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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 range, \
35 constraint) \
36 \
37 product(uint, ShenandoahAccelerationSamplePeriod, 15, EXPERIMENTAL, \
38 "When at least this much time (measured in ms) has passed " \
39 "since the acceleration allocation rate was most recently " \
40 "sampled, capture another allocation rate sample for the purpose "\
41 "of detecting acceleration or momentary spikes in allocation " \
42 "rate. A smaller value allows quicker response to changes in " \
43 "allocation rates but is more vulnerable to noise and requires " \
44 "more monitoring effort.") \
45 range(1, 1000) \
46 \
47 product(uint, ShenandoahRateAccelerationSampleSize, 8, EXPERIMENTAL, \
48 "In selected ShenandoahControlIntervals " \
49 "(if ShenandoahAccelerationSamplePeriod ms have passed " \
50 "since previous allocation rate sample), " \
51 "we compute the allocation rate since the previous rate was " \
52 "sampled. This many samples are analyzed to determine whether " \
53 "allocation rates are accelerating. Acceleration may occur " \
54 "due to increasing client demand or due to phase changes in " \
55 "an application. A larger value reduces sensitivity to " \
56 "noise and delays recognition of the accelerating trend. A " \
57 "larger value may also cause the heuristic to miss detection " \
58 "of very quick accelerations. Smaller values may cause random " \
59 "noise to be perceived as acceleration of allocation rate, " \
60 "triggering excess collections. Note that the acceleration " \
61 "need not last the entire span of the sampled duration to be " \
62 "detected. If the last several of all samples are signficantly " \
63 "larger than the other samples, the best fit line through all " \
64 "sampled values will have an upward slope, manifesting as " \
65 "acceleration.") \
66 range(1,64) \
67 \
68 product(uint, ShenandoahMomentaryAllocationRateSpikeSampleSize, \
69 2, EXPERIMENTAL, \
70 "In selected ShenandoahControlIntervals " \
71 "(if ShenandoahAccelerationSamplePeriod ms have passed " \
72 "since previous allocation rate sample), we compute " \
73 "the allocation rate since the previous rate was sampled. " \
74 "The weighted average of this " \
75 "many most recent momentary allocation rate samples is compared " \
76 "against current allocation runway and anticipated GC time to " \
77 "determine whether a spike in momentary allocation rate " \
78 "justifies an early GC trigger. Momentary allocation spike " \
79 "detection is in addition to previously implemented " \
80 "ShenandoahAdaptiveInitialSpikeThreshold, the latter of which " \
81 "is more effective at detecting slower spikes. The latter " \
82 "spike detection samples at the rate specifieid by " \
83 "ShenandoahAdaptiveSampleFrequencyHz. The value of this " \
84 "parameter must be less than the value of " \
85 "ShenandoahRateAccelerationSampleSize. A larger value makes " \
86 "momentary spike detection less sensitive. A smaller value " \
87 "may result in excessive GC triggers.") \
88 range(1,64) \
89 \
90 product(uintx, ShenandoahGenerationalMinPIPUsage, 30, EXPERIMENTAL, \
91 "(Generational mode only) What percent of a heap region " \
92 "should be used before we consider promoting a region in " \
93 "place? Regions with less than this amount of used will " \
94 "promoted by evacuation. A benefit of promoting in place " \
95 "is that less work is required by the GC at the time the " \
96 "region is promoted. A disadvantage of promoting in place " \
97 "is that this introduces fragmentation of old-gen memory, " \
98 "with old-gen regions scattered throughout the heap. Regions " \
99 "that have been promoted in place may need to be evacuated at " \
