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, ShenandoahUnloadClassesFrequency, 1, EXPERIMENTAL, \
172 "Unload the classes every Nth cycle. Normally affects concurrent "\
173 "GC cycles, as degenerated and full GCs would try to unload " \
174 "classes regardless. Set to zero to disable class unloading.") \
175 \
176 product(uintx, ShenandoahGarbageThreshold, 25, EXPERIMENTAL, \
177 "How much garbage a region has to contain before it would be " \
178 "taken for collection. This a guideline only, as GC heuristics " \
179 "may select the region for collection even if it has little " \
180 "garbage. This also affects how much internal fragmentation the " \
181 "collector accepts. In percents of heap region size.") \
182 range(0,100) \
183 \
184 product(uintx, ShenandoahOldGarbageThreshold, 15, EXPERIMENTAL, \
185 "How much garbage an old region has to contain before it would " \
186 "be taken for collection.") \
187 range(0,100) \
188 \
189 product(uintx, ShenandoahIgnoreGarbageThreshold, 5, EXPERIMENTAL, \
190 "When less than this amount of garbage (as a percentage of " \
191 "region size) exists within a region, the region will not be " \
192 "added to the collection set, even when the heuristic has " \
193 "chosen to aggressively add regions with less than " \
194 "ShenandoahGarbageThreshold amount of garbage into the " \
195 "collection set.") \
196 range(0,100) \
197 \
198 product(uintx, ShenandoahInitFreeThreshold, 70, EXPERIMENTAL, \
199 "When less than this amount of memory is free within the" \
200 "heap or generation, trigger a learning cycle if we are " \
201 "in learning mode. Learning mode happens during initialization " \
202 "and following a drastic state change, such as following a " \
203 "degenerated or Full GC cycle. In percents of soft max " \
204 "heap size.") \
205 range(0,100) \
206 \
207 product(uintx, ShenandoahMinFreeThreshold, 10, EXPERIMENTAL, \
208 "Percentage of free heap memory (or young generation, in " \
209 "generational mode) below which most heuristics trigger " \
210 "collection independent of other triggers. Provides a safety " \
211 "margin for many heuristics. In percents of (soft) max heap " \
212 "size.") \
213 range(0,100) \
214 \
215 product(uintx, ShenandoahAllocationThreshold, 0, EXPERIMENTAL, \
216 "How many new allocations should happen since the last GC cycle " \
217 "before some heuristics trigger the collection. In percents of " \
218 "(soft) max heap size. Set to zero to effectively disable.") \
219 range(0,100) \
220 \
221 product(uintx, ShenandoahAllocSpikeFactor, 5, EXPERIMENTAL, \
222 "How much of heap should some heuristics reserve for absorbing " \
223 "the allocation spikes. Larger value wastes more memory in " \
224 "non-emergency cases, but provides more safety in emergency " \
225 "cases. In percents of (soft) max heap size.") \
226 range(0,100) \
227 \
228 product(uintx, ShenandoahLearningSteps, 10, EXPERIMENTAL, \
229 "The number of cycles some heuristics take to collect in order " \
230 "to learn application and GC performance.") \
231 range(0,100) \
232 \
233 product(uintx, ShenandoahImmediateThreshold, 70, EXPERIMENTAL, \
234 "The cycle may shortcut when enough garbage can be reclaimed " \
235 "from the immediate garbage (completely garbage regions). " \
236 "In percents of total garbage found. Setting this threshold " \
237 "to 100 effectively disables the shortcut.") \
238 range(0,100) \
239 \
240 product(uintx, ShenandoahAdaptiveSampleFrequencyHz, 10, EXPERIMENTAL, \
241 "The number of times per second to update the allocation rate " \
242 "moving average.") \
243 \
244 product(uintx, ShenandoahAdaptiveSampleSizeSeconds, 10, EXPERIMENTAL, \
245 "The size of the moving window over which the average " \
246 "allocation rate is maintained. The total number of samples " \
247 "is the product of this number and the sample frequency.") \
248 \
249 product(double, ShenandoahAdaptiveInitialConfidence, 1.8, EXPERIMENTAL, \
250 "The number of standard deviations used to determine an initial " \
251 "margin of error for the average cycle time and average " \
252 "allocation rate. Increasing this value will cause the " \
253 "heuristic to initiate more concurrent cycles." ) \
254 \
255 product(double, ShenandoahAdaptiveInitialSpikeThreshold, 1.8, EXPERIMENTAL, \
256 "If the most recently sampled allocation rate is more than " \
257 "this many standard deviations away from the moving average, " \
258 "then a cycle is initiated. This value controls how sensitive " \
259 "the heuristic is to allocation spikes. Decreasing this number " \
260 "increases the sensitivity. ") \
261 \
262 product(double, ShenandoahAdaptiveDecayFactor, 0.1, EXPERIMENTAL, \
263 "The decay factor (alpha) used for values in the weighted " \
264 "moving average of cycle time and allocation rate. " \
