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
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14 * accompanied this code).
15 *
16 * You should have received a copy of the GNU General Public License version
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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 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 " generational - generational concurrent GC") \
67 \
68 product(ccstr, ShenandoahGCHeuristics, "adaptive", \
69 "GC heuristics to use. This fine-tunes the GC mode selected, " \
70 "by choosing when to start the GC, how much to process on each " \
71 "cycle, and what other features to automatically enable. " \
72 "Possible values are:" \
73 " adaptive - adapt to maintain the given amount of free heap " \
74 "at all times, even during the GC cycle;" \
75 " static - trigger GC when free heap falls below the threshold;" \
76 " aggressive - run GC continuously, try to evacuate everything;" \
77 " compact - run GC more frequently and with deeper targets to " \
78 "free up more memory.") \
79 \
80 product(ccstr, ShenandoahOldGCHeuristics, "adaptive", \
81 "Similar to ShenandoahGCHeuristics, but applied to the old " \
82 "generation. This configuration is only used to trigger old " \
83 "collections and does not change how regions are selected " \
84 "for collection.") \
85 \
86 product(uintx, ShenandoahUnloadClassesFrequency, 1, EXPERIMENTAL, \
87 "Unload the classes every Nth cycle. Normally affects concurrent "\
88 "GC cycles, as degenerated and full GCs would try to unload " \
89 "classes regardless. Set to zero to disable class unloading.") \
90 \
91 product(uintx, ShenandoahGarbageThreshold, 25, EXPERIMENTAL, \
92 "How much garbage a region has to contain before it would be " \
93 "taken for collection. This a guideline only, as GC heuristics " \
94 "may select the region for collection even if it has little " \
95 "garbage. This also affects how much internal fragmentation the " \
96 "collector accepts. In percents of heap region size.") \
97 range(0,100) \
98 \
99 product(uintx, ShenandoahOldGarbageThreshold, 25, EXPERIMENTAL, \
100 "How much garbage an old region has to contain before it would " \
101 "be taken for collection.") \
102 range(0,100) \
103 \
104 product(uintx, ShenandoahInitFreeThreshold, 70, EXPERIMENTAL, \
105 "How much heap should be free before some heuristics trigger the "\
106 "initial (learning) cycles. Affects cycle frequency on startup " \
107 "and after drastic state changes, e.g. after degenerated/full " \
108 "GC cycles. In percents of (soft) max heap size.") \
109 range(0,100) \
110 \
111 product(uintx, ShenandoahMinFreeThreshold, 10, EXPERIMENTAL, \
112 "Percentage of free heap memory below which most heuristics " \
113 "trigger collection independent of other triggers. Provides " \
114 "a safety margin for many heuristics. In percents of (soft) " \
115 "max heap size.") \
116 range(0,100) \
117 \
118 product(uintx, ShenandoahAllocationThreshold, 0, EXPERIMENTAL, \
119 "How many new allocations should happen since the last GC cycle " \
120 "before some heuristics trigger the collection. In percents of " \
121 "(soft) max heap size. Set to zero to effectively disable.") \
122 range(0,100) \
123 \
124 product(uintx, ShenandoahAllocSpikeFactor, 5, EXPERIMENTAL, \
125 "How much of heap should some heuristics reserve for absorbing " \
126 "the allocation spikes. Larger value wastes more memory in " \
127 "non-emergency cases, but provides more safety in emergency " \
128 "cases. In percents of (soft) max heap size.") \
129 range(0,100) \
130 \
131 product(uintx, ShenandoahLearningSteps, 5, EXPERIMENTAL, \
132 "The number of cycles some heuristics take to collect in order " \
133 "to learn application and GC performance.") \