100 "a later time in order to compact old-gen memory to enable " \
101 "future humongous allocations.") \
102 range(0,100) \
103 \
104 product(uintx, ShenandoahGenerationalHumongousReserve, 0, EXPERIMENTAL, \
105 "(Generational mode only) What percent of the heap should be " \
106 "reserved for humongous objects if possible. Old-generation " \
107 "collections will endeavor to evacuate old-gen regions within " \
108 "this reserved area even if these regions do not contain high " \
109 "percentage of garbage. Setting a larger value will cause " \
110 "more frequent old-gen collections. A smaller value will " \
111 "increase the likelihood that humongous object allocations " \
112 "fail, resulting in stop-the-world full GCs.") \
113 range(0,100) \
114 \
115 product(double, ShenandoahMinOldGenGrowthPercent, 50, EXPERIMENTAL, \
116 "(Generational mode only) If the usage within old generation " \
117 "has grown by at least this percent of its live memory size " \
118 "at the start of the previous old-generation marking effort, " \
119 "heuristics may trigger the start of a new old-gen collection.") \
120 range(0.0,100.0) \
121 \
122 product(double, ShenandoahMinOldGenGrowthRemainingHeapPercent, \
123 35, EXPERIMENTAL, \
124 "(Generational mode only) If the usage within old generation " \
125 "has grown to exceed this percent of the remaining heap that " \
126 "was not marked live within the old generation at the time " \
127 "of the last old-generation marking effort, heuristics may " \
128 "trigger the start of a new old-gen collection. Setting " \
129 "this value to a smaller value may cause back-to-back old " \
130 "generation marking triggers, since the typical memory used " \
131 "by the old generation is about 30% larger than the live " \
132 "memory contained within the old generation (because default " \
133 "value of ShenandoahOldGarbageThreshold is 25.") \
134 range(0.0,100.0) \
135 \
136 product(uintx, ShenandoahIgnoreOldGrowthBelowPercentage, \
137 40, EXPERIMENTAL, \
138 "(Generational mode only) If the total usage of the old " \
139 "generation is smaller than this percent, we do not trigger " \
140 "old gen collections even if old has grown, except when " \
141 "ShenandoahGenerationalDoNotIgnoreGrowthAfterYoungCycles " \
142 "consecutive cycles have been completed following the " \
143 "preceding old-gen collection.") \
144 range(0,100) \
145 \
146 product(uintx, ShenandoahDoNotIgnoreGrowthAfterYoungCycles, \
147 100, EXPERIMENTAL, \
148 "(Generational mode only) Trigger an old-generation mark " \
149 "if old has grown and this many consecutive young-gen " \
150 "collections have been completed following the preceding " \
151 "old-gen collection. We perform this old-generation mark " \
152 "evvort even if the usage of old generation is below " \
153 "ShenandoahIgnoreOldGrowthBelowPercentage.") \
154 \
155 product(bool, ShenandoahGenerationalCensusIgnoreOlderCohorts, true, \
156 EXPERIMENTAL,\
157 "(Generational mode only) Ignore mortality rates older than the " \
158 "oldest cohort under the tenuring age for the last cycle." ) \
159 \
160 product(uintx, ShenandoahGenerationalMinTenuringAge, 1, EXPERIMENTAL, \
161 "(Generational mode only) Floor for adaptive tenuring age. " \
162 "Setting floor and ceiling to the same value fixes the tenuring " \
163 "age; setting both to 1 simulates a poor approximation to " \
164 "AlwaysTenure, and setting both to 16 simulates NeverTenure.") \
165 range(1,16) \
166 \
167 product(uintx, ShenandoahGenerationalMaxTenuringAge, 15, EXPERIMENTAL, \
168 "(Generational mode only) Ceiling for adaptive tenuring age. " \
169 "Setting floor and ceiling to the same value fixes the tenuring " \
170 "age; setting both to 1 simulates a poor approximation to " \
