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 notproduct, \
35 range, \
36 constraint) \
37 \
38 product(uintx, ShenandoahGenerationalHumongousReserve, 0, EXPERIMENTAL, \
39 "(Generational mode only) What percent of the heap should be " \
40 "reserved for humongous objects if possible. Old-generation " \
41 "collections will endeavor to evacuate old-gen regions within " \
42 "this reserved area even if these regions do not contain high " \
43 "percentage of garbage. Setting a larger value will cause " \
44 "more frequent old-gen collections. A smaller value will " \
45 "increase the likelihood that humongous object allocations " \
46 "fail, resulting in stop-the-world full GCs.") \
47 range(0,100) \
48 \
49 product(double, ShenandoahMinOldGenGrowthPercent, 12.5, EXPERIMENTAL, \
50 "(Generational mode only) If the usage within old generation " \
51 "has grown by at least this percent of its live memory size " \
52 "at completion of the most recent old-generation marking " \
53 "effort, heuristics may trigger the start of a new old-gen " \
54 "collection.") \
55 range(0.0,100.0) \
56 \
57 product(uintx, ShenandoahIgnoreOldGrowthBelowPercentage,10, EXPERIMENTAL, \
58 "(Generational mode only) If the total usage of the old " \
59 "generation is smaller than this percent, we do not trigger " \
60 "old gen collections even if old has grown, except when " \
61 "ShenandoahGenerationalDoNotIgnoreGrowthAfterYoungCycles " \
62 "consecutive cycles have been completed following the " \
63 "preceding old-gen collection.") \
64 range(0,100) \
65 \
66 product(uintx, ShenandoahDoNotIgnoreGrowthAfterYoungCycles, \
67 50, EXPERIMENTAL, \
68 "(Generational mode only) Even if the usage of old generation " \
69 "is below ShenandoahIgnoreOldGrowthBelowPercentage, " \
70 "trigger an old-generation mark if old has grown and this " \
71 "many consecutive young-gen collections have been " \
72 "completed following the preceding old-gen collection.") \
73 \
74 product(bool, ShenandoahGenerationalCensusAtEvac, false, EXPERIMENTAL, \
75 "(Generational mode only) Object age census at evacuation, " \
76 "rather than during marking.") \
77 \
78 product(bool, ShenandoahGenerationalAdaptiveTenuring, true, EXPERIMENTAL, \
79 "(Generational mode only) Dynamically adapt tenuring age.") \
80 \
81 product(bool, ShenandoahGenerationalCensusIgnoreOlderCohorts, true, \
82 EXPERIMENTAL,\
83 "(Generational mode only) Ignore mortality rates older than the " \
84 "oldest cohort under the tenuring age for the last cycle." ) \
85 \
86 product(uintx, ShenandoahGenerationalMinTenuringAge, 1, EXPERIMENTAL, \
87 "(Generational mode only) Floor for adaptive tenuring age. " \
88 "Setting floor and ceiling to the same value fixes the tenuring " \
89 "age; setting both to 1 simulates a poor approximation to " \
90 "AlwaysTenure, and setting both to 16 simulates NeverTenure.") \
91 range(1,16) \
92 \
93 product(uintx, ShenandoahGenerationalMaxTenuringAge, 15, EXPERIMENTAL, \
94 "(Generational mode only) Ceiling for adaptive tenuring age. " \
95 "Setting floor and ceiling to the same value fixes the tenuring " \
96 "age; setting both to 1 simulates a poor approximation to " \
97 "AlwaysTenure, and setting both to 16 simulates NeverTenure.") \
98 range(1,16) \
99 \
100 product(double, ShenandoahGenerationalTenuringMortalityRateThreshold, \
101 0.1, EXPERIMENTAL, \
102 "(Generational mode only) Cohort mortality rates below this " \
103 "value will be treated as indicative of longevity, leading to " \
104 "tenuring. A lower value delays tenuring, a higher value hastens "\
105 "it. Used only when ShenandoahGenerationalhenAdaptiveTenuring is "\
106 "enabled.") \
