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

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  1 /*
  2  * Copyright (c) 2020, Oracle and/or its affiliates. All rights reserved.
  3  * Copyright (c) 2016, 2021, Red Hat, Inc. All rights reserved.

  4  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  5  *
  6  * This code is free software; you can redistribute it and/or modify it
  7  * under the terms of the GNU General Public License version 2 only, as
  8  * published by the Free Software Foundation.
  9  *
 10  * This code is distributed in the hope that it will be useful, but WITHOUT
 11  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 12  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 13  * version 2 for more details (a copy is included in the LICENSE file that
 14  * accompanied this code).
 15  *
 16  * You should have received a copy of the GNU General Public License version
 17  * 2 along with this work; if not, write to the Free Software Foundation,
 18  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 19  *
 20  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
 21  * or visit www.oracle.com if you need additional information or have any
 22  * questions.
 23  *
 24  */
 25 
 26 #ifndef SHARE_GC_SHENANDOAH_SHENANDOAH_GLOBALS_HPP
 27 #define SHARE_GC_SHENANDOAH_SHENANDOAH_GLOBALS_HPP
 28 
 29 #define GC_SHENANDOAH_FLAGS(develop,                                        \
 30                             develop_pd,                                     \
 31                             product,                                        \
 32                             product_pd,                                     \
 33                             notproduct,                                     \
 34                             range,                                          \
 35                             constraint)                                     \
 36                                                                             \
















































































 37   product(size_t, ShenandoahRegionSize, 0, EXPERIMENTAL,                    \
 38           "Static heap region size. Set zero to enable automatic sizing.")  \
 39                                                                             \
 40   product(size_t, ShenandoahTargetNumRegions, 2048, EXPERIMENTAL,           \
 41           "With automatic region sizing, this is the approximate number "   \
 42           "of regions that would be used, within min/max region size "      \
 43           "limits.")                                                        \
 44                                                                             \
 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                                                                             \
123   product(uintx, ShenandoahImmediateThreshold, 90, EXPERIMENTAL,            \
124           "The cycle may shortcut when enough garbage can be reclaimed "    \
125           "from the immediate garbage (completely garbage regions). "       \
126           "In percents of total garbage found. Setting this threshold "     \
127           "to 100 effectively disables the shortcut.")                      \
128           range(0,100)                                                      \
129                                                                             \
130   product(uintx, ShenandoahAdaptiveSampleFrequencyHz, 10, EXPERIMENTAL,     \
131           "The number of times per second to update the allocation rate "   \
132           "moving average.")                                                \
133                                                                             \
134   product(uintx, ShenandoahAdaptiveSampleSizeSeconds, 10, EXPERIMENTAL,     \
135           "The size of the moving window over which the average "           \
136           "allocation rate is maintained. The total number of samples "     \
137           "is the product of this number and the sample frequency.")        \
138                                                                             \
139   product(double, ShenandoahAdaptiveInitialConfidence, 1.8, EXPERIMENTAL,   \
140           "The number of standard deviations used to determine an initial " \
141           "margin of error for the average cycle time and average "         \
142           "allocation rate. Increasing this value will cause the "          \
143           "heuristic to initiate more concurrent cycles." )                 \
144                                                                             \
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,              \

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                                                                             \

300           "that progress is determined by ShenandoahCriticalFreeThreshold") \
301                                                                             \
302   product(bool, ShenandoahImplicitGCInvokesConcurrent, false, EXPERIMENTAL, \
303           "Should internally-caused GC requests invoke concurrent cycles, " \
304           "should they do the stop-the-world (Degenerated / Full GC)? "     \
305           "Many heuristics automatically enable this. This option is "      \
306           "similar to global ExplicitGCInvokesConcurrent.")                 \
307                                                                             \
308   product(bool, ShenandoahHumongousMoves, true, DIAGNOSTIC,                 \
309           "Allow moving humongous regions. This makes GC more resistant "   \
310           "to external fragmentation that may otherwise fail other "        \
311           "humongous allocations, at the expense of higher GC copying "     \
312           "costs. Currently affects stop-the-world (Full) cycle only.")     \
313                                                                             \