171 "AlwaysTenure, and setting both to 16 simulates NeverTenure.") \
172 range(1,16) \
173 \
174 product(double, ShenandoahGenerationalTenuringMortalityRateThreshold, \
175 0.1, EXPERIMENTAL, \
176 "(Generational mode only) Cohort mortality rates below this " \
177 "value will be treated as indicative of longevity, leading to " \
178 "tenuring. A lower value delays tenuring, a higher value hastens "\
179 "it.") \
180 range(0.001,0.999) \
181 \
182 product(size_t, ShenandoahGenerationalTenuringCohortPopulationThreshold, \
183 4*K, EXPERIMENTAL, \
184 "(Generational mode only) Cohorts whose population is lower than "\
185 "this value in the previous census are ignored wrt tenuring " \
186 "decisions. Effectively this makes then tenurable as soon as all "\
187 "older cohorts are. Set this value to the largest cohort " \
188 "population volume that you are comfortable ignoring when making "\
189 "tenuring decisions.") \
190 \
191 product(size_t, ShenandoahRegionSize, 0, EXPERIMENTAL, \
192 "Static heap region size. Set zero to enable automatic sizing.") \
193 \
194 product(size_t, ShenandoahTargetNumRegions, 2048, EXPERIMENTAL, \
195 "With automatic region sizing, this is the approximate number " \
196 "of regions that would be used, within min/max region size " \
197 "limits.") \
198 \
199 product(size_t, ShenandoahMinRegionSize, 256 * K, EXPERIMENTAL, \
200 "With automatic region sizing, the regions would be at least " \
201 "this large.") \
202 \
203 product(size_t, ShenandoahMaxRegionSize, 32 * M, EXPERIMENTAL, \
204 "With automatic region sizing, the regions would be at most " \
205 "this large.") \
206 \
207 product(ccstr, ShenandoahGCMode, "satb", \
208 "GC mode to use. Among other things, this defines which " \
209 "barriers are in in use. Possible values are:" \
210 " satb - snapshot-at-the-beginning concurrent GC (three pass mark-evac-update);" \
211 " passive - stop the world GC only (either degenerated or full);" \
212 " generational - generational concurrent GC") \
213 \
214 product(ccstr, ShenandoahGCHeuristics, "adaptive", \
215 "GC heuristics to use. This fine-tunes the GC mode selected, " \
216 "by choosing when to start the GC, how much to process on each " \
217 "cycle, and what other features to automatically enable. " \
218 "When -XX:ShenandoahGCMode is generational, the only supported " \
219 "option is the default, adaptive. Possible values are:" \
220 " adaptive - adapt to maintain the given amount of free heap " \
221 "at all times, even during the GC cycle;" \
222 " static - trigger GC when free heap falls below a specified " \
223 "threshold;" \
224 " aggressive - run GC continuously, try to evacuate everything;" \
225 " compact - run GC more frequently and with deeper targets to " \
226 "free up more memory.") \
227 \
228 product(uintx, ShenandoahExpeditePromotionsThreshold, 5, EXPERIMENTAL, \
229 "When Shenandoah expects to promote at least this percentage " \
230 "of the young generation, trigger a young collection to " \
231 "expedite these promotions.") \
232 range(0,100) \
233 \
234 product(uintx, ShenandoahExpediteMixedThreshold, 10, EXPERIMENTAL, \
235 "When there are this many old regions waiting to be collected, " \
236 "trigger a mixed collection immediately.") \
237 \
238 product(uintx, ShenandoahGarbageThreshold, 25, EXPERIMENTAL, \
239 "How much garbage a region has to contain before it would be " \
240 "taken for collection. This a guideline only, as GC heuristics " \
241 "may select the region for collection even if it has little " \
242 "garbage. This also affects how much internal fragmentation the " \
243 "collector accepts. In percents of heap region size.") \
244 range(0,100) \
245 \
246 product(uintx, ShenandoahOldGarbageThreshold, 25, EXPERIMENTAL, \
