1 /*
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  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
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 18  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 19  *
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 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                             range,                                          \
 34                             constraint)                                     \
 35                                                                             \
















































































 36   product(size_t, ShenandoahRegionSize, 0, EXPERIMENTAL,                    \
 37           "Static heap region size. Set zero to enable automatic sizing.")  \
 38                                                                             \
 39   product(size_t, ShenandoahTargetNumRegions, 2048, EXPERIMENTAL,           \
 40           "With automatic region sizing, this is the approximate number "   \
 41           "of regions that would be used, within min/max region size "      \
 42           "limits.")                                                        \
 43                                                                             \
 44   product(size_t, ShenandoahMinRegionSize, 256 * K, EXPERIMENTAL,           \
 45           "With automatic region sizing, the regions would be at least "    \
 46           "this large.")                                                    \
 47                                                                             \
 48   product(size_t, ShenandoahMaxRegionSize, 32 * M, EXPERIMENTAL,            \
 49           "With automatic region sizing, the regions would be at most "     \
 50           "this large.")                                                    \
 51                                                                             \
 52   product(ccstr, ShenandoahGCMode, "satb",                                  \
 53           "GC mode to use.  Among other things, this defines which "        \
 54           "barriers are in in use. Possible values are:"                    \
 55           " satb - snapshot-at-the-beginning concurrent GC (three pass mark-evac-update);"  \
 56           " iu - incremental-update concurrent GC (three pass mark-evac-update);"  \
 57           " passive - stop the world GC only (either degenerated or full)") \

 58                                                                             \
 59   product(ccstr, ShenandoahGCHeuristics, "adaptive",                        \
 60           "GC heuristics to use. This fine-tunes the GC mode selected, "    \
 61           "by choosing when to start the GC, how much to process on each "  \
 62           "cycle, and what other features to automatically enable. "        \
 63           "Possible values are:"                                            \
 64           " adaptive - adapt to maintain the given amount of free heap "    \
 65           "at all times, even during the GC cycle;"                         \
 66           " static -  trigger GC when free heap falls below the threshold;" \
 67           " aggressive - run GC continuously, try to evacuate everything;"  \
 68           " compact - run GC more frequently and with deeper targets to "   \
 69           "free up more memory.")                                           \
 70                                                                             \










 71   product(uintx, ShenandoahGarbageThreshold, 25, EXPERIMENTAL,              \
 72           "How much garbage a region has to contain before it would be "    \
 73           "taken for collection. This a guideline only, as GC heuristics "  \
 74           "may select the region for collection even if it has little "     \
 75           "garbage. This also affects how much internal fragmentation the " \
 76           "collector accepts. In percents of heap region size.")            \
 77           range(0,100)                                                      \
 78                                                                             \














 79   product(uintx, ShenandoahInitFreeThreshold, 70, EXPERIMENTAL,             \
 80           "How much heap should be free before some heuristics trigger the "\
 81           "initial (learning) cycles. Affects cycle frequency on startup "  \
 82           "and after drastic state changes, e.g. after degenerated/full "   \
 83           "GC cycles. In percents of (soft) max heap size.")                \


 84           range(0,100)                                                      \
 85                                                                             \
 86   product(uintx, ShenandoahMinFreeThreshold, 10, EXPERIMENTAL,              \
 87           "How much heap should be free before most heuristics trigger the "\
 88           "collection, even without other triggers. Provides the safety "   \
 89           "margin for many heuristics. In percents of (soft) max heap size.")\