314   product(bool, ShenandoahOOMDuringEvacALot, false, DIAGNOSTIC,             \
315           "Testing: simulate OOM during evacuation.")                       \
316                                                                             \
317   product(bool, ShenandoahAllocFailureALot, false, DIAGNOSTIC,              \
318           "Testing: make lots of artificial allocation failures.")          \
319                                                                             \









320   product(intx, ShenandoahMarkScanPrefetch, 32, EXPERIMENTAL,               \
321           "How many objects to prefetch ahead when traversing mark bitmaps."\
322           "Set to 0 to disable prefetching.")                               \
323           range(0, 256)                                                     \
324                                                                             \
325   product(uintx, ShenandoahMarkLoopStride, 1000, EXPERIMENTAL,              \
326           "How many items to process during one marking iteration before "  \
327           "checking for cancellation, yielding, etc. Larger values improve "\
328           "marking performance at expense of responsiveness.")              \
329                                                                             \
330   product(uintx, ShenandoahParallelRegionStride, 1024, EXPERIMENTAL,        \
331           "How many regions to process at once during parallel region "     \
332           "iteration. Affects heaps with lots of regions.")                 \
333                                                                             \
334   product(size_t, ShenandoahSATBBufferSize, 1 * K, EXPERIMENTAL,            \
335           "Number of entries in an SATB log buffer.")                       \
336           range(1, max_uintx)                                               \
337                                                                             \
338   product(uintx, ShenandoahMaxSATBBufferFlushes, 5, EXPERIMENTAL,           \
339           "How many times to maximum attempt to flush SATB buffers at the " \
340           "end of concurrent marking.")                                     \
341                                                                             \
342   product(bool, ShenandoahSuspendibleWorkers, true, EXPERIMENTAL,           \
343           "Suspend concurrent GC worker threads at safepoints")             \
344                                                                             \
345   product(bool, ShenandoahSATBBarrier, true, DIAGNOSTIC,                    \
346           "Turn on/off SATB barriers in Shenandoah")                        \
347                                                                             \
348   product(bool, ShenandoahIUBarrier, false, DIAGNOSTIC,                     \
349           "Turn on/off I-U barriers barriers in Shenandoah")                \
350                                                                             \




351   product(bool, ShenandoahCASBarrier, true, DIAGNOSTIC,                     \
352           "Turn on/off CAS barriers in Shenandoah")                         \
353                                                                             \
354   product(bool, ShenandoahCloneBarrier, true, DIAGNOSTIC,                   \
355           "Turn on/off clone barriers in Shenandoah")                       \
356                                                                             \
357   product(bool, ShenandoahLoadRefBarrier, true, DIAGNOSTIC,                 \
358           "Turn on/off load-reference barriers in Shenandoah")              \
359                                                                             \
360   product(bool, ShenandoahStackWatermarkBarrier, true, DIAGNOSTIC,          \
361           "Turn on/off stack watermark barriers in Shenandoah")             \
362                                                                             \
363   develop(bool, ShenandoahVerifyOptoBarriers, false,                        \
364           "Verify no missing barriers in C2.")                              \
365                                                                             \
366   product(bool, ShenandoahLoopOptsAfterExpansion, true, DIAGNOSTIC,         \
367           "Attempt more loop opts after barrier expansion.")                \
368                                                                             \
369   product(bool, ShenandoahSelfFixing, true, DIAGNOSTIC,                     \
370           "Fix references with load reference barrier. Disabling this "     \
371           "might degrade performance.")
372 
373 // end of GC_SHENANDOAH_FLAGS





















374 
375 #endif // SHARE_GC_SHENANDOAH_SHENANDOAH_GLOBALS_HPP

  1 /*
  2  * Copyright (c) 2020, 2023, Oracle and/or its affiliates. All rights reserved.
  3  * Copyright (c) 2016, 2021, Red Hat, Inc. All rights reserved.
  4  * Copyright Amazon.com Inc. or its affiliates. All Rights Reserved.
  5  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  6  *
  7  * This code is free software; you can redistribute it and/or modify it
  8  * under the terms of the GNU General Public License version 2 only, as
  9  * published by the Free Software Foundation.
 10  *
 11  * This code is distributed in the hope that it will be useful, but WITHOUT
 12  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 13  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 14  * version 2 for more details (a copy is included in the LICENSE file that
 15  * accompanied this code).
 16  *
 17  * You should have received a copy of the GNU General Public License version
 18  * 2 along with this work; if not, write to the Free Software Foundation,
 19  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 20  *
 21  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
 22  * or visit www.oracle.com if you need additional information or have any
 23  * questions.