247 "How much garbage an old region has to contain before it would " \
248 "be taken for collection.") \
249 range(0,100) \
250 \
251 product(uintx, ShenandoahIgnoreGarbageThreshold, 5, EXPERIMENTAL, \
252 "When less than this amount of garbage (as a percentage of " \
253 "region size) exists within a region, the region will not be " \
254 "added to the collection set, even when the heuristic has " \
255 "chosen to aggressively add regions with less than " \
256 "ShenandoahGarbageThreshold amount of garbage into the " \
257 "collection set.") \
258 range(0,100) \
259 \
260 product(uintx, ShenandoahInitFreeThreshold, 70, EXPERIMENTAL, \
261 "When less than this amount of memory is free within the " \
262 "heap or generation, trigger a learning cycle if we are " \
263 "in learning mode. Learning mode happens during initialization " \
264 "and following a drastic state change, such as following a " \
265 "degenerated or Full GC cycle. In percents of soft max " \
266 "heap size.") \
267 range(0,100) \
268 \
269 product(uintx, ShenandoahMinFreeThreshold, 10, EXPERIMENTAL, \
270 "Percentage of free heap memory (or young generation, in " \
271 "generational mode) below which most heuristics trigger " \
272 "collection independent of other triggers. Provides a safety " \
273 "margin for many heuristics. In percents of (soft) max heap " \
274 "size.") \
275 range(0,100) \
276 \
277 product(uintx, ShenandoahAllocationThreshold, 0, EXPERIMENTAL, \
278 "How many new allocations should happen since the last GC cycle " \
279 "before some heuristics trigger the collection. In percents of " \
280 "(soft) max heap size. Set to zero to effectively disable.") \
281 range(0,100) \
282 \
283 product(uintx, ShenandoahAllocSpikeFactor, 5, EXPERIMENTAL, \
284 "How much of heap should some heuristics reserve for absorbing " \
285 "the allocation spikes. Larger value wastes more memory in " \
286 "non-emergency cases, but provides more safety in emergency " \
287 "cases. In percents of (soft) max heap size.") \
288 range(0,100) \
289 \
290 product(uintx, ShenandoahLearningSteps, 5, EXPERIMENTAL, \
291 "The number of cycles some heuristics take to collect in order " \
292 "to learn application and GC performance.") \
293 range(0,100) \
294 \
295 product(uintx, ShenandoahImmediateThreshold, 70, EXPERIMENTAL, \
296 "The cycle may shortcut when enough garbage can be reclaimed " \
297 "from the immediate garbage (completely garbage regions). " \
298 "In percents of total garbage found. Setting this threshold " \
299 "to 100 effectively disables the shortcut.") \
300 range(0,100) \
301 \
302 product(uintx, ShenandoahAdaptiveSampleFrequencyHz, 10, EXPERIMENTAL, \
303 "The number of times per second to update the allocation rate " \
304 "moving average.") \
305 \
306 product(uintx, ShenandoahAdaptiveSampleSizeSeconds, 10, EXPERIMENTAL, \
307 "The size of the moving window over which the average " \
308 "allocation rate is maintained. The total number of samples " \
309 "is the product of this number and the sample frequency.") \
310 \
311 product(double, ShenandoahAdaptiveInitialConfidence, 1.8, EXPERIMENTAL, \
312 "The number of standard deviations used to determine an initial " \
313 "margin of error for the average cycle time and average " \
314 "allocation rate. Increasing this value will cause the " \
315 "heuristic to initiate more concurrent cycles." ) \
316 \
317 product(double, ShenandoahAdaptiveInitialSpikeThreshold, 1.8, EXPERIMENTAL, \
318 "If the most recently sampled allocation rate is more than " \
319 "this many standard deviations away from the moving average, " \
320 "then a cycle is initiated. This value controls how sensitive " \
321 "the heuristic is to allocation spikes. Decreasing this number " \