 90           range(0,100)                                                      \
 91                                                                             \
 92   product(uintx, ShenandoahAllocationThreshold, 0, EXPERIMENTAL,            \
 93           "How many new allocations should happen since the last GC cycle " \
 94           "before some heuristics trigger the collection. In percents of "  \
 95           "(soft) max heap size. Set to zero to effectively disable.")      \
 96           range(0,100)                                                      \
 97                                                                             \
 98   product(uintx, ShenandoahAllocSpikeFactor, 5, EXPERIMENTAL,               \
 99           "How much of heap should some heuristics reserve for absorbing "  \
100           "the allocation spikes. Larger value wastes more memory in "      \
101           "non-emergency cases, but provides more safety in emergency "     \
102           "cases. In percents of (soft) max heap size.")                    \
103           range(0,100)                                                      \
104                                                                             \
105   product(uintx, ShenandoahLearningSteps, 5, EXPERIMENTAL,                  \
106           "The number of cycles some heuristics take to collect in order "  \
107           "to learn application and GC performance.")                       \
108           range(0,100)                                                      \
109                                                                             \
110   product(uintx, ShenandoahImmediateThreshold, 70, EXPERIMENTAL,            \
111           "The cycle may shortcut when enough garbage can be reclaimed "    \
112           "from the immediate garbage (completely garbage regions). "       \
113           "In percents of total garbage found. Setting this threshold "     \
114           "to 100 effectively disables the shortcut.")                      \
115           range(0,100)                                                      \
116                                                                             \
117   product(uintx, ShenandoahAdaptiveSampleFrequencyHz, 10, EXPERIMENTAL,     \
118           "The number of times per second to update the allocation rate "   \
119           "moving average.")                                                \
120                                                                             \
121   product(uintx, ShenandoahAdaptiveSampleSizeSeconds, 10, EXPERIMENTAL,     \
122           "The size of the moving window over which the average "           \
123           "allocation rate is maintained. The total number of samples "     \
124           "is the product of this number and the sample frequency.")        \
125                                                                             \
126   product(double, ShenandoahAdaptiveInitialConfidence, 1.8, EXPERIMENTAL,   \
127           "The number of standard deviations used to determine an initial " \
128           "margin of error for the average cycle time and average "         \
129           "allocation rate. Increasing this value will cause the "          \
130           "heuristic to initiate more concurrent cycles." )                 \
131                                                                             \
132   product(double, ShenandoahAdaptiveInitialSpikeThreshold, 1.8, EXPERIMENTAL, \
133           "If the most recently sampled allocation rate is more than "      \
134           "this many standard deviations away from the moving average, "    \
135           "then a cycle is initiated. This value controls how sensitive "   \
136           "the heuristic is to allocation spikes. Decreasing this number "  \
137           "increases the sensitivity. ")                                    \
138                                                                             \
139   product(double, ShenandoahAdaptiveDecayFactor, 0.5, EXPERIMENTAL,         \
140           "The decay factor (alpha) used for values in the weighted "       \
141           "moving average of cycle time and allocation rate. "              \
142           "Larger values give more weight to recent values.")               \
143           range(0,1.0)                                                      \
144                                                                             \
145   product(uintx, ShenandoahGuaranteedGCInterval, 5*60*1000, EXPERIMENTAL,   \
146           "Many heuristics would guarantee a concurrent GC cycle at "       \
147           "least with this interval. This is useful when large idle "       \
148           "intervals are present, where GC can run without stealing "       \
149           "time from active application. Time is in milliseconds. "         \
150           "Setting this to 0 disables the feature.")                        \
151                                                                             \










152   product(bool, ShenandoahAlwaysClearSoftRefs, false, EXPERIMENTAL,         \
153           "Unconditionally clear soft references, instead of using any "    \
154           "other cleanup policy. This minimizes footprint at expense of"    \
155           "more soft reference churn in applications.")                     \
156                                                                             \
157   product(bool, ShenandoahUncommit, true, EXPERIMENTAL,                     \
158           "Allow to uncommit memory under unused regions and metadata. "    \
159           "This optimizes footprint at expense of allocation latency in "   \
160           "regions that require committing back. Uncommits would be "       \
161           "disabled by some heuristics, or with static heap size.")         \
162                                                                             \
163   product(uintx, ShenandoahUncommitDelay, 5*60*1000, EXPERIMENTAL,          \
164           "Uncommit memory for regions that were not used for more than "   \
165           "this time. First use after that would incur allocation stalls. " \
166           "Actively used regions would never be uncommitted, because they " \
167           "do not become unused longer than this delay. Time is in "        \
168           "milliseconds. Setting this delay to 0 effectively uncommits "    \
169           "regions almost immediately after they become unused.")           \
170                                                                             \
171   product(bool, ShenandoahRegionSampling, false, EXPERIMENTAL,              \
172           "Provide heap region sampling data via jvmstat.")                 \
173                                                                             \
174   product(int, ShenandoahRegionSamplingRate, 40, EXPERIMENTAL,              \
175           "Sampling rate for heap region sampling. In milliseconds between "\
176           "the samples. Higher values provide more fidelity, at expense "   \
177           "of more sampling overhead.")                                     \
178                                                                             \
179   product(uintx, ShenandoahControlIntervalMin, 1, EXPERIMENTAL,             \
180           "The minimum sleep interval for the control loop that drives "    \
181           "the cycles. Lower values would increase GC responsiveness "      \
182           "to changing heap conditions, at the expense of higher perf "     \
183           "overhead. Time is in milliseconds.")                             \
184                                                                             \
185   product(uintx, ShenandoahControlIntervalMax, 10, EXPERIMENTAL,            \
186           "The maximum sleep interval for control loop that drives "        \
187           "the cycles. Lower values would increase GC responsiveness "      \
188           "to changing heap conditions, at the expense of higher perf "     \
189           "overhead. Time is in milliseconds.")                             \
190                                                                             \
191   product(uintx, ShenandoahControlIntervalAdjustPeriod, 1000, EXPERIMENTAL, \
192           "The time period for one step in control loop interval "          \
193           "adjustment. Lower values make adjustments faster, at the "       \
194           "expense of higher perf overhead. Time is in milliseconds.")      \
195                                                                             \
196   product(bool, ShenandoahVerify, false, DIAGNOSTIC,                        \
197           "Enable internal verification. This would catch many GC bugs, "   \
198           "but it would also stall the collector during the verification, " \
199           "which prolongs the pauses and might hide other bugs.")           \
200                                                                             \
201   product(intx, ShenandoahVerifyLevel, 4, DIAGNOSTIC,                       \
202           "Verification level, higher levels check more, taking more time. "\
203           "Accepted values are:"                                            \
204           " 0 = basic heap checks; "                                        \
205           " 1 = previous level, plus basic region checks; "                 \
206           " 2 = previous level, plus all roots; "                           \
207           " 3 = previous level, plus all reachable objects; "               \
208           " 4 = previous level, plus all marked objects")                   \
209                                                                             \
210   product(uintx, ShenandoahEvacReserve, 5, EXPERIMENTAL,                    \
211           "How much of heap to reserve for evacuations. Larger values make "\
212           "GC evacuate more live objects on every cycle, while leaving "    \
213           "less headroom for application to allocate in. In percents of "   \
214           "total heap size.")                                               \