107 range(0.001,0.999) \
108 \
109 product(size_t, ShenandoahGenerationalTenuringCohortPopulationThreshold, \
110 4*K, EXPERIMENTAL, \
111 "(Generational mode only) Cohorts whose population is lower than "\
112 "this value in the previous census are ignored wrt tenuring " \
113 "decisions. Effectively this makes then tenurable as soon as all "\
114 "older cohorts are. Set this value to the largest cohort " \
115 "population volume that you are comfortable ignoring when making "\
116 "tenuring decisions.") \
117 \
118 product(size_t, ShenandoahRegionSize, 0, EXPERIMENTAL, \
119 "Static heap region size. Set zero to enable automatic sizing.") \
120 \
121 product(size_t, ShenandoahTargetNumRegions, 2048, EXPERIMENTAL, \
122 "With automatic region sizing, this is the approximate number " \
123 "of regions that would be used, within min/max region size " \
124 "limits.") \
125 \
126 product(size_t, ShenandoahMinRegionSize, 256 * K, EXPERIMENTAL, \
127 "With automatic region sizing, the regions would be at least " \
128 "this large.") \
129 \
130 product(size_t, ShenandoahMaxRegionSize, 32 * M, EXPERIMENTAL, \
131 "With automatic region sizing, the regions would be at most " \
132 "this large.") \
133 \
134 product(intx, ShenandoahHumongousThreshold, 100, EXPERIMENTAL, \
135 "Humongous objects are allocated in separate regions. " \
136 "This setting defines how large the object should be to be " \
137 "deemed humongous. Value is in percents of heap region size. " \
138 "This also caps the maximum TLAB size.") \
139 range(1, 100) \
140 \
141 product(ccstr, ShenandoahGCMode, "satb", \
142 "GC mode to use. Among other things, this defines which " \
143 "barriers are in in use. Possible values are:" \
144 " satb - snapshot-at-the-beginning concurrent GC (three pass mark-evac-update);" \
145 " iu - incremental-update concurrent GC (three pass mark-evac-update);" \
146 " passive - stop the world GC only (either degenerated or full);" \
147 " generational - generational concurrent GC") \
148 \
149 product(ccstr, ShenandoahGCHeuristics, "adaptive", \
150 "GC heuristics to use. This fine-tunes the GC mode selected, " \
151 "by choosing when to start the GC, how much to process on each " \
152 "cycle, and what other features to automatically enable. " \
153 "Possible values are:" \
154 " adaptive - adapt to maintain the given amount of free heap " \
155 "at all times, even during the GC cycle;" \
156 " static - trigger GC when free heap falls below the threshold;" \
157 " aggressive - run GC continuously, try to evacuate everything;" \
158 " compact - run GC more frequently and with deeper targets to " \
159 "free up more memory.") \
160 \
161 product(uintx, ShenandoahExpeditePromotionsThreshold, 5, EXPERIMENTAL, \
162 "When Shenandoah expects to promote at least this percentage " \
163 "of the young generation, trigger a young collection to " \
164 "expedite these promotions.") \
165 range(0,100) \
166 \
167 product(uintx, ShenandoahExpediteMixedThreshold, 10, EXPERIMENTAL, \
168 "When there are this many old regions waiting to be collected, " \
169 "trigger a mixed collection immediately.") \
170 \
171 product(uintx, ShenandoahGarbageThreshold, 25, EXPERIMENTAL, \
172 "How much garbage a region has to contain before it would be " \
173 "taken for collection. This a guideline only, as GC heuristics " \
174 "may select the region for collection even if it has little " \
175 "garbage. This also affects how much internal fragmentation the " \
176 "collector accepts. In percents of heap region size.") \
177 range(0,100) \
178 \
179 product(uintx, ShenandoahOldGarbageThreshold, 15, EXPERIMENTAL, \
180 "How much garbage an old region has to contain before it would " \