322 "increases the sensitivity. ") \
323 \
324 product(double, ShenandoahAdaptiveDecayFactor, 0.5, EXPERIMENTAL, \
325 "The decay factor (alpha) used for values in the weighted " \
326 "moving average of cycle time and allocation rate. " \
327 "Larger values give more weight to recent values.") \
328 range(0,1.0) \
329 \
330 product(uintx, ShenandoahGuaranteedGCInterval, 5*60*1000, EXPERIMENTAL, \
331 "Many heuristics would guarantee a concurrent GC cycle at " \
332 "least with this interval. This is useful when large idle " \
333 "intervals are present, where GC can run without stealing " \
334 "time from active application. Time is in milliseconds. " \
335 "Setting this to 0 disables the feature.") \
336 \
337 product(uintx, ShenandoahGuaranteedOldGCInterval, 10*60*1000, EXPERIMENTAL, \
338 "Run a collection of the old generation at least this often. " \
339 "Heuristics may trigger collections more frequently. Time is in " \
340 "milliseconds. Setting this to 0 disables the feature.") \
341 \
342 product(uintx, ShenandoahGuaranteedYoungGCInterval, 5*60*1000, EXPERIMENTAL, \
343 "Run a collection of the young generation at least this often. " \
344 "Heuristics may trigger collections more frequently. Time is in " \
345 "milliseconds. Setting this to 0 disables the feature.") \
346 \
347 product(bool, ShenandoahAlwaysClearSoftRefs, false, EXPERIMENTAL, \
348 "Unconditionally clear soft references, instead of using any " \
349 "other cleanup policy. This minimizes footprint at expense of" \
350 "more soft reference churn in applications.") \
351 \
352 product(bool, ShenandoahUncommit, true, EXPERIMENTAL, \
353 "Allow to uncommit memory under unused regions and metadata. " \
354 "This optimizes footprint at expense of allocation latency in " \
355 "regions that require committing back. Uncommits would be " \
356 "disabled by some heuristics, or with static heap size.") \
357 \
358 product(uintx, ShenandoahUncommitDelay, 5*60*1000, EXPERIMENTAL, \
359 "Uncommit memory for regions that were not used for more than " \
360 "this time. First use after that would incur allocation stalls. " \
361 "Actively used regions would never be uncommitted, because they " \
362 "do not become unused longer than this delay. Time is in " \
363 "milliseconds. Setting this delay to 0 effectively uncommits " \
364 "regions almost immediately after they become unused.") \
365 \
366 product(bool, ShenandoahRegionSampling, false, EXPERIMENTAL, \
367 "Provide heap region sampling data via jvmstat.") \
368 \
369 product(int, ShenandoahRegionSamplingRate, 40, EXPERIMENTAL, \
370 "Sampling rate for heap region sampling. In milliseconds between "\
371 "the samples. Higher values provide more fidelity, at expense " \
372 "of more sampling overhead.") \
373 \
374 product(uintx, ShenandoahControlIntervalMin, 1, EXPERIMENTAL, \
375 "The minimum sleep interval for the control loop that drives " \
376 "the cycles. Lower values would increase GC responsiveness " \
377 "to changing heap conditions, at the expense of higher perf " \
378 "overhead. Time is in milliseconds.") \
379 range(1, 999) \
380 \
381 product(uintx, ShenandoahControlIntervalMax, 10, EXPERIMENTAL, \
382 "The maximum sleep interval for control loop that drives " \
383 "the cycles. Lower values would increase GC responsiveness " \
384 "to changing heap conditions, at the expense of higher perf " \
385 "overhead. Time is in milliseconds.") \
386 range(1, 999) \
387 \
388 product(uintx, ShenandoahControlIntervalAdjustPeriod, 1000, EXPERIMENTAL, \
389 "The time period for one step in control loop interval " \
390 "adjustment. Lower values make adjustments faster, at the " \
391 "expense of higher perf overhead. Time is in milliseconds.") \
392 \
393 product(bool, ShenandoahVerify, false, DIAGNOSTIC, \