134 range(0,100) \
135 \
136 product(uintx, ShenandoahImmediateThreshold, 90, EXPERIMENTAL, \
137 "The cycle may shortcut when enough garbage can be reclaimed " \
138 "from the immediate garbage (completely garbage regions). " \
139 "In percents of total garbage found. Setting this threshold " \
140 "to 100 effectively disables the shortcut.") \
141 range(0,100) \
142 \
143 product(uintx, ShenandoahAdaptiveSampleFrequencyHz, 10, EXPERIMENTAL, \
144 "The number of times per second to update the allocation rate " \
145 "moving average.") \
146 \
147 product(uintx, ShenandoahAdaptiveSampleSizeSeconds, 10, EXPERIMENTAL, \
148 "The size of the moving window over which the average " \
149 "allocation rate is maintained. The total number of samples " \
150 "is the product of this number and the sample frequency.") \
151 \
152 product(double, ShenandoahAdaptiveInitialConfidence, 1.8, EXPERIMENTAL, \
153 "The number of standard deviations used to determine an initial " \
154 "margin of error for the average cycle time and average " \
155 "allocation rate. Increasing this value will cause the " \
156 "heuristic to initiate more concurrent cycles." ) \
157 \
158 product(double, ShenandoahAdaptiveInitialSpikeThreshold, 1.8, EXPERIMENTAL, \
159 "If the most recently sampled allocation rate is more than " \
160 "this many standard deviations away from the moving average, " \
161 "then a cycle is initiated. This value controls how sensitive " \
162 "the heuristic is to allocation spikes. Decreasing this number " \
163 "increases the sensitivity. ") \
164 \
165 product(double, ShenandoahAdaptiveDecayFactor, 0.5, EXPERIMENTAL, \
166 "The decay factor (alpha) used for values in the weighted " \
167 "moving average of cycle time and allocation rate. " \
168 "Larger values give more weight to recent values.") \
169 range(0,1.0) \
170 \
171 product(uintx, ShenandoahGuaranteedGCInterval, 5*60*1000, EXPERIMENTAL, \
172 "Many heuristics would guarantee a concurrent GC cycle at " \
173 "least with this interval. This is useful when large idle " \
174 "intervals are present, where GC can run without stealing " \
175 "time from active application. Time is in milliseconds. " \
176 "Setting this to 0 disables the feature.") \
177 \
178 product(uintx, ShenandoahGuaranteedOldGCInterval, 10*60*1000, EXPERIMENTAL, \
179 "Run a collection of the old generation at least this often. " \
180 "Heuristics may trigger collections more frequently. Time is in " \
181 "milliseconds. Setting this to 0 disables the feature.") \
182 \
183 product(bool, ShenandoahAlwaysClearSoftRefs, false, EXPERIMENTAL, \
184 "Unconditionally clear soft references, instead of using any " \
185 "other cleanup policy. This minimizes footprint at expense of" \
186 "more soft reference churn in applications.") \
187 \
188 product(bool, ShenandoahUncommit, true, EXPERIMENTAL, \
189 "Allow to uncommit memory under unused regions and metadata. " \
190 "This optimizes footprint at expense of allocation latency in " \
191 "regions that require committing back. Uncommits would be " \
192 "disabled by some heuristics, or with static heap size.") \
193 \
194 product(uintx, ShenandoahUncommitDelay, 5*60*1000, EXPERIMENTAL, \
195 "Uncommit memory for regions that were not used for more than " \
196 "this time. First use after that would incur allocation stalls. " \
197 "Actively used regions would never be uncommitted, because they " \
198 "do not become unused longer than this delay. Time is in " \
199 "milliseconds. Setting this delay to 0 effectively uncommits " \
200 "regions almost immediately after they become unused.") \
201 \
202 product(bool, ShenandoahRegionSampling, false, EXPERIMENTAL, \
203 "Provide heap region sampling data via jvmstat.") \
204 \
205 product(int, ShenandoahRegionSamplingRate, 40, EXPERIMENTAL, \