215           range(1,100)                                                      \
216                                                                             \
217   product(double, ShenandoahEvacWaste, 1.2, EXPERIMENTAL,                   \
218           "How much waste evacuations produce within the reserved space. "  \
219           "Larger values make evacuations more resilient against "          \
220           "evacuation conflicts, at expense of evacuating less on each "    \
221           "GC cycle.")                                                      \

















222           range(1.0,100.0)                                                  \
223                                                                             \
224   product(bool, ShenandoahEvacReserveOverflow, true, EXPERIMENTAL,          \
225           "Allow evacuations to overflow the reserved space. Enabling it "  \
226           "will make evacuations more resilient when evacuation "           \
227           "reserve/waste is incorrect, at the risk that application "       \
228           "runs out of memory too early.")                                  \
229                                                                             \



































230   product(bool, ShenandoahPacing, true, EXPERIMENTAL,                       \
231           "Pace application allocations to give GC chance to start "        \
232           "and complete before allocation failure is reached.")             \
233                                                                             \
234   product(uintx, ShenandoahPacingMaxDelay, 10, EXPERIMENTAL,                \
235           "Max delay for pacing application allocations. Larger values "    \
236           "provide more resilience against out of memory, at expense at "   \
237           "hiding the GC latencies in the allocation path. Time is in "     \
238           "milliseconds. Setting it to arbitrarily large value makes "      \
239           "GC effectively stall the threads indefinitely instead of going " \
240           "to degenerated or Full GC.")                                     \
241                                                                             \
242   product(uintx, ShenandoahPacingIdleSlack, 2, EXPERIMENTAL,                \
243           "How much of heap counted as non-taxable allocations during idle "\
244           "phases. Larger value makes the pacing milder when collector is " \
245           "idle, requiring less rendezvous with control thread. Lower "     \
246           "value makes the pacing control less responsive to out-of-cycle " \
247           "allocs. In percent of total heap size.")                         \
248           range(0, 100)                                                     \
249                                                                             \
250   product(uintx, ShenandoahPacingCycleSlack, 10, EXPERIMENTAL,              \
251           "How much of free space to take as non-taxable allocations "      \
252           "the GC cycle. Larger value makes the pacing milder at the "      \
253           "beginning of the GC cycle. Lower value makes the pacing less "   \
254           "uniform during the cycle. In percent of free space.")            \
255           range(0, 100)                                                     \
256                                                                             \
257   product(double, ShenandoahPacingSurcharge, 1.1, EXPERIMENTAL,             \
258           "Additional pacing tax surcharge to help unclutter the heap. "    \
259           "Larger values makes the pacing more aggressive. Lower values "   \
260           "risk GC cycles finish with less memory than were available at "  \
261           "the beginning of it.")                                           \
262           range(1.0, 100.0)                                                 \
263                                                                             \
264   product(uintx, ShenandoahCriticalFreeThreshold, 1, EXPERIMENTAL,          \
265           "How much of the heap needs to be free after recovery cycles, "   \
266           "either Degenerated or Full GC to be claimed successful. If this "\
267           "much space is not available, next recovery step would be "       \
268           "triggered.")                                                     \
269           range(0, 100)                                                     \
270                                                                             \
271   product(bool, ShenandoahDegeneratedGC, true, DIAGNOSTIC,                  \
272           "Enable Degenerated GC as the graceful degradation step. "        \
273           "Disabling this option leads to degradation to Full GC instead. " \
274           "When running in passive mode, this can be toggled to measure "   \
275           "either Degenerated GC or Full GC costs.")                        \
276                                                                             \
277   product(uintx, ShenandoahFullGCThreshold, 3, EXPERIMENTAL,                \
278           "How many back-to-back Degenerated GCs should happen before "     \
279           "going to a Full GC.")                                            \
280                                                                             \
281   product(uintx, ShenandoahNoProgressThreshold, 5, EXPERIMENTAL,            \
282           "After this number of consecutive Full GCs fail to make "         \
283           "progress, Shenandoah will raise out of memory errors. Note "     \
284           "that progress is determined by ShenandoahCriticalFreeThreshold") \
285                                                                             \
286   product(bool, ShenandoahImplicitGCInvokesConcurrent, false, EXPERIMENTAL, \
287           "Should internally-caused GC requests invoke concurrent cycles, " \
288           "should they do the stop-the-world (Degenerated / Full GC)? "     \
289           "Many heuristics automatically enable this. This option is "      \
290           "similar to global ExplicitGCInvokesConcurrent.")                 \
291                                                                             \
292   product(bool, ShenandoahHumongousMoves, true, DIAGNOSTIC,                 \
293           "Allow moving humongous regions. This makes GC more resistant "   \
294           "to external fragmentation that may otherwise fail other "        \
295           "humongous allocations, at the expense of higher GC copying "     \
296           "costs. Currently affects stop-the-world (Full) cycle only.")     \
297                                                                             \
298   product(bool, ShenandoahOOMDuringEvacALot, false, DIAGNOSTIC,             \
299           "Testing: simulate OOM during evacuation.")                       \
300                                                                             \
301   product(bool, ShenandoahAllocFailureALot, false, DIAGNOSTIC,              \
302           "Testing: make lots of artificial allocation failures.")          \
303                                                                             \