394 "Enable internal verification. This would catch many GC bugs, " \
395 "but it would also stall the collector during the verification, " \
396 "which prolongs the pauses and might hide other bugs.") \
397 \
398 product(intx, ShenandoahVerifyLevel, 4, DIAGNOSTIC, \
399 "Verification level, higher levels check more, taking more time. "\
400 "Accepted values are:" \
401 " 0 = basic heap checks; " \
402 " 1 = previous level, plus basic region checks; " \
403 " 2 = previous level, plus all roots; " \
404 " 3 = previous level, plus all reachable objects; " \
405 " 4 = previous level, plus all marked objects") \
406 \
407 product(uintx, ShenandoahEvacReserve, 5, EXPERIMENTAL, \
408 "How much of (young-generation) heap to reserve for " \
409 "(young-generation) evacuations. Larger values allow GC to " \
410 "evacuate more live objects on every cycle, while leaving " \
411 "less headroom for application to allocate while GC is " \
412 "evacuating and updating references. This parameter is " \
413 "consulted at the end of marking, before selecting the " \
414 "collection set. If available memory at this time is smaller " \
415 "than the indicated reserve, the bound on collection set size is "\
416 "adjusted downward. The size of a generational mixed " \
417 "evacuation collection set (comprised of both young and old " \
418 "regions) is also bounded by this parameter. In percents of " \
419 "total (young-generation) heap size.") \
420 range(1,100) \
421 \
422 product(double, ShenandoahEvacWaste, 1.2, EXPERIMENTAL, \
423 "How much waste evacuations produce within the reserved space. " \
424 "Larger values make evacuations more resilient against " \
425 "evacuation conflicts, at expense of evacuating less on each " \
426 "GC cycle. Smaller values increase the risk of evacuation " \
427 "failures, which will trigger stop-the-world Full GC passes.") \
428 range(1.0,100.0) \
429 \
430 product(double, ShenandoahOldEvacWaste, 1.4, EXPERIMENTAL, \
431 "How much waste evacuations produce within the reserved space. " \
432 "Larger values make evacuations more resilient against " \
433 "evacuation conflicts, at expense of evacuating less on each " \
434 "GC cycle. Smaller values increase the risk of evacuation " \
435 "failures, which will trigger stop-the-world Full GC passes.") \
436 range(1.0,100.0) \
437 \
438 product(double, ShenandoahPromoEvacWaste, 1.2, EXPERIMENTAL, \
439 "How much waste promotions produce within the reserved space. " \
440 "Larger values make evacuations more resilient against " \
441 "evacuation conflicts, at expense of promoting less on each " \
442 "GC cycle. Smaller values increase the risk of evacuation " \
443 "failures, which will trigger stop-the-world Full GC passes.") \
444 range(1.0,100.0) \
445 \
446 product(bool, ShenandoahEvacReserveOverflow, true, EXPERIMENTAL, \
447 "Allow evacuations to overflow the reserved space. Enabling it " \
448 "will make evacuations more resilient when evacuation " \
449 "reserve/waste is incorrect, at the risk that application " \
450 "runs out of memory too early.") \
451 \
452 product(uintx, ShenandoahOldEvacPercent, 75, EXPERIMENTAL, \
453 "The maximum evacuation to old-gen expressed as a percent of " \
454 "the total live memory within the collection set. With the " \
455 "default setting, if collection set evacuates X, no more than " \
456 "75% of X may hold objects evacuated from old or promoted to " \
457 "old from young. A value of 100 allows the entire collection " \
458 "set to be comprised of old-gen regions and young regions that " \
459 "have reached the tenure age. Larger values allow fewer mixed " \
460 "evacuations to reclaim all the garbage from old. Smaller " \
461 "values result in less variation in GC cycle times between " \