206 "Sampling rate for heap region sampling. In milliseconds between "\
207 "the samples. Higher values provide more fidelity, at expense " \
208 "of more sampling overhead.") \
209 \
210 product(bool, ShenandoahLogRegionSampling, false, \
211 "Save region sampling stream to ShenandoahRegionSamplingFile") \
212 \
213 product(ccstr, ShenandoahRegionSamplingFile, \
214 "./shenandoahSnapshots_pid%p.log", \
215 "If ShenandoahLogRegionSampling is on, save sampling data stream "\
216 "to this file [default: ./shenandoahSnapshots_pid%p.log] " \
217 "(%p replaced with pid)") \
218 \
219 product(uintx, ShenandoahControlIntervalMin, 1, EXPERIMENTAL, \
220 "The minimum sleep interval for the control loop that drives " \
221 "the cycles. Lower values would increase GC responsiveness " \
222 "to changing heap conditions, at the expense of higher perf " \
223 "overhead. Time is in milliseconds.") \
224 \
225 product(uintx, ShenandoahControlIntervalMax, 10, EXPERIMENTAL, \
226 "The maximum sleep interval for control loop that drives " \
227 "the cycles. Lower values would increase GC responsiveness " \
228 "to changing heap conditions, at the expense of higher perf " \
229 "overhead. Time is in milliseconds.") \
230 \
231 product(uintx, ShenandoahControlIntervalAdjustPeriod, 1000, EXPERIMENTAL, \
232 "The time period for one step in control loop interval " \
233 "adjustment. Lower values make adjustments faster, at the " \
234 "expense of higher perf overhead. Time is in milliseconds.") \
235 \
236 product(bool, ShenandoahVerify, false, DIAGNOSTIC, \
237 "Enable internal verification. This would catch many GC bugs, " \
238 "but it would also stall the collector during the verification, " \
239 "which prolongs the pauses and might hide other bugs.") \
240 \
241 product(intx, ShenandoahVerifyLevel, 4, DIAGNOSTIC, \
242 "Verification level, higher levels check more, taking more time. "\
243 "Accepted values are:" \
244 " 0 = basic heap checks; " \
245 " 1 = previous level, plus basic region checks; " \
246 " 2 = previous level, plus all roots; " \
247 " 3 = previous level, plus all reachable objects; " \
248 " 4 = previous level, plus all marked objects") \
249 \
250 product(bool, ShenandoahElasticTLAB, true, DIAGNOSTIC, \
251 "Use Elastic TLABs with Shenandoah") \
252 \
253 product(bool, ShenandoahUsePLAB, true, DIAGNOSTIC, \
254 "Use PLABs for object promotions with Shenandoah, " \
255 "if in generational mode and UseTLAB is also set.") \
256 \
257 product(uintx, ShenandoahEvacReserve, 5, EXPERIMENTAL, \
258 "How much of heap to reserve for evacuations. Larger values make "\
259 "GC evacuate more live objects on every cycle, while leaving " \
260 "less headroom for application to allocate in. In percents of " \
261 "total heap size.") \
262 range(1,100) \
263 \
264 product(double, ShenandoahEvacWaste, 1.2, EXPERIMENTAL, \
265 "How much waste evacuations produce within the reserved space. " \
266 "Larger values make evacuations more resilient against " \
267 "evacuation conflicts, at expense of evacuating less on each " \
268 "GC cycle.") \
269 range(1.0,100.0) \
270 \
271 product(bool, ShenandoahEvacReserveOverflow, true, EXPERIMENTAL, \
272 "Allow evacuations to overflow the reserved space. Enabling it " \
273 "will make evacuations more resilient when evacuation " \
274 "reserve/waste is incorrect, at the risk that application " \
275 "runs out of memory too early.") \
276 \
277 product(double, ShenandoahOldEvacReserve, 5.0, EXPERIMENTAL, \
278 "How much of old generation to withhold from evacuations. " \
279 "Larger values will result in fewer live objects being " \
280 "evacuated in the old generation.") \
281 range(1,100) \
282 \
283 product(bool, ShenandoahPacing, true, EXPERIMENTAL, \