304   product(intx, ShenandoahMarkScanPrefetch, 32, EXPERIMENTAL,               \
305           "How many objects to prefetch ahead when traversing mark bitmaps."\
306           "Set to 0 to disable prefetching.")                               \
307           range(0, 256)                                                     \
308                                                                             \
309   product(uintx, ShenandoahMarkLoopStride, 1000, EXPERIMENTAL,              \
310           "How many items to process during one marking iteration before "  \
311           "checking for cancellation, yielding, etc. Larger values improve "\
312           "marking performance at expense of responsiveness.")              \
313                                                                             \
314   product(uintx, ShenandoahParallelRegionStride, 0, EXPERIMENTAL,           \
315           "How many regions to process at once during parallel region "     \
316           "iteration. Affects heaps with lots of regions. "                 \
317           "Set to 0 to let Shenandoah to decide the best value.")           \
318                                                                             \
319   product(size_t, ShenandoahSATBBufferSize, 1 * K, EXPERIMENTAL,            \
320           "Number of entries in an SATB log buffer.")                       \
321           range(1, max_uintx)                                               \
322                                                                             \
323   product(uintx, ShenandoahMaxSATBBufferFlushes, 5, EXPERIMENTAL,           \
324           "How many times to maximum attempt to flush SATB buffers at the " \
325           "end of concurrent marking.")                                     \
326                                                                             \
327   product(bool, ShenandoahSATBBarrier, true, DIAGNOSTIC,                    \
328           "Turn on/off SATB barriers in Shenandoah")                        \
329                                                                             \




330   product(bool, ShenandoahCASBarrier, true, DIAGNOSTIC,                     \
331           "Turn on/off CAS barriers in Shenandoah")                         \
332                                                                             \
333   product(bool, ShenandoahCloneBarrier, true, DIAGNOSTIC,                   \
334           "Turn on/off clone barriers in Shenandoah")                       \
335                                                                             \
336   product(bool, ShenandoahLoadRefBarrier, true, DIAGNOSTIC,                 \
337           "Turn on/off load-reference barriers in Shenandoah")              \
338                                                                             \
339   product(bool, ShenandoahStackWatermarkBarrier, true, DIAGNOSTIC,          \
340           "Turn on/off stack watermark barriers in Shenandoah")             \
341                                                                             \
342   develop(bool, ShenandoahVerifyOptoBarriers, trueInDebug,                  \
343           "Verify no missing barriers in C2.")                              \
344                                                                             \
345 
346 // end of GC_SHENANDOAH_FLAGS



























347 
348 #endif // SHARE_GC_SHENANDOAH_SHENANDOAH_GLOBALS_HPP
--- EOF ---