462 "young vs. mixed cycles. A value of 0 prevents mixed " \
463 "evacations from running and blocks promotion of aged regions " \
464 "by evacuation. Setting the value to 0 does not prevent " \
465 "regions from being promoted in place.") \
466 range(0,100) \
467 \
468 product(bool, ShenandoahEvacTracking, false, DIAGNOSTIC, \
469 "Collect additional metrics about evacuations. Enabling this " \
470 "tracks how many objects and how many bytes were evacuated, and " \
471 "how many were abandoned. The information will be categorized " \
472 "by thread type (worker or mutator) and evacuation type (young, " \
473 "old, or promotion.") \
474 \
475 product(uintx, ShenandoahCriticalFreeThreshold, 1, EXPERIMENTAL, \
476 "How much of the heap needs to be free after recovery cycles, " \
477 "either Degenerated or Full GC to be claimed successful. If this "\
478 "much space is not available, next recovery step would be " \
479 "triggered.") \
480 range(0, 100) \
481 \
482 product(bool, ShenandoahDegeneratedGC, true, DIAGNOSTIC, \
483 "Enable Degenerated GC as the graceful degradation step. " \
484 "Disabling this option leads to degradation to Full GC instead. " \
485 "When running in passive mode, this can be toggled to measure " \
486 "either Degenerated GC or Full GC costs.") \
487 \
488 product(uintx, ShenandoahFullGCThreshold, 3, EXPERIMENTAL, \
489 "How many back-to-back Degenerated GCs should happen before " \
490 "going to a Full GC.") \
491 \
492 product(uintx, ShenandoahNoProgressThreshold, 5, EXPERIMENTAL, \
493 "After this number of consecutive Full GCs fail to make " \
494 "progress, Shenandoah will raise out of memory errors. Note " \
495 "that progress is determined by ShenandoahCriticalFreeThreshold") \
496 \
497 product(bool, ShenandoahImplicitGCInvokesConcurrent, false, EXPERIMENTAL, \
498 "Should internally-caused GC requests invoke concurrent cycles, " \
499 "should they do the stop-the-world (Degenerated / Full GC)? " \
500 "Many heuristics automatically enable this. This option is " \
501 "similar to global ExplicitGCInvokesConcurrent.") \
502 \
503 product(bool, ShenandoahHumongousMoves, true, DIAGNOSTIC, \
504 "Allow moving humongous regions. This makes GC more resistant " \
505 "to external fragmentation that may otherwise fail other " \
506 "humongous allocations, at the expense of higher GC copying " \
507 "costs. Currently affects stop-the-world (Full) cycle only.") \
508 \
509 product(bool, ShenandoahOOMDuringEvacALot, false, DIAGNOSTIC, \
510 "Testing: simulate OOM during evacuation.") \
511 \
512 product(bool, ShenandoahAllocFailureALot, false, DIAGNOSTIC, \
513 "Testing: make lots of artificial allocation failures.") \
514 \
515 product(uintx, ShenandoahCoalesceChance, 0, DIAGNOSTIC, \
516 "Testing: Abandon remaining mixed collections with this " \
517 "likelihood. Following each mixed collection, abandon all " \
518 "remaining mixed collection candidate regions with likelihood " \
519 "ShenandoahCoalesceChance. Abandoning a mixed collection will " \
520 "cause the old regions to be made parsable, rather than being " \
521 "evacuated.") \
522 range(0, 100) \
523 \
524 product(intx, ShenandoahMarkScanPrefetch, 32, EXPERIMENTAL, \
525 "How many objects to prefetch ahead when traversing mark bitmaps."\
526 "Set to 0 to disable prefetching.") \
527 range(0, 256) \
528 \
529 product(uintx, ShenandoahMarkLoopStride, 1000, EXPERIMENTAL, \
530 "How many items to process during one marking iteration before " \
531 "checking for cancellation, yielding, etc. Larger values improve "\
532 "marking performance at expense of responsiveness.") \
533 \
534 product(uintx, ShenandoahParallelRegionStride, 0, EXPERIMENTAL, \
535 "How many regions to process at once during parallel region " \