 24  *
 25  */
 26 
 27 #ifndef SHARE_GC_SHENANDOAH_SHENANDOAH_GLOBALS_HPP
 28 #define SHARE_GC_SHENANDOAH_SHENANDOAH_GLOBALS_HPP
 29 
 30 #define GC_SHENANDOAH_FLAGS(develop,                                        \
 31                             develop_pd,                                     \
 32                             product,                                        \
 33                             product_pd,                                     \
 34                             notproduct,                                     \
 35                             range,                                          \
 36                             constraint)                                     \
 37                                                                             \
 38   product(uintx, ShenandoahGenerationalHumongousReserve, 0, EXPERIMENTAL,   \
 39           "(Generational mode only) What percent of the heap should be "    \
 40           "reserved for humongous objects if possible.  Old-generation "    \
 41           "collections will endeavor to evacuate old-gen regions within "   \
 42           "this reserved area even if these regions do not contain high "   \
 43           "percentage of garbage.  Setting a larger value will cause "      \
 44           "more frequent old-gen collections.  A smaller value will "       \
 45           "increase the likelihood that humongous object allocations "      \
 46           "fail, resulting in stop-the-world full GCs.")                    \
 47           range(0,100)                                                      \
 48                                                                             \
 49   product(double, ShenandoahMinOldGenGrowthPercent, 12.5, EXPERIMENTAL,     \
 50           "(Generational mode only) If the usage within old generation "    \
 51           "has grown by at least this percent of its live memory size "     \
 52           "at completion of the most recent old-generation marking "        \
 53           "effort, heuristics may trigger the start of a new old-gen "      \
 54           "collection.")                                                    \
 55           range(0.0,100.0)                                                  \
 56                                                                             \
 57   product(uintx, ShenandoahIgnoreOldGrowthBelowPercentage,10, EXPERIMENTAL, \
 58           "(Generational mode only) If the total usage of the old "         \
 59           "generation is smaller than this percent, we do not trigger "     \
 60           "old gen collections even if old has grown, except when "         \
 61           "ShenandoahGenerationalDoNotIgnoreGrowthAfterYoungCycles "        \
 62           "consecutive cycles have been completed following the "           \
 63           "preceding old-gen collection.")                                  \
 64           range(0,100)                                                      \
 65                                                                             \
 66   product(uintx, ShenandoahDoNotIgnoreGrowthAfterYoungCycles,               \
 67           50, EXPERIMENTAL,                                                 \
 68           "(Generational mode only) Even if the usage of old generation "   \
 69           "is below ShenandoahIgnoreOldGrowthBelowPercentage, "             \
 70           "trigger an old-generation mark if old has grown and this "       \
 71           "many consecutive young-gen collections have been "               \
 72           "completed following the preceding old-gen collection.")          \
 73                                                                             \
 74   product(bool, ShenandoahGenerationalCensusAtEvac, false, EXPERIMENTAL,    \
 75           "(Generational mode only) Object age census at evacuation, "      \
 76           "rather than during marking.")                                    \
 77                                                                             \
 78   product(bool, ShenandoahGenerationalAdaptiveTenuring, true, EXPERIMENTAL, \
 79           "(Generational mode only) Dynamically adapt tenuring age.")       \
 80                                                                             \
 81   product(bool, ShenandoahGenerationalCensusIgnoreOlderCohorts, true,       \
 82                                                                EXPERIMENTAL,\
 83           "(Generational mode only) Ignore mortality rates older than the " \
 84           "oldest cohort under the tenuring age for the last cycle." )      \
 85                                                                             \
 86   product(uintx, ShenandoahGenerationalMinTenuringAge, 1, EXPERIMENTAL,     \
 87           "(Generational mode only) Floor for adaptive tenuring age. "      \
 88           "Setting floor and ceiling to the same value fixes the tenuring " \
 89           "age; setting both to 1 simulates a poor approximation to "       \
 90           "AlwaysTenure, and setting both to 16 simulates NeverTenure.")    \
 91           range(1,16)                                                       \
 92                                                                             \
 93   product(uintx, ShenandoahGenerationalMaxTenuringAge, 15, EXPERIMENTAL,    \
 94           "(Generational mode only) Ceiling for adaptive tenuring age. "    \
 95           "Setting floor and ceiling to the same value fixes the tenuring " \
 96           "age; setting both to 1 simulates a poor approximation to "       \
 97           "AlwaysTenure, and setting both to 16 simulates NeverTenure.")    \
 98           range(1,16)                                                       \
 99                                                                             \
100   product(double, ShenandoahGenerationalTenuringMortalityRateThreshold,     \
101                                                          0.1, EXPERIMENTAL, \
102           "(Generational mode only) Cohort mortality rates below this "     \
103           "value will be treated as indicative of longevity, leading to "   \
104           "tenuring. A lower value delays tenuring, a higher value hastens "\
105           "it. Used only when ShenandoahGenerationalhenAdaptiveTenuring is "\
106           "enabled.")                                                       \
107           range(0.001,0.999)                                                \
108                                                                             \
109   product(size_t, ShenandoahGenerationalTenuringCohortPopulationThreshold,  \
110                                                          4*K, EXPERIMENTAL, \
111           "(Generational mode only) Cohorts whose population is lower than "\
112           "this value in the previous census are ignored wrt tenuring "     \
113           "decisions. Effectively this makes then tenurable as soon as all "\
114           "older cohorts are. Set this value to the largest cohort "        \
115           "population volume that you are comfortable ignoring when making "\
116           "tenuring decisions.")                                            \
117                                                                             \
