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