536 "iteration. Affects heaps with lots of regions. " \
537 "Set to 0 to let Shenandoah to decide the best value.") \
538 \
539 product(size_t, ShenandoahSATBBufferSize, 1 * K, EXPERIMENTAL, \
540 "Number of entries in an SATB log buffer.") \
541 range(1, max_uintx) \
542 \
543 product(uintx, ShenandoahMaxSATBBufferFlushes, 5, EXPERIMENTAL, \
544 "How many times to maximum attempt to flush SATB buffers at the " \
545 "end of concurrent marking.") \
546 \
547 product(bool, ShenandoahSATBBarrier, true, DIAGNOSTIC, \
548 "Turn on/off SATB barriers in Shenandoah") \
549 \
550 product(bool, ShenandoahCardBarrier, false, DIAGNOSTIC, \
551 "Turn on/off card-marking post-write barrier in Shenandoah: " \
552 " true when ShenandoahGCMode is generational, false otherwise") \
553 \
554 product(bool, ShenandoahCASBarrier, true, DIAGNOSTIC, \
555 "Turn on/off CAS barriers in Shenandoah") \
556 \
557 product(bool, ShenandoahCloneBarrier, true, DIAGNOSTIC, \
558 "Turn on/off clone barriers in Shenandoah") \
559 \
560 product(bool, ShenandoahLoadRefBarrier, true, DIAGNOSTIC, \
561 "Turn on/off load-reference barriers in Shenandoah") \
562 \
563 product(bool, ShenandoahStackWatermarkBarrier, true, DIAGNOSTIC, \
564 "Turn on/off stack watermark barriers in Shenandoah") \
565 \
566 product(bool, ShenandoahCloneRuntime, false, DIAGNOSTIC, \
567 "Handle clone in runtime instead of in copy stubs.") \
568 \
569 product(bool, ShenandoahElideBarriers, true, DIAGNOSTIC, \
570 "Elide redundant Shenandoah barriers.") \
571 \
572 product(bool, ShenandoahFasterRuntimeStubs, true, DIAGNOSTIC, \
573 "Optimize register save/restore in runtime stubs.") \
574 \
575 product(bool, ShenandoahWeakRootsEarly, false, EXPERIMENTAL, \
576 "Turn off weak roots earlier than usual. TODO: Upstream!") \
577 \
578 product(int, ShenandoahReservedStackSlots, 4, EXPERIMENTAL, \
579 "How many stack slots to reserve in C2 frame for stub use.") \
580 range(4, 32) \
581 \
582 product(int, ShenandoahDelayGC, 0, EXPERIMENTAL, \
583 "Delay GC phases by this amount of milliseconds. " \
584 "Helps to measure active GC barriers costs.") \
585 \
586 develop(bool, ShenandoahVerifyOptoBarriers, trueInDebug, \
587 "Verify no missing barriers in C2.") \
588 \
589 product(uintx, ShenandoahOldCompactionReserve, 8, EXPERIMENTAL, \
590 "During generational GC, prevent promotions from filling " \
591 "this number of heap regions. These regions are reserved " \
592 "for the purpose of supporting compaction of old-gen " \
593 "memory. Otherwise, old-gen memory cannot be compacted.") \
594 range(0, 128) \
595 \
596 product(bool, ShenandoahAllowOldMarkingPreemption, true, DIAGNOSTIC, \
597 "Allow young generation collections to suspend concurrent" \
598 " marking in the old generation.") \
599 \
600 product(uintx, ShenandoahAgingCyclePeriod, 1, EXPERIMENTAL, \
601 "With generational mode, increment the age of objects and" \
602 "regions each time this many young-gen GC cycles are completed.") \
603 \
604 develop(bool, ShenandoahEnableCardStats, false, \
605 "Enable statistics collection related to clean & dirty cards") \
606 \
607 develop(int, ShenandoahCardStatsLogInterval, 50, \
608 "Log cumulative card stats every so many remembered set or " \
609 "update refs scans") \
610 \
611 product(uintx, ShenandoahMinimumOldTimeMs, 100, EXPERIMENTAL, \
612 "Minimum amount of time in milliseconds to run old collections " \
613 "before a young collection is allowed to run. This is intended " \
614 "to prevent starvation of the old collector. Setting this to " \
615 "0 will allow back to back young collections to run during old " \
616 "collections.") \
617 // end of GC_SHENANDOAH_FLAGS
618
619 #endif // SHARE_GC_SHENANDOAH_SHENANDOAH_GLOBALS_HPP