118   product(size_t, ShenandoahRegionSize, 0, EXPERIMENTAL,                    \
119           "Static heap region size. Set zero to enable automatic sizing.")  \
120                                                                             \
121   product(size_t, ShenandoahTargetNumRegions, 2048, EXPERIMENTAL,           \
122           "With automatic region sizing, this is the approximate number "   \
123           "of regions that would be used, within min/max region size "      \
124           "limits.")                                                        \
125                                                                             \
126   product(size_t, ShenandoahMinRegionSize, 256 * K, EXPERIMENTAL,           \
127           "With automatic region sizing, the regions would be at least "    \
128           "this large.")                                                    \
129                                                                             \
130   product(size_t, ShenandoahMaxRegionSize, 32 * M, EXPERIMENTAL,            \
131           "With automatic region sizing, the regions would be at most "     \
132           "this large.")                                                    \
133                                                                             \
134   product(intx, ShenandoahHumongousThreshold, 100, EXPERIMENTAL,            \
135           "Humongous objects are allocated in separate regions. "           \
136           "This setting defines how large the object should be to be "      \
137           "deemed humongous. Value is in  percents of heap region size. "   \
138           "This also caps the maximum TLAB size.")                          \
139           range(1, 100)                                                     \
140                                                                             \
141   product(ccstr, ShenandoahGCMode, "satb",                                  \
142           "GC mode to use.  Among other things, this defines which "        \
143           "barriers are in in use. Possible values are:"                    \
144           " satb - snapshot-at-the-beginning concurrent GC (three pass mark-evac-update);"  \
145           " iu - incremental-update concurrent GC (three pass mark-evac-update);"  \
146           " passive - stop the world GC only (either degenerated or full);" \
147           " generational - generational concurrent GC")                     \
148                                                                             \
149   product(ccstr, ShenandoahGCHeuristics, "adaptive",                        \
150           "GC heuristics to use. This fine-tunes the GC mode selected, "    \
151           "by choosing when to start the GC, how much to process on each "  \
152           "cycle, and what other features to automatically enable. "        \
153           "Possible values are:"                                            \
154           " adaptive - adapt to maintain the given amount of free heap "    \
155           "at all times, even during the GC cycle;"                         \
156           " static -  trigger GC when free heap falls below the threshold;" \
157           " aggressive - run GC continuously, try to evacuate everything;"  \
158           " compact - run GC more frequently and with deeper targets to "   \
159           "free up more memory.")                                           \
160                                                                             \
161   product(uintx, ShenandoahExpeditePromotionsThreshold, 5, EXPERIMENTAL,    \
162           "When Shenandoah expects to promote at least this percentage "    \
163           "of the young generation, trigger a young collection to "         \
164           "expedite these promotions.")                                     \
165           range(0,100)                                                      \
166                                                                             \
167   product(uintx, ShenandoahExpediteMixedThreshold, 10, EXPERIMENTAL,        \
168           "When there are this many old regions waiting to be collected, "  \
169           "trigger a mixed collection immediately.")                        \
170                                                                             \
171   product(uintx, ShenandoahUnloadClassesFrequency, 1, EXPERIMENTAL,         \
172           "Unload the classes every Nth cycle. Normally affects concurrent "\
173           "GC cycles, as degenerated and full GCs would try to unload "     \
174           "classes regardless. Set to zero to disable class unloading.")    \
175                                                                             \
176   product(uintx, ShenandoahGarbageThreshold, 25, EXPERIMENTAL,              \
177           "How much garbage a region has to contain before it would be "    \
178           "taken for collection. This a guideline only, as GC heuristics "  \
179           "may select the region for collection even if it has little "     \
180           "garbage. This also affects how much internal fragmentation the " \
181           "collector accepts. In percents of heap region size.")            \
182           range(0,100)                                                      \
183                                                                             \
184   product(uintx, ShenandoahOldGarbageThreshold, 15, EXPERIMENTAL,           \
185           "How much garbage an old region has to contain before it would "  \
186           "be taken for collection.")                                       \
187           range(0,100)                                                      \
188                                                                             \
189   product(uintx, ShenandoahIgnoreGarbageThreshold, 5, EXPERIMENTAL,         \
190           "When less than this amount of garbage (as a percentage of "      \
191           "region size) exists within a region, the region will not be "    \
192           "added to the collection set, even when the heuristic has "       \
193           "chosen to aggressively add regions with less than "              \
194           "ShenandoahGarbageThreshold amount of garbage into the "          \
195           "collection set.")                                                \
196           range(0,100)                                                      \
197                                                                             \
198   product(uintx, ShenandoahInitFreeThreshold, 70, EXPERIMENTAL,             \
199           "When less than this amount of memory is free within the"         \
200           "heap or generation, trigger a learning cycle if we are "         \
201           "in learning mode.  Learning mode happens during initialization " \
202           "and following a drastic state change, such as following a "      \
203           "degenerated or Full GC cycle.  In percents of soft max "         \
204           "heap size.")                                                     \
205           range(0,100)                                                      \
206                                                                             \
207   product(uintx, ShenandoahMinFreeThreshold, 10, EXPERIMENTAL,              \