284 "Pace application allocations to give GC chance to start " \
285 "and complete before allocation failure is reached.") \
286 \
287 product(uintx, ShenandoahPacingMaxDelay, 10, EXPERIMENTAL, \
288 "Max delay for pacing application allocations. Larger values " \
289 "provide more resilience against out of memory, at expense at " \
290 "hiding the GC latencies in the allocation path. Time is in " \
291 "milliseconds. Setting it to arbitrarily large value makes " \
292 "GC effectively stall the threads indefinitely instead of going " \
293 "to degenerated or Full GC.") \
294 \
295 product(uintx, ShenandoahPacingIdleSlack, 2, EXPERIMENTAL, \
296 "How much of heap counted as non-taxable allocations during idle "\
297 "phases. Larger value makes the pacing milder when collector is " \
298 "idle, requiring less rendezvous with control thread. Lower " \
299 "value makes the pacing control less responsive to out-of-cycle " \
300 "allocs. In percent of total heap size.") \
301 range(0, 100) \
302 \
303 product(uintx, ShenandoahPacingCycleSlack, 10, EXPERIMENTAL, \
304 "How much of free space to take as non-taxable allocations " \
305 "the GC cycle. Larger value makes the pacing milder at the " \
306 "beginning of the GC cycle. Lower value makes the pacing less " \
307 "uniform during the cycle. In percent of free space.") \
308 range(0, 100) \
309 \
310 product(double, ShenandoahPacingSurcharge, 1.1, EXPERIMENTAL, \
311 "Additional pacing tax surcharge to help unclutter the heap. " \
312 "Larger values makes the pacing more aggressive. Lower values " \
313 "risk GC cycles finish with less memory than were available at " \
314 "the beginning of it.") \
315 range(1.0, 100.0) \
316 \
317 product(uintx, ShenandoahCriticalFreeThreshold, 1, EXPERIMENTAL, \
318 "How much of the heap needs to be free after recovery cycles, " \
319 "either Degenerated or Full GC to be claimed successful. If this "\
320 "much space is not available, next recovery step would be " \
321 "triggered.") \
322 range(0, 100) \
323 \
324 product(bool, ShenandoahDegeneratedGC, true, DIAGNOSTIC, \
325 "Enable Degenerated GC as the graceful degradation step. " \
326 "Disabling this option leads to degradation to Full GC instead. " \
327 "When running in passive mode, this can be toggled to measure " \
328 "either Degenerated GC or Full GC costs.") \
329 \
330 product(uintx, ShenandoahFullGCThreshold, 3, EXPERIMENTAL, \
331 "How many back-to-back Degenerated GCs should happen before " \
332 "going to a Full GC.") \
333 \
334 product(bool, ShenandoahImplicitGCInvokesConcurrent, false, EXPERIMENTAL, \
335 "Should internally-caused GC requests invoke concurrent cycles, " \
336 "should they do the stop-the-world (Degenerated / Full GC)? " \
337 "Many heuristics automatically enable this. This option is " \
338 "similar to global ExplicitGCInvokesConcurrent.") \
339 \
340 product(bool, ShenandoahHumongousMoves, true, DIAGNOSTIC, \
341 "Allow moving humongous regions. This makes GC more resistant " \
342 "to external fragmentation that may otherwise fail other " \
343 "humongous allocations, at the expense of higher GC copying " \
344 "costs. Currently affects stop-the-world (Full) cycle only.") \
345 \
346 product(bool, ShenandoahOOMDuringEvacALot, false, DIAGNOSTIC, \
347 "Testing: simulate OOM during evacuation.") \
348 \
349 product(bool, ShenandoahAllocFailureALot, false, DIAGNOSTIC, \
350 "Testing: make lots of artificial allocation failures.") \
351 \
352 product(intx, ShenandoahMarkScanPrefetch, 32, EXPERIMENTAL, \
353 "How many objects to prefetch ahead when traversing mark bitmaps."\
354 "Set to 0 to disable prefetching.") \
355 range(0, 256) \
356 \
357 product(uintx, ShenandoahMarkLoopStride, 1000, EXPERIMENTAL, \
358 "How many items to process during one marking iteration before " \