181 "be taken for collection.") \
182 range(0,100) \
183 \
184 product(uintx, ShenandoahIgnoreGarbageThreshold, 5, EXPERIMENTAL, \
185 "When less than this amount of garbage (as a percentage of " \
186 "region size) exists within a region, the region will not be " \
187 "added to the collection set, even when the heuristic has " \
188 "chosen to aggressively add regions with less than " \
189 "ShenandoahGarbageThreshold amount of garbage into the " \
190 "collection set.") \
191 range(0,100) \
192 \
193 product(uintx, ShenandoahInitFreeThreshold, 70, EXPERIMENTAL, \
194 "When less than this amount of memory is free within the" \
195 "heap or generation, trigger a learning cycle if we are " \
196 "in learning mode. Learning mode happens during initialization " \
197 "and following a drastic state change, such as following a " \
198 "degenerated or Full GC cycle. In percents of soft max " \
199 "heap size.") \
200 range(0,100) \
201 \
202 product(uintx, ShenandoahMinFreeThreshold, 10, EXPERIMENTAL, \
203 "Percentage of free heap memory (or young generation, in " \
204 "generational mode) below which most heuristics trigger " \
205 "collection independent of other triggers. Provides a safety " \
206 "margin for many heuristics. In percents of (soft) max heap " \
207 "size.") \
208 range(0,100) \
209 \
210 product(uintx, ShenandoahAllocationThreshold, 0, EXPERIMENTAL, \
211 "How many new allocations should happen since the last GC cycle " \
212 "before some heuristics trigger the collection. In percents of " \
213 "(soft) max heap size. Set to zero to effectively disable.") \
214 range(0,100) \
215 \
216 product(uintx, ShenandoahAllocSpikeFactor, 5, EXPERIMENTAL, \
217 "How much of heap should some heuristics reserve for absorbing " \
218 "the allocation spikes. Larger value wastes more memory in " \
219 "non-emergency cases, but provides more safety in emergency " \
220 "cases. In percents of (soft) max heap size.") \
221 range(0,100) \
222 \
223 product(uintx, ShenandoahLearningSteps, 10, EXPERIMENTAL, \
224 "The number of cycles some heuristics take to collect in order " \
225 "to learn application and GC performance.") \
226 range(0,100) \
227 \
228 product(uintx, ShenandoahImmediateThreshold, 70, EXPERIMENTAL, \
229 "The cycle may shortcut when enough garbage can be reclaimed " \
230 "from the immediate garbage (completely garbage regions). " \
231 "In percents of total garbage found. Setting this threshold " \
232 "to 100 effectively disables the shortcut.") \
233 range(0,100) \
234 \
235 product(uintx, ShenandoahAdaptiveSampleFrequencyHz, 10, EXPERIMENTAL, \
236 "The number of times per second to update the allocation rate " \
237 "moving average.") \
238 \
239 product(uintx, ShenandoahAdaptiveSampleSizeSeconds, 10, EXPERIMENTAL, \
240 "The size of the moving window over which the average " \
241 "allocation rate is maintained. The total number of samples " \
242 "is the product of this number and the sample frequency.") \
243 \
244 product(double, ShenandoahAdaptiveInitialConfidence, 1.8, EXPERIMENTAL, \
245 "The number of standard deviations used to determine an initial " \
246 "margin of error for the average cycle time and average " \
247 "allocation rate. Increasing this value will cause the " \
248 "heuristic to initiate more concurrent cycles." ) \
249 \
250 product(double, ShenandoahAdaptiveInitialSpikeThreshold, 1.8, EXPERIMENTAL, \
251 "If the most recently sampled allocation rate is more than " \
252 "this many standard deviations away from the moving average, " \
253 "then a cycle is initiated. This value controls how sensitive " \
254 "the heuristic is to allocation spikes. Decreasing this number " \