208           "Percentage of free heap memory (or young generation, in "        \
209           "generational mode) below which most heuristics trigger "         \
210           "collection independent of other triggers. Provides a safety "    \
211           "margin for many heuristics. In percents of (soft) max heap "     \
212           "size.")                                                          \
213           range(0,100)                                                      \
214                                                                             \
215   product(uintx, ShenandoahAllocationThreshold, 0, EXPERIMENTAL,            \
216           "How many new allocations should happen since the last GC cycle " \
217           "before some heuristics trigger the collection. In percents of "  \
218           "(soft) max heap size. Set to zero to effectively disable.")      \
219           range(0,100)                                                      \
220                                                                             \
221   product(uintx, ShenandoahAllocSpikeFactor, 5, EXPERIMENTAL,               \
222           "How much of heap should some heuristics reserve for absorbing "  \
223           "the allocation spikes. Larger value wastes more memory in "      \
224           "non-emergency cases, but provides more safety in emergency "     \
225           "cases. In percents of (soft) max heap size.")                    \
226           range(0,100)                                                      \
227                                                                             \
228   product(uintx, ShenandoahLearningSteps, 10, EXPERIMENTAL,                 \
229           "The number of cycles some heuristics take to collect in order "  \
230           "to learn application and GC performance.")                       \
231           range(0,100)                                                      \
232                                                                             \
233   product(uintx, ShenandoahImmediateThreshold, 70, EXPERIMENTAL,            \
234           "The cycle may shortcut when enough garbage can be reclaimed "    \
235           "from the immediate garbage (completely garbage regions). "       \
236           "In percents of total garbage found. Setting this threshold "     \
237           "to 100 effectively disables the shortcut.")                      \
238           range(0,100)                                                      \
239                                                                             \
240   product(uintx, ShenandoahAdaptiveSampleFrequencyHz, 10, EXPERIMENTAL,     \
241           "The number of times per second to update the allocation rate "   \
242           "moving average.")                                                \
243                                                                             \
244   product(uintx, ShenandoahAdaptiveSampleSizeSeconds, 10, EXPERIMENTAL,     \
245           "The size of the moving window over which the average "           \
246           "allocation rate is maintained. The total number of samples "     \
247           "is the product of this number and the sample frequency.")        \
248                                                                             \
249   product(double, ShenandoahAdaptiveInitialConfidence, 1.8, EXPERIMENTAL,   \
250           "The number of standard deviations used to determine an initial " \
251           "margin of error for the average cycle time and average "         \
252           "allocation rate. Increasing this value will cause the "          \
253           "heuristic to initiate more concurrent cycles." )                 \
254                                                                             \
255   product(double, ShenandoahAdaptiveInitialSpikeThreshold, 1.8, EXPERIMENTAL, \
256           "If the most recently sampled allocation rate is more than "      \
257           "this many standard deviations away from the moving average, "    \
258           "then a cycle is initiated. This value controls how sensitive "   \
259           "the heuristic is to allocation spikes. Decreasing this number "  \
260           "increases the sensitivity. ")                                    \
261                                                                             \
262   product(double, ShenandoahAdaptiveDecayFactor, 0.1, EXPERIMENTAL,         \
263           "The decay factor (alpha) used for values in the weighted "       \
264           "moving average of cycle time and allocation rate. "              \
265           "Larger values give more weight to recent values.")               \
266           range(0,1.0)                                                      \
267                                                                             \
268   product(bool, ShenandoahAdaptiveIgnoreShortCycles, true, EXPERIMENTAL,    \
269           "The adaptive heuristic tracks a moving average of cycle "        \
270           "times in order to start a gc before memory is exhausted. "       \
271           "In some cases, Shenandoah may skip the evacuation and update "   \
272           "reference phases, resulting in a shorter cycle. These may skew " \
273           "the average cycle time downward and may cause the heuristic "    \
274           "to wait too long to start a cycle. Disabling this will have "    \
275           "the gc run less often, which will reduce CPU utilization, but"   \
276           "increase the risk of degenerated cycles.")                       \
277                                                                             \
278   product(uintx, ShenandoahGuaranteedGCInterval, 5*60*1000, EXPERIMENTAL,   \
279           "Many heuristics would guarantee a concurrent GC cycle at "       \
280           "least with this interval. This is useful when large idle "       \
281           "intervals are present, where GC can run without stealing "       \
282           "time from active application. Time is in milliseconds. "         \
283           "Setting this to 0 disables the feature.")                        \
284                                                                             \
285   product(uintx, ShenandoahGuaranteedOldGCInterval, 10*60*1000, EXPERIMENTAL, \
286           "Run a collection of the old generation at least this often. "    \
287           "Heuristics may trigger collections more frequently. Time is in " \
288           "milliseconds. Setting this to 0 disables the feature.")          \
289                                                                             \
290   product(uintx, ShenandoahGuaranteedYoungGCInterval, 5*60*1000,  EXPERIMENTAL,  \
291           "Run a collection of the young generation at least this often. "  \
292           "Heuristics may trigger collections more frequently. Time is in " \
293           "milliseconds. Setting this to 0 disables the feature.")          \
294                                                                             \
295   product(bool, ShenandoahAlwaysClearSoftRefs, false, EXPERIMENTAL,         \
296           "Unconditionally clear soft references, instead of using any "    \