359 "checking for cancellation, yielding, etc. Larger values improve "\
360 "marking performance at expense of responsiveness.") \
361 \
362 product(uintx, ShenandoahParallelRegionStride, 1024, EXPERIMENTAL, \
363 "How many regions to process at once during parallel region " \
364 "iteration. Affects heaps with lots of regions.") \
365 \
366 product(size_t, ShenandoahSATBBufferSize, 1 * K, EXPERIMENTAL, \
367 "Number of entries in an SATB log buffer.") \
368 range(1, max_uintx) \
369 \
370 product(uintx, ShenandoahMaxSATBBufferFlushes, 5, EXPERIMENTAL, \
371 "How many times to maximum attempt to flush SATB buffers at the " \
372 "end of concurrent marking.") \
373 \
374 product(bool, ShenandoahSuspendibleWorkers, false, EXPERIMENTAL, \
375 "Suspend concurrent GC worker threads at safepoints") \
376 \
377 product(bool, ShenandoahSATBBarrier, true, DIAGNOSTIC, \
378 "Turn on/off SATB barriers in Shenandoah") \
379 \
380 product(bool, ShenandoahIUBarrier, false, DIAGNOSTIC, \
381 "Turn on/off I-U barriers barriers in Shenandoah") \
382 \
383 product(bool, ShenandoahCASBarrier, true, DIAGNOSTIC, \
384 "Turn on/off CAS barriers in Shenandoah") \
385 \
386 product(bool, ShenandoahCloneBarrier, true, DIAGNOSTIC, \
387 "Turn on/off clone barriers in Shenandoah") \
388 \
389 product(bool, ShenandoahLoadRefBarrier, true, DIAGNOSTIC, \
390 "Turn on/off load-reference barriers in Shenandoah") \
391 \
392 product(bool, ShenandoahNMethodBarrier, true, DIAGNOSTIC, \
393 "Turn on/off NMethod entry barriers in Shenandoah") \
394 \
395 product(bool, ShenandoahStackWatermarkBarrier, true, DIAGNOSTIC, \
396 "Turn on/off stack watermark barriers in Shenandoah") \
397 \
398 develop(bool, ShenandoahVerifyOptoBarriers, false, \
399 "Verify no missing barriers in C2.") \
400 \
401 product(bool, ShenandoahLoopOptsAfterExpansion, true, DIAGNOSTIC, \
402 "Attempt more loop opts after barrier expansion.") \
403 \
404 product(bool, ShenandoahSelfFixing, true, DIAGNOSTIC, \
405 "Fix references with load reference barrier. Disabling this " \
406 "might degrade performance.") \
407 \
408 product(uintx, ShenandoahTenuredRegionUsageBias, 192, EXPERIMENTAL, \
409 "The collection set is comprised of heap regions that contain " \
410 "the greatest amount of garbage. " \
411 "For purposes of selecting regions to be included in the " \
412 "collection set, regions that have reached the tenure age will " \
413 "be treated as if their contained garbage is the actual " \
414 "contained garbage multiplied by " \
415 "(ShenandoahTenuredRegionUsageBias / 128 (e.g. 150% for the " \
416 "default value) as many times as the region's age meets or " \
417 "exceeds the tenure age. For example, if tenure age is 7, " \
418 "the region age is 9, ShenandoahTenuredRegionUsageBias is " \
419 "192, and the region is 12.5% garbage, this region " \
420 "will by treated as if its garbage content is " \
421 "1/8 * 27/8 = 42.2% when comparing this region to untenured " \
422 "regions.") \
423 range(128, 256) \
424 \
425 product(bool, ShenandoahPromoteTenuredObjects, true, DIAGNOSTIC, \
426 "Turn on/off evacuating individual tenured young objects " \
427 " to the old generation.") \
428 \
429 product(bool, ShenandoahAllowOldMarkingPreemption, true, DIAGNOSTIC, \
430 "Allow young generation collections to suspend concurrent" \
431 " marking in the old generation.") \
432 \
433 product(uintx, ShenandoahAgingCyclePeriod, 1, EXPERIMENTAL, \
434 "With generational mode, increment the age of objects and" \
435 "regions each time this many young-gen GC cycles are completed.")
436 // end of GC_SHENANDOAH_FLAGS
437
438 // 2^ShenandoahTenuredRegionUsageBiasLogBase2 is 128
439 #define ShenandoahTenuredRegionUsageBiasLogBase2 7
440
441 #endif // SHARE_GC_SHENANDOAH_SHENANDOAH_GLOBALS_HPP