255 "increases the sensitivity. ") \
256 \
257 product(double, ShenandoahAdaptiveDecayFactor, 0.1, EXPERIMENTAL, \
258 "The decay factor (alpha) used for values in the weighted " \
259 "moving average of cycle time and allocation rate. " \
260 "Larger values give more weight to recent values.") \
261 range(0,1.0) \
262 \
263 product(bool, ShenandoahAdaptiveIgnoreShortCycles, true, EXPERIMENTAL, \
264 "The adaptive heuristic tracks a moving average of cycle " \
265 "times in order to start a gc before memory is exhausted. " \
266 "In some cases, Shenandoah may skip the evacuation and update " \
267 "reference phases, resulting in a shorter cycle. These may skew " \
268 "the average cycle time downward and may cause the heuristic " \
269 "to wait too long to start a cycle. Disabling this will have " \
270 "the gc run less often, which will reduce CPU utilization, but" \
271 "increase the risk of degenerated cycles.") \
272 \
273 product(uintx, ShenandoahGuaranteedGCInterval, 5*60*1000, EXPERIMENTAL, \
274 "Many heuristics would guarantee a concurrent GC cycle at " \
275 "least with this interval. This is useful when large idle " \
276 "intervals are present, where GC can run without stealing " \
277 "time from active application. Time is in milliseconds. " \
278 "Setting this to 0 disables the feature.") \
279 \
280 product(uintx, ShenandoahGuaranteedOldGCInterval, 10*60*1000, EXPERIMENTAL, \
281 "Run a collection of the old generation at least this often. " \
282 "Heuristics may trigger collections more frequently. Time is in " \
283 "milliseconds. Setting this to 0 disables the feature.") \
284 \
285 product(uintx, ShenandoahGuaranteedYoungGCInterval, 5*60*1000, EXPERIMENTAL, \
286 "Run a collection of the young generation at least this often. " \
287 "Heuristics may trigger collections more frequently. Time is in " \
288 "milliseconds. Setting this to 0 disables the feature.") \
289 \
290 product(bool, ShenandoahAlwaysClearSoftRefs, false, EXPERIMENTAL, \
291 "Unconditionally clear soft references, instead of using any " \
292 "other cleanup policy. This minimizes footprint at expense of" \
293 "more soft reference churn in applications.") \
294 \
295 product(bool, ShenandoahUncommit, true, EXPERIMENTAL, \
296 "Allow to uncommit memory under unused regions and metadata. " \
297 "This optimizes footprint at expense of allocation latency in " \
298 "regions that require committing back. Uncommits would be " \
299 "disabled by some heuristics, or with static heap size.") \
300 \
301 product(uintx, ShenandoahUncommitDelay, 5*60*1000, EXPERIMENTAL, \
302 "Uncommit memory for regions that were not used for more than " \
303 "this time. First use after that would incur allocation stalls. " \
304 "Actively used regions would never be uncommitted, because they " \
305 "do not become unused longer than this delay. Time is in " \
306 "milliseconds. Setting this delay to 0 effectively uncommits " \
307 "regions almost immediately after they become unused.") \
308 \
309 product(bool, ShenandoahRegionSampling, false, EXPERIMENTAL, \
310 "Provide heap region sampling data via jvmstat.") \
311 \
312 product(int, ShenandoahRegionSamplingRate, 40, EXPERIMENTAL, \
313 "Sampling rate for heap region sampling. In milliseconds between "\
314 "the samples. Higher values provide more fidelity, at expense " \
315 "of more sampling overhead.") \
316 \
317 product(uintx, ShenandoahControlIntervalMin, 1, EXPERIMENTAL, \
318 "The minimum sleep interval for the control loop that drives " \
319 "the cycles. Lower values would increase GC responsiveness " \
320 "to changing heap conditions, at the expense of higher perf " \