297           "other cleanup policy. This minimizes footprint at expense of"    \
298           "more soft reference churn in applications.")                     \
299                                                                             \
300   product(bool, ShenandoahUncommit, true, EXPERIMENTAL,                     \
301           "Allow to uncommit memory under unused regions and metadata. "    \
302           "This optimizes footprint at expense of allocation latency in "   \
303           "regions that require committing back. Uncommits would be "       \
304           "disabled by some heuristics, or with static heap size.")         \
305                                                                             \
306   product(uintx, ShenandoahUncommitDelay, 5*60*1000, EXPERIMENTAL,          \
307           "Uncommit memory for regions that were not used for more than "   \
308           "this time. First use after that would incur allocation stalls. " \
309           "Actively used regions would never be uncommitted, because they " \
310           "do not become unused longer than this delay. Time is in "        \
311           "milliseconds. Setting this delay to 0 effectively uncommits "    \
312           "regions almost immediately after they become unused.")           \
313                                                                             \
314   product(bool, ShenandoahRegionSampling, false, EXPERIMENTAL,              \

334   product(uintx, ShenandoahControlIntervalAdjustPeriod, 1000, EXPERIMENTAL, \
335           "The time period for one step in control loop interval "          \
336           "adjustment. Lower values make adjustments faster, at the "       \
337           "expense of higher perf overhead. Time is in milliseconds.")      \
338                                                                             \
339   product(bool, ShenandoahVerify, false, DIAGNOSTIC,                        \
340           "Enable internal verification. This would catch many GC bugs, "   \
341           "but it would also stall the collector during the verification, " \
342           "which prolongs the pauses and might hide other bugs.")           \
343                                                                             \
344   product(intx, ShenandoahVerifyLevel, 4, DIAGNOSTIC,                       \
345           "Verification level, higher levels check more, taking more time. "\
346           "Accepted values are:"                                            \
347           " 0 = basic heap checks; "                                        \
348           " 1 = previous level, plus basic region checks; "                 \
349           " 2 = previous level, plus all roots; "                           \
350           " 3 = previous level, plus all reachable objects; "               \
351           " 4 = previous level, plus all marked objects")                   \
352                                                                             \
353   product(bool, ShenandoahElasticTLAB, true, DIAGNOSTIC,                    \
354           "Use Elastic TLABs with Shenandoah. This allows Shenandoah to "   \
355           "decrease the size of a TLAB to fit in a region's remaining space") \
356                                                                             \
357   product(uintx, ShenandoahEvacReserve, 5, EXPERIMENTAL,                    \
358           "How much of (young-generation) heap to reserve for "             \
359           "(young-generation) evacuations.  Larger values allow GC to "     \
360           "evacuate more live objects on every cycle, while leaving "       \
361           "less headroom for application to allocate while GC is "          \
362           "evacuating and updating references. This parameter is "          \
363           "consulted at the end of marking, before selecting the "          \
364           "collection set.  If available memory at this time is smaller "   \
365           "than the indicated reserve, the bound on collection set size is "\
366           "adjusted downward.  The size of a generational mixed "           \
367           "evacuation collection set (comprised of both young and old "     \
368           "regions) is also bounded by this parameter.  In percents of "    \
369           "total (young-generation) heap size.")                            \
370           range(1,100)                                                      \
371                                                                             \
372   product(double, ShenandoahEvacWaste, 1.2, EXPERIMENTAL,                   \
373           "How much waste evacuations produce within the reserved space. "  \
374           "Larger values make evacuations more resilient against "          \
375           "evacuation conflicts, at expense of evacuating less on each "    \
376           "GC cycle.  Smaller values increase the risk of evacuation "      \
377           "failures, which will trigger stop-the-world Full GC passes.")    \
378           range(1.0,100.0)                                                  \
379                                                                             \
380   product(double, ShenandoahOldEvacWaste, 1.4, EXPERIMENTAL,                \
381           "How much waste evacuations produce within the reserved space. "  \
382           "Larger values make evacuations more resilient against "          \
383           "evacuation conflicts, at expense of evacuating less on each "    \
384           "GC cycle.  Smaller values increase the risk of evacuation "      \
385           "failures, which will trigger stop-the-world Full GC passes.")    \
386           range(1.0,100.0)                                                  \
387                                                                             \
388   product(double, ShenandoahPromoEvacWaste, 1.2, EXPERIMENTAL,              \
389           "How much waste promotions produce within the reserved space. "   \
390           "Larger values make evacuations more resilient against "          \
391           "evacuation conflicts, at expense of promoting less on each "     \
392           "GC cycle.  Smaller values increase the risk of evacuation "      \
393           "failures, which will trigger stop-the-world Full GC passes.")    \
394           range(1.0,100.0)                                                  \
395                                                                             \
396   product(uintx, ShenandoahMaxEvacLABRatio, 0, EXPERIMENTAL,                \
397           "Potentially, each running thread maintains a PLAB for "          \
398           "evacuating objects into old-gen memory and a GCLAB for "         \
399           "evacuating objects into young-gen memory.  Each time a thread "  \
400           "exhausts its PLAB or GCLAB, a new local buffer is allocated. "   \
401           "By default, the new buffer is twice the size of the previous "   \
402           "buffer.  The sizes are reset to the minimum at the start of "    \
403           "each GC pass.  This parameter limits the growth of evacuation "  \
404           "buffer sizes to its value multiplied by the minimum buffer "     \
405           "size.  A higher value allows evacuation allocations to be more " \
