1 /*
2 * Copyright (c) 2020, 2024, 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
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9 *
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14 * accompanied this code).
15 *
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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 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