321 "overhead. Time is in milliseconds.") \
322 \
323 product(uintx, ShenandoahControlIntervalMax, 10, EXPERIMENTAL, \
324 "The maximum sleep interval for control loop that drives " \
325 "the cycles. Lower values would increase GC responsiveness " \
326 "to changing heap conditions, at the expense of higher perf " \
327 "overhead. Time is in milliseconds.") \
328 \
329 product(uintx, ShenandoahControlIntervalAdjustPeriod, 1000, EXPERIMENTAL, \
330 "The time period for one step in control loop interval " \
331 "adjustment. Lower values make adjustments faster, at the " \
332 "expense of higher perf overhead. Time is in milliseconds.") \
333 \
334 product(bool, ShenandoahVerify, false, DIAGNOSTIC, \
335 "Enable internal verification. This would catch many GC bugs, " \
336 "but it would also stall the collector during the verification, " \
337 "which prolongs the pauses and might hide other bugs.") \
338 \
339 product(intx, ShenandoahVerifyLevel, 4, DIAGNOSTIC, \
340 "Verification level, higher levels check more, taking more time. "\
341 "Accepted values are:" \
342 " 0 = basic heap checks; " \
343 " 1 = previous level, plus basic region checks; " \
344 " 2 = previous level, plus all roots; " \
345 " 3 = previous level, plus all reachable objects; " \
346 " 4 = previous level, plus all marked objects") \
347 \
348 product(uintx, ShenandoahEvacReserve, 5, EXPERIMENTAL, \
349 "How much of (young-generation) heap to reserve for " \
350 "(young-generation) evacuations. Larger values allow GC to " \
351 "evacuate more live objects on every cycle, while leaving " \
352 "less headroom for application to allocate while GC is " \
353 "evacuating and updating references. This parameter is " \
354 "consulted at the end of marking, before selecting the " \
355 "collection set. If available memory at this time is smaller " \
356 "than the indicated reserve, the bound on collection set size is "\
357 "adjusted downward. The size of a generational mixed " \
358 "evacuation collection set (comprised of both young and old " \
359 "regions) is also bounded by this parameter. In percents of " \
360 "total (young-generation) heap size.") \
361 range(1,100) \
362 \
363 product(double, ShenandoahEvacWaste, 1.2, EXPERIMENTAL, \
364 "How much waste evacuations produce within the reserved space. " \
365 "Larger values make evacuations more resilient against " \
366 "evacuation conflicts, at expense of evacuating less on each " \
367 "GC cycle. Smaller values increase the risk of evacuation " \
368 "failures, which will trigger stop-the-world Full GC passes.") \
369 range(1.0,100.0) \
370 \
371 product(double, ShenandoahOldEvacWaste, 1.4, EXPERIMENTAL, \
372 "How much waste evacuations produce within the reserved space. " \
373 "Larger values make evacuations more resilient against " \
374 "evacuation conflicts, at expense of evacuating less on each " \
375 "GC cycle. Smaller values increase the risk of evacuation " \
376 "failures, which will trigger stop-the-world Full GC passes.") \
377 range(1.0,100.0) \
378 \
379 product(double, ShenandoahPromoEvacWaste, 1.2, EXPERIMENTAL, \
380 "How much waste promotions produce within the reserved space. " \
381 "Larger values make evacuations more resilient against " \
382 "evacuation conflicts, at expense of promoting less on each " \
383 "GC cycle. Smaller values increase the risk of evacuation " \
384 "failures, which will trigger stop-the-world Full GC passes.") \
385 range(1.0,100.0) \
386 \
387 product(uintx, ShenandoahMaxEvacLABRatio, 0, EXPERIMENTAL, \
388 "Potentially, each running thread maintains a PLAB for " \
389 "evacuating objects into old-gen memory and a GCLAB for " \