406           "efficient because less synchronization is required by "          \
407           "individual threads.  However, a larger value increases the "     \
408           "likelihood of evacuation failures, leading to long "             \
409           "stop-the-world pauses.  This is because a large value "          \
410           "allows individual threads to consume large percentages of "      \
411           "the total evacuation budget without necessarily effectively "    \
412           "filling their local evacuation buffers with evacuated "          \
413           "objects.  A value of zero means no maximum size is enforced.")   \
414           range(0, 1024)                                                    \
415                                                                             \
416   product(bool, ShenandoahEvacReserveOverflow, true, EXPERIMENTAL,          \
417           "Allow evacuations to overflow the reserved space. Enabling it "  \
418           "will make evacuations more resilient when evacuation "           \
419           "reserve/waste is incorrect, at the risk that application "       \
420           "runs out of memory too early.")                                  \
421                                                                             \
422   product(uintx, ShenandoahOldEvacRatioPercent, 75, EXPERIMENTAL,           \
423           "The maximum proportion of evacuation from old-gen memory, as "   \
424           "a percent ratio.  The default value 75 denotes that no more "    \
425           "than 75% of the collection set evacuation "                      \
426           "workload may be evacuate to old-gen heap regions.  This limits " \
427           "both the promotion of aged regions and the compaction of "       \
428           "existing old regions.  A value of 75 denotes that the normal "   \
429           "young-gen evacuation is increased by up to four fold. "          \
430           "A larger value allows quicker promotion and allows"              \
431           "a smaller number of mixed evacuations to process "               \
432           "the entire list of old-gen collection candidates at the cost "   \
433           "of an increased disruption of the normal cadence of young-gen "  \
434           "collections.  A value of 100 allows a mixed evacuation to "      \
435           "focus entirely on old-gen memory, allowing no young-gen "        \
436           "regions to be collected, likely resulting in subsequent "        \
437           "allocation failures because the allocation pool is not "         \
438           "replenished.  A value of 0 allows a mixed evacuation to"         \
439           "focus entirely on young-gen memory, allowing no old-gen "        \
440           "regions to be collected, likely resulting in subsequent "        \
441           "promotion failures and triggering of stop-the-world full GC "    \
442           "events.")                                                        \
443           range(0,100)                                                      \
444                                                                             \
445   product(uintx, ShenandoahMinYoungPercentage, 20, EXPERIMENTAL,            \
446           "The minimum percentage of the heap to use for the young "        \
447           "generation. Heuristics will not adjust the young generation "    \
448           "to be less than this.")                                          \
449           range(0, 100)                                                     \
450                                                                             \
451   product(uintx, ShenandoahMaxYoungPercentage, 100, EXPERIMENTAL,           \
452           "The maximum percentage of the heap to use for the young "        \
453           "generation. Heuristics will not adjust the young generation "    \
454           "to be more than this.")                                          \
455           range(0, 100)                                                     \
456                                                                             \
457   product(bool, ShenandoahPacing, true, EXPERIMENTAL,                       \
458           "Pace application allocations to give GC chance to start "        \
459           "and complete before allocation failure is reached.")             \
460                                                                             \
461   product(uintx, ShenandoahPacingMaxDelay, 10, EXPERIMENTAL,                \
462           "Max delay for pacing application allocations. Larger values "    \
463           "provide more resilience against out of memory, at expense at "   \
464           "hiding the GC latencies in the allocation path. Time is in "     \
465           "milliseconds. Setting it to arbitrarily large value makes "      \
466           "GC effectively stall the threads indefinitely instead of going " \
467           "to degenerated or Full GC.")                                     \
468                                                                             \
469   product(uintx, ShenandoahPacingIdleSlack, 2, EXPERIMENTAL,                \
470           "How much of heap counted as non-taxable allocations during idle "\
471           "phases. Larger value makes the pacing milder when collector is " \
472           "idle, requiring less rendezvous with control thread. Lower "     \
473           "value makes the pacing control less responsive to out-of-cycle " \
474           "allocs. In percent of total heap size.")                         \
475           range(0, 100)                                                     \
476                                                                             \

511           "that progress is determined by ShenandoahCriticalFreeThreshold") \
512                                                                             \
513   product(bool, ShenandoahImplicitGCInvokesConcurrent, false, EXPERIMENTAL, \
514           "Should internally-caused GC requests invoke concurrent cycles, " \
515           "should they do the stop-the-world (Degenerated / Full GC)? "     \
516           "Many heuristics automatically enable this. This option is "      \
517           "similar to global ExplicitGCInvokesConcurrent.")                 \
518                                                                             \
519   product(bool, ShenandoahHumongousMoves, true, DIAGNOSTIC,                 \
520           "Allow moving humongous regions. This makes GC more resistant "   \
521           "to external fragmentation that may otherwise fail other "        \
522           "humongous allocations, at the expense of higher GC copying "     \
523           "costs. Currently affects stop-the-world (Full) cycle only.")     \
524                                                                             \
525   product(bool, ShenandoahOOMDuringEvacALot, false, DIAGNOSTIC,             \
526           "Testing: simulate OOM during evacuation.")                       \
527                                                                             \
528   product(bool, ShenandoahAllocFailureALot, false, DIAGNOSTIC,              \
529           "Testing: make lots of artificial allocation failures.")          \
