, ShenandoahAdaptiveDecayFactor, 0.5, EXPERIMENTAL,         \
166           "The decay factor (alpha) used for values in the weighted "       \
167           "moving average of cycle time and allocation rate. "              \
168           "Larger values give more weight to recent values.")               \
169           range(0,1.0)                                                      \
170                                                                             \
171   product(uintx, ShenandoahGuaranteedGCInterval, 5*60*1000, EXPERIMENTAL,   \
172           "Many heuristics would guarantee a concurrent GC cycle at "       \
173           "least with this interval. This is useful when large idle "       \
174           "intervals are present, where GC can run without stealing "       \
175           "time from active application. Time is in milliseconds. "         \
176           "Setting this to 0 disables the feature.")                        \
177                                                                             \
178   product(uintx, ShenandoahGuaranteedOldGCInterval, 10*60*1000,  EXPERIMENTAL,  \
179           "Run a collection of the old generation at least this often. "    \
180           "Heuristics may trigger collections more frequently. Time is in " \
181           "milliseconds. Setting this to 0 disables the feature.")          \
182                                                                             \
183   product(bool, ShenandoahAlwaysClearSoftRefs, false, EXPERIMENTAL,         \
184           "Unconditionally clear soft references, instead of using any "    \
185           "other cleanup policy. This minimizes footprint at expense of"    \
186           "more soft reference churn in applications.")                     \
187                                                                             \
188   product(bool, ShenandoahUncommit, true, EXPERIMENTAL,                     \
189           "Allow to uncommit memory under unused regions and metadata. "    \
190           "This optimizes footprint at expense of allocation latency in "   \
191           "regions that require committing back. Uncommits would be "       \
192           "disabled by some heuristics, or with static heap size.")         \
193                                                                             \
194   product(uintx, ShenandoahUncommitDelay, 5*60*1000, EXPERIMENTAL,          \
195           "Uncommit memory for regions that were not used for more than "   \
196           "this time. First use after that would incur allocation stalls. " \
197           "Actively used regions would never be uncommitted, because they " \
198           "do not become unused longer than this delay. Time is in "        \
199           "milliseconds. Setting this delay to 0 effectively uncommits "    \
200           "regions almost immediately after they become unused.")           \
201                                                                             \
202   product(bool, ShenandoahRegionSampling, false, EXPERIMENTAL,              \
203           "Provide heap region sampling data via jvmstat.")                 \
204                                                                             \
205   product(int, ShenandoahRegionSamplingRate, 40, EXPERIMENTAL,              \
206           "Sampling rate for heap region sampling. In milliseconds between "\
207           "the samples. Higher values provide more fidelity, at expense "   \
208           "of more sampling overhead.")                                     \
209                                                                             \
210   product(bool, ShenandoahLogRegionSampling, false,                         \
211           "Save region sampling stream to ShenandoahRegionSamplingFile")    \
212                                                                             \
213   product(ccstr, ShenandoahRegionSamplingFile,                              \
214           "./shenandoahSnapshots_pid%p.log",                                \
215           "If ShenandoahLogRegionSampling is on, save sampling data stream "\
216           "to this file [default: ./shenandoahSnapshots_pid%p.log] "        \
217           "(%p replaced with pid)")                                         \
218                                                                             \
219   product(uintx, ShenandoahControlIntervalMin, 1, EXPERIMENTAL,             \
220           "The minimum sleep interval for the control loop that drives "    \
221           "the cycles. Lower values would increase GC responsiveness "      \
222           "to changing heap conditions, at the expense of higher perf "     \
223           "overhead. Time is in milliseconds.")                             \
224                                                                             \
225   product(uintx, ShenandoahControlIntervalMax, 10, EXPERIMENTAL,            \
226           "The maximum sleep interval for control loop that drives "        \
227           "the cycles. Lower values would increase GC responsiveness "      \
228           "to changing heap conditions, at the expense of higher perf "     \
229           "overhead. Time is in milliseconds.")                             \
230                                                                             \
231   product(uintx, ShenandoahControlIntervalAdjustPeriod, 1000, EXPERIMENTAL, \
232           "The time period for one step in control loop interval "          \
233           "adjustment. Lower values make adjustments faster, at the "       \
234           "expense of higher perf overhead. Time is in milliseconds.")      \
235                                                                             \
236   product(bool, ShenandoahVerify, false, DIAGNOSTIC,                        \
237           "Enable internal verification. This would catch many GC bugs, "   \
238           "but it would also stall the collector during the verification, " \
239           "which prolongs the pauses and might hide other bugs.")           \
240                                                                             \
241   product(intx, ShenandoahVerifyLevel, 4, DIAGNOSTIC,                       \
242           "Verification level, higher levels check more, taking more time. "\
243           "Accepted values are:"                                            \
244           " 0 = basic heap checks; "                                        \
245           " 1 = previous level, plus basic region checks; "                 \
246           " 2 = previous level, plus all roots; "                           \
247           " 3 = previous level, plus all reachable objects; "               \
248           " 4 = previous level, plus all marked objects")                   \
249                                                                             \
250   product(bool, ShenandoahElasticTLAB, true, DIAGNOSTIC,                    \
251           "Use Elastic TLABs with Shenandoah")                              \
252                                                                             \
253   product(bool, ShenandoahUsePLAB, true, DIAGNOSTIC,                        \
254           "Use PLABs for object promotions with Shenandoah, "               \
255           "if in generational mode and UseTLAB is also set.")               \
256                                                                             \
257   product(uintx, ShenandoahEvacReserve, 5, EXPERIMENTAL,                    \
258           "How much of heap to reserve for evacuations. Larger values make "\
259           "GC evacuate more live objects on every cycle, while leaving "    \
260           "less headroom for application to allocate in. In percents of "   \