390 "evacuating objects into young-gen memory. Each time a thread " \
391 "exhausts its PLAB or GCLAB, a new local buffer is allocated. " \
392 "By default, the new buffer is twice the size of the previous " \
393 "buffer. The sizes are reset to the minimum at the start of " \
394 "each GC pass. This parameter limits the growth of evacuation " \
395 "buffer sizes to its value multiplied by the minimum buffer " \
396 "size. A higher value allows evacuation allocations to be more " \
397 "efficient because less synchronization is required by " \
398 "individual threads. However, a larger value increases the " \
399 "likelihood of evacuation failures, leading to long " \
400 "stop-the-world pauses. This is because a large value " \
401 "allows individual threads to consume large percentages of " \
402 "the total evacuation budget without necessarily effectively " \
403 "filling their local evacuation buffers with evacuated " \
404 "objects. A value of zero means no maximum size is enforced.") \
405 range(0, 1024) \
406 \
407 product(bool, ShenandoahEvacReserveOverflow, true, EXPERIMENTAL, \
408 "Allow evacuations to overflow the reserved space. Enabling it " \
409 "will make evacuations more resilient when evacuation " \
410 "reserve/waste is incorrect, at the risk that application " \
411 "runs out of memory too early.") \
412 \
413 product(uintx, ShenandoahOldEvacRatioPercent, 75, EXPERIMENTAL, \
414 "The maximum proportion of evacuation from old-gen memory, " \
415 "expressed as a percentage. The default value 75 denotes that no" \
416 "more than 75% of the collection set evacuation workload may be " \
417 "towards evacuation of old-gen heap regions. This limits both the"\
418 "promotion of aged regions and the compaction of existing old " \
419 "regions. A value of 75 denotes that the total evacuation work" \
420 "may increase to up to four times the young gen evacuation work." \
421 "A larger value allows quicker promotion and allows" \
422 "a smaller number of mixed evacuations to process " \
423 "the entire list of old-gen collection candidates at the cost " \
424 "of an increased disruption of the normal cadence of young-gen " \
425 "collections. A value of 100 allows a mixed evacuation to " \
426 "focus entirely on old-gen memory, allowing no young-gen " \
427 "regions to be collected, likely resulting in subsequent " \
428 "allocation failures because the allocation pool is not " \
429 "replenished. A value of 0 allows a mixed evacuation to" \
430 "focus entirely on young-gen memory, allowing no old-gen " \
431 "regions to be collected, likely resulting in subsequent " \
432 "promotion failures and triggering of stop-the-world full GC " \
433 "events.") \
434 range(0,100) \
435 \
436 product(uintx, ShenandoahMinYoungPercentage, 20, EXPERIMENTAL, \
437 "The minimum percentage of the heap to use for the young " \
438 "generation. Heuristics will not adjust the young generation " \
439 "to be less than this.") \
440 range(0, 100) \
441 \
442 product(uintx, ShenandoahMaxYoungPercentage, 100, EXPERIMENTAL, \
443 "The maximum percentage of the heap to use for the young " \
444 "generation. Heuristics will not adjust the young generation " \
445 "to be more than this.") \
446 range(0, 100) \
447 \
448 product(bool, ShenandoahPacing, true, EXPERIMENTAL, \
449 "Pace application allocations to give GC chance to start " \
450 "and complete before allocation failure is reached.") \
451 \
452 product(uintx, ShenandoahPacingMaxDelay, 10, EXPERIMENTAL, \
453 "Max delay for pacing application allocations. Larger values " \
454 "provide more resilience against out of memory, at expense at " \
455 "hiding the GC latencies in the allocation path. Time is in " \