530                                                                             \
531   product(uintx, ShenandoahCoalesceChance, 0, DIAGNOSTIC,                   \
532           "Testing: Abandon remaining mixed collections with this "         \
533           "likelihood. Following each mixed collection, abandon all "       \
534           "remaining mixed collection candidate regions with likelihood "   \
535           "ShenandoahCoalesceChance. Abandoning a mixed collection will "   \
536           "cause the old regions to be made parsable, rather than being "   \
537           "evacuated.")                                                     \
538           range(0, 100)                                                     \
539                                                                             \
540   product(intx, ShenandoahMarkScanPrefetch, 32, EXPERIMENTAL,               \
541           "How many objects to prefetch ahead when traversing mark bitmaps."\
542           "Set to 0 to disable prefetching.")                               \
543           range(0, 256)                                                     \
544                                                                             \
545   product(uintx, ShenandoahMarkLoopStride, 1000, EXPERIMENTAL,              \
546           "How many items to process during one marking iteration before "  \
547           "checking for cancellation, yielding, etc. Larger values improve "\
548           "marking performance at expense of responsiveness.")              \
549                                                                             \
550   product(uintx, ShenandoahParallelRegionStride, 1024, EXPERIMENTAL,        \
551           "How many regions to process at once during parallel region "     \
552           "iteration. Affects heaps with lots of regions.")                 \
553                                                                             \
554   product(size_t, ShenandoahSATBBufferSize, 1 * K, EXPERIMENTAL,            \
555           "Number of entries in an SATB log buffer.")                       \
556           range(1, max_uintx)                                               \
557                                                                             \
558   product(uintx, ShenandoahMaxSATBBufferFlushes, 5, EXPERIMENTAL,           \
559           "How many times to maximum attempt to flush SATB buffers at the " \
560           "end of concurrent marking.")                                     \
561                                                                             \
562   product(bool, ShenandoahSuspendibleWorkers, true, EXPERIMENTAL,           \
563           "Suspend concurrent GC worker threads at safepoints")             \
564                                                                             \
565   product(bool, ShenandoahSATBBarrier, true, DIAGNOSTIC,                    \
566           "Turn on/off SATB barriers in Shenandoah")                        \
567                                                                             \
568   product(bool, ShenandoahIUBarrier, false, DIAGNOSTIC,                     \
569           "Turn on/off I-U barriers barriers in Shenandoah")                \
570                                                                             \
571   product(bool, ShenandoahCardBarrier, false, DIAGNOSTIC,                   \
572           "Turn on/off card-marking post-write barrier in Shenandoah: "     \
573           " true when ShenandoahGCMode is generational, false otherwise")   \
574                                                                             \
575   product(bool, ShenandoahCASBarrier, true, DIAGNOSTIC,                     \
576           "Turn on/off CAS barriers in Shenandoah")                         \
577                                                                             \
578   product(bool, ShenandoahCloneBarrier, true, DIAGNOSTIC,                   \
579           "Turn on/off clone barriers in Shenandoah")                       \
580                                                                             \
581   product(bool, ShenandoahLoadRefBarrier, true, DIAGNOSTIC,                 \
582           "Turn on/off load-reference barriers in Shenandoah")              \
583                                                                             \
584   product(bool, ShenandoahStackWatermarkBarrier, true, DIAGNOSTIC,          \
585           "Turn on/off stack watermark barriers in Shenandoah")             \
586                                                                             \
587   develop(bool, ShenandoahVerifyOptoBarriers, false,                        \
588           "Verify no missing barriers in C2.")                              \
589                                                                             \
590   product(bool, ShenandoahLoopOptsAfterExpansion, true, DIAGNOSTIC,         \
591           "Attempt more loop opts after barrier expansion.")                \
592                                                                             \
593   product(bool, ShenandoahSelfFixing, true, DIAGNOSTIC,                     \
594           "Fix references with load reference barrier. Disabling this "     \
595           "might degrade performance.")                                     \
596                                                                             \
597   product(uintx, ShenandoahOldCompactionReserve, 8, EXPERIMENTAL,           \
598           "During generational GC, prevent promotions from filling "        \
599           "this number of heap regions.  These regions are reserved "       \
600           "for the purpose of supporting compaction of old-gen "            \
601           "memory.  Otherwise, old-gen memory cannot be compacted.")        \
602           range(0, 128)                                                     \
603                                                                             \
604   product(bool, ShenandoahAllowOldMarkingPreemption, true, DIAGNOSTIC,      \
605           "Allow young generation collections to suspend concurrent"        \
606           " marking in the old generation.")                                \
607                                                                             \
608   product(uintx, ShenandoahAgingCyclePeriod, 1, EXPERIMENTAL,               \
609           "With generational mode, increment the age of objects and"        \
610           "regions each time this many young-gen GC cycles are completed.") \
611                                                                             \
612   notproduct(bool, ShenandoahEnableCardStats, false,                        \
613           "Enable statistics collection related to clean & dirty cards")    \
614                                                                             \
615   notproduct(int, ShenandoahCardStatsLogInterval, 50,                       \
616           "Log cumulative card stats every so many remembered set or "      \
617           "update refs scans")                                              \
618   // end of GC_SHENANDOAH_FLAGS
619 
620 #endif // SHARE_GC_SHENANDOAH_SHENANDOAH_GLOBALS_HPP
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