261           "total heap size.")                                               \
262           range(1,100)                                                      \
263                                                                             \
264   product(double, ShenandoahEvacWaste, 1.2, EXPERIMENTAL,                   \
265           "How much waste evacuations produce within the reserved space. "  \
266           "Larger values make evacuations more resilient against "          \
267           "evacuation conflicts, at expense of evacuating less on each "    \
268           "GC cycle.")                                                      \
269           range(1.0,100.0)                                                  \
270                                                                             \
271   product(bool, ShenandoahEvacReserveOverflow, true, EXPERIMENTAL,          \
272           "Allow evacuations to overflow the reserved space. Enabling it "  \
273           "will make evacuations more resilient when evacuation "           \
274           "reserve/waste is incorrect, at the risk that application "       \
275           "runs out of memory too early.")                                  \
276                                                                             \
277   product(double, ShenandoahOldEvacReserve, 5.0, EXPERIMENTAL,              \
278           "How much of old generation to withhold from evacuations. "       \
279            "Larger values will result in fewer live objects being "         \
280            "evacuated in the old generation.")                              \
281           range(1,100)                                                      \
282                                                                             \
283   product(bool, ShenandoahPacing, true, EXPERIMENTAL,                       \
284           "Pace application allocations to give GC chance to start "        \
285           "and complete before allocation failure is reached.")             \
286                                                                             \
287   product(uintx, ShenandoahPacingMaxDelay, 10, EXPERIMENTAL,                \
288           "Max delay for pacing application allocations. Larger values "    \
289           "provide more resilience against out of memory, at expense at "   \
290           "hiding the GC latencies in the allocation path. Time is in "     \
291           "milliseconds. Setting it to arbitrarily large value makes "      \
292           "GC effectively stall the threads indefinitely instead of going " \
293           "to degenerated or Full GC.")                                     \
294                                                                             \
295   product(uintx, ShenandoahPacingIdleSlack, 2, EXPERIMENTAL,                \
296           "How much of heap counted as non-taxable allocations during idle "\
297           "phases. Larger value makes the pacing milder when collector is " \
298           "idle, requiring less rendezvous with control thread. Lower "     \
299           "value makes the pacing control less responsive to out-of-cycle " \
300           "allocs. In percent of total heap size.")                         \
301           range(0, 100)                                                     \
302                                                                             \

386   product(bool, ShenandoahCloneBarrier, true, DIAGNOSTIC,                   \
387           "Turn on/off clone barriers in Shenandoah")                       \
388                                                                             \
389   product(bool, ShenandoahLoadRefBarrier, true, DIAGNOSTIC,                 \
390           "Turn on/off load-reference barriers in Shenandoah")              \
391                                                                             \
392   product(bool, ShenandoahNMethodBarrier, true, DIAGNOSTIC,                 \
393           "Turn on/off NMethod entry barriers in Shenandoah")               \
394                                                                             \
395   product(bool, ShenandoahStackWatermarkBarrier, true, DIAGNOSTIC,          \
396           "Turn on/off stack watermark barriers in Shenandoah")             \
397                                                                             \
398   develop(bool, ShenandoahVerifyOptoBarriers, false,                        \
399           "Verify no missing barriers in C2.")                              \
400                                                                             \
401   product(bool, ShenandoahLoopOptsAfterExpansion, true, DIAGNOSTIC,         \
402           "Attempt more loop opts after barrier expansion.")                \
403                                                                             \
404   product(bool, ShenandoahSelfFixing, true, DIAGNOSTIC,                     \
405           "Fix references with load reference barrier. Disabling this "     \
406           "might degrade performance.")                                     \
407                                                                             \
408   product(uintx, ShenandoahTenuredRegionUsageBias, 192, EXPERIMENTAL,       \
409           "The collection set is comprised of heap regions that contain "   \
410           "the greatest amount of garbage.  "                               \
411           "For purposes of selecting regions to be included in the "        \
412           "collection set, regions that have reached the tenure age will "  \
413           "be treated as if their contained garbage is the actual "         \
414           "contained garbage multiplied by "                                \
415           "(ShenandoahTenuredRegionUsageBias / 128 (e.g. 150% for the "     \
416           "default value) as many times as the region's age meets or "      \
417           "exceeds the tenure age.  For example, if tenure age is 7, "      \
418           "the region age is 9, ShenandoahTenuredRegionUsageBias is "       \
419           "192, and the region is 12.5% garbage, this region "              \
420           "will by treated as if its garbage content is "                   \
421           "1/8 * 27/8 = 42.2% when comparing this region to untenured "     \
422           "regions.")                                                       \
423           range(128, 256)                                                   \
424                                                                             \
425   product(bool, ShenandoahPromoteTenuredObjects, true, DIAGNOSTIC,          \
426           "Turn on/off evacuating individual tenured young objects "        \
427           " to the old generation.")                                        \
428                                                                             \
429   product(bool, ShenandoahAllowOldMarkingPreemption, true, DIAGNOSTIC,      \
430           "Allow young generation collections to suspend concurrent"        \
431           " marking in the old generation.")                                \
432                                                                             \
433   product(uintx, ShenandoahAgingCyclePeriod, 1, EXPERIMENTAL,               \
434           "With generational mode, increment the age of objects and"        \
435           "regions each time this many young-gen GC cycles are completed.")
436  // end of GC_SHENANDOAH_FLAGS
437 
438 // 2^ShenandoahTenuredRegionUsageBiasLogBase2 is 128
439 #define ShenandoahTenuredRegionUsageBiasLogBase2 7
440 
441 #endif // SHARE_GC_SHENANDOAH_SHENANDOAH_GLOBALS_HPP
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