456 "milliseconds. Setting it to arbitrarily large value makes " \
457 "GC effectively stall the threads indefinitely instead of going " \
458 "to degenerated or Full GC.") \
459 \
460 product(uintx, ShenandoahPacingIdleSlack, 2, EXPERIMENTAL, \
461 "How much of heap counted as non-taxable allocations during idle "\
462 "phases. Larger value makes the pacing milder when collector is " \
463 "idle, requiring less rendezvous with control thread. Lower " \
464 "value makes the pacing control less responsive to out-of-cycle " \
465 "allocs. In percent of total heap size.") \
466 range(0, 100) \
467 \
468 product(uintx, ShenandoahPacingCycleSlack, 10, EXPERIMENTAL, \
469 "How much of free space to take as non-taxable allocations " \
470 "the GC cycle. Larger value makes the pacing milder at the " \
471 "beginning of the GC cycle. Lower value makes the pacing less " \
472 "uniform during the cycle. In percent of free space.") \
473 range(0, 100) \
474 \
475 product(double, ShenandoahPacingSurcharge, 1.1, EXPERIMENTAL, \
476 "Additional pacing tax surcharge to help unclutter the heap. " \
477 "Larger values makes the pacing more aggressive. Lower values " \
478 "risk GC cycles finish with less memory than were available at " \
479 "the beginning of it.") \
480 range(1.0, 100.0) \
481 \
482 product(uintx, ShenandoahCriticalFreeThreshold, 1, EXPERIMENTAL, \
483 "How much of the heap needs to be free after recovery cycles, " \
484 "either Degenerated or Full GC to be claimed successful. If this "\
485 "much space is not available, next recovery step would be " \
486 "triggered.") \
487 range(0, 100) \
488 \
489 product(bool, ShenandoahDegeneratedGC, true, DIAGNOSTIC, \
490 "Enable Degenerated GC as the graceful degradation step. " \
491 "Disabling this option leads to degradation to Full GC instead. " \
492 "When running in passive mode, this can be toggled to measure " \
493 "either Degenerated GC or Full GC costs.") \
494 \
495 product(uintx, ShenandoahFullGCThreshold, 3, EXPERIMENTAL, \
496 "How many back-to-back Degenerated GCs should happen before " \
497 "going to a Full GC.") \
498 \
499 product(uintx, ShenandoahNoProgressThreshold, 5, EXPERIMENTAL, \
500 "After this number of consecutive Full GCs fail to make " \
501 "progress, Shenandoah will raise out of memory errors. Note " \
502 "that progress is determined by ShenandoahCriticalFreeThreshold") \
503 \
504 product(bool, ShenandoahImplicitGCInvokesConcurrent, false, EXPERIMENTAL, \
505 "Should internally-caused GC requests invoke concurrent cycles, " \
506 "should they do the stop-the-world (Degenerated / Full GC)? " \
507 "Many heuristics automatically enable this. This option is " \
508 "similar to global ExplicitGCInvokesConcurrent.") \
509 \
510 product(bool, ShenandoahHumongousMoves, true, DIAGNOSTIC, \
511 "Allow moving humongous regions. This makes GC more resistant " \
512 "to external fragmentation that may otherwise fail other " \
513 "humongous allocations, at the expense of higher GC copying " \
514 "costs. Currently affects stop-the-world (Full) cycle only.") \
515 \
516 product(bool, ShenandoahOOMDuringEvacALot, false, DIAGNOSTIC, \
517 "Testing: simulate OOM during evacuation.") \
518 \
519 product(bool, ShenandoahAllocFailureALot, false, DIAGNOSTIC, \
520 "Testing: make lots of artificial allocation failures.") \
521 \
522 product(uintx, ShenandoahCoalesceChance, 0, DIAGNOSTIC, \
523 "Testing: Abandon remaining mixed collections with this " \
524 "likelihood. Following each mixed collection, abandon all " \
525 "remaining mixed collection candidate regions with likelihood " \
526 "ShenandoahCoalesceChance. Abandoning a mixed collection will " \
527 "cause the old regions to be made parsable, rather than being " \
528 "evacuated.") \
529 range(0, 100) \
530 \
531 product(intx, ShenandoahMarkScanPrefetch, 32, EXPERIMENTAL, \
532 "How many objects to prefetch ahead when traversing mark bitmaps."\
533 "Set to 0 to disable prefetching.") \
534 range(0, 256) \
535 \
536 product(uintx, ShenandoahMarkLoopStride, 1000, EXPERIMENTAL, \
537 "How many items to process during one marking iteration before " \
538 "checking for cancellation, yielding, etc. Larger values improve "\
539 "marking performance at expense of responsiveness.") \
540 \
541 product(uintx, ShenandoahParallelRegionStride, 1024, EXPERIMENTAL, \
542 "How many regions to process at once during parallel region " \
543 "iteration. Affects heaps with lots of regions.") \
544 \
545 product(size_t, ShenandoahSATBBufferSize, 1 * K, EXPERIMENTAL, \
546 "Number of entries in an SATB log buffer.") \
547 range(1, max_uintx) \
548 \
549 product(uintx, ShenandoahMaxSATBBufferFlushes, 5, EXPERIMENTAL, \
550 "How many times to maximum attempt to flush SATB buffers at the " \
551 "end of concurrent marking.") \
552 \
553 product(bool, ShenandoahSATBBarrier, true, DIAGNOSTIC, \
554 "Turn on/off SATB barriers in Shenandoah") \
555 \
556 product(bool, ShenandoahIUBarrier, false, DIAGNOSTIC, \
557 "Turn on/off I-U barriers barriers in Shenandoah") \
558 \
559 product(bool, ShenandoahCardBarrier, false, DIAGNOSTIC, \
560 "Turn on/off card-marking post-write barrier in Shenandoah: " \
561 " true when ShenandoahGCMode is generational, false otherwise") \
562 \
563 product(bool, ShenandoahCASBarrier, true, DIAGNOSTIC, \
564 "Turn on/off CAS barriers in Shenandoah") \
565 \
566 product(bool, ShenandoahCloneBarrier, true, DIAGNOSTIC, \
567 "Turn on/off clone barriers in Shenandoah") \
568 \
569 product(bool, ShenandoahLoadRefBarrier, true, DIAGNOSTIC, \
570 "Turn on/off load-reference barriers in Shenandoah") \
571 \
572 product(bool, ShenandoahStackWatermarkBarrier, true, DIAGNOSTIC, \
573 "Turn on/off stack watermark barriers in Shenandoah") \
574 \
575 develop(bool, ShenandoahVerifyOptoBarriers, trueInDebug, \
576 "Verify no missing barriers in C2.") \
577 \
578 product(uintx, ShenandoahOldCompactionReserve, 8, EXPERIMENTAL, \
579 "During generational GC, prevent promotions from filling " \
580 "this number of heap regions. These regions are reserved " \
581 "for the purpose of supporting compaction of old-gen " \
582 "memory. Otherwise, old-gen memory cannot be compacted.") \
583 range(0, 128) \
584 \
585 product(bool, ShenandoahAllowOldMarkingPreemption, true, DIAGNOSTIC, \
586 "Allow young generation collections to suspend concurrent" \
587 " marking in the old generation.") \
588 \
589 product(uintx, ShenandoahAgingCyclePeriod, 1, EXPERIMENTAL, \
590 "With generational mode, increment the age of objects and" \
591 "regions each time this many young-gen GC cycles are completed.") \
592 \
593 notproduct(bool, ShenandoahEnableCardStats, false, \
594 "Enable statistics collection related to clean & dirty cards") \
595 \
596 notproduct(int, ShenandoahCardStatsLogInterval, 50, \
597 "Log cumulative card stats every so many remembered set or " \
598 "update refs scans") \
599 \
600 product(uintx, ShenandoahMinimumOldMarkTimeMs, 100, EXPERIMENTAL, \
601 "Minimum amount of time in milliseconds to run old marking " \
602 "before a young collection is allowed to run. This is intended " \
603 "to prevent starvation of the old collector. Setting this to " \
604 "0 will allow back to back young collections to run during old " \
605 "marking.") \
606 // end of GC_SHENANDOAH_FLAGS
607
608 #endif // SHARE_GC_SHENANDOAH_SHENANDOAH_GLOBALS_HPP