265 "Larger values give more weight to recent values.") \
266 range(0,1.0) \
267 \
268 product(bool, ShenandoahAdaptiveIgnoreShortCycles, true, EXPERIMENTAL, \
269 "The adaptive heuristic tracks a moving average of cycle " \
270 "times in order to start a gc before memory is exhausted. " \
271 "In some cases, Shenandoah may skip the evacuation and update " \
272 "reference phases, resulting in a shorter cycle. These may skew " \
273 "the average cycle time downward and may cause the heuristic " \
274 "to wait too long to start a cycle. Disabling this will have " \
275 "the gc run less often, which will reduce CPU utilization, but" \
276 "increase the risk of degenerated cycles.") \
277 \
278 product(uintx, ShenandoahGuaranteedGCInterval, 5*60*1000, EXPERIMENTAL, \
279 "Many heuristics would guarantee a concurrent GC cycle at " \
280 "least with this interval. This is useful when large idle " \
281 "intervals are present, where GC can run without stealing " \
282 "time from active application. Time is in milliseconds. " \
283 "Setting this to 0 disables the feature.") \
284 \
285 product(uintx, ShenandoahGuaranteedOldGCInterval, 10*60*1000, EXPERIMENTAL, \
286 "Run a collection of the old 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(uintx, ShenandoahGuaranteedYoungGCInterval, 5*60*1000, EXPERIMENTAL, \
291 "Run a collection of the young generation at least this often. " \
292 "Heuristics may trigger collections more frequently. Time is in " \
293 "milliseconds. Setting this to 0 disables the feature.") \
294 \
295 product(bool, ShenandoahAlwaysClearSoftRefs, false, EXPERIMENTAL, \
296 "Unconditionally clear soft references, instead of using any " \
297 "other cleanup policy. This minimizes footprint at expense of" \
298 "more soft reference churn in applications.") \
299 \
300 product(bool, ShenandoahUncommit, true, EXPERIMENTAL, \
301 "Allow to uncommit memory under unused regions and metadata. " \
302 "This optimizes footprint at expense of allocation latency in " \
303 "regions that require committing back. Uncommits would be " \
304 "disabled by some heuristics, or with static heap size.") \
305 \
306 product(uintx, ShenandoahUncommitDelay, 5*60*1000, EXPERIMENTAL, \
307 "Uncommit memory for regions that were not used for more than " \
308 "this time. First use after that would incur allocation stalls. " \
309 "Actively used regions would never be uncommitted, because they " \
310 "do not become unused longer than this delay. Time is in " \
311 "milliseconds. Setting this delay to 0 effectively uncommits " \
312 "regions almost immediately after they become unused.") \
313 \
314 product(bool, ShenandoahRegionSampling, false, EXPERIMENTAL, \
315 "Provide heap region sampling data via jvmstat.") \
316 \
317 product(int, ShenandoahRegionSamplingRate, 40, EXPERIMENTAL, \
318 "Sampling rate for heap region sampling. In milliseconds between "\
319 "the samples. Higher values provide more fidelity, at expense " \
320 "of more sampling overhead.") \
321 \
322 product(uintx, ShenandoahControlIntervalMin, 1, EXPERIMENTAL, \
323 "The minimum sleep interval for the control loop that drives " \
324 "the cycles. Lower values would increase GC responsiveness " \
325 "to changing heap conditions, at the expense of higher perf " \
326 "overhead. Time is in milliseconds.") \
327 \
328 product(uintx, ShenandoahControlIntervalMax, 10, EXPERIMENTAL, \
329 "The maximum sleep interval for control loop that drives " \
330 "the cycles. Lower values would increase GC responsiveness " \
331 "to changing heap conditions, at the expense of higher perf " \
332 "overhead. Time is in milliseconds.") \
333 \
334 product(uintx, ShenandoahControlIntervalAdjustPeriod, 1000, EXPERIMENTAL, \
335 "The time period for one step in control loop interval " \
336 "adjustment. Lower values make adjustments faster, at the " \
337 "expense of higher perf overhead. Time is in milliseconds.") \
338 \
339 product(bool, ShenandoahVerify, false, DIAGNOSTIC, \
340 "Enable internal verification. This would catch many GC bugs, " \
341 "but it would also stall the collector during the verification, " \
342 "which prolongs the pauses and might hide other bugs.") \
343 \
344 product(intx, ShenandoahVerifyLevel, 4, DIAGNOSTIC, \
345 "Verification level, higher levels check more, taking more time. "\
346 "Accepted values are:" \
347 " 0 = basic heap checks; " \
348 " 1 = previous level, plus basic region checks; " \
349 " 2 = previous level, plus all roots; " \
350 " 3 = previous level, plus all reachable objects; " \
351 " 4 = previous level, plus all marked objects") \
352 \
353 product(bool, ShenandoahElasticTLAB, true, DIAGNOSTIC, \
354 "Use Elastic TLABs with Shenandoah. This allows Shenandoah to " \
355 "decrease the size of a TLAB to fit in a region's remaining space") \
356 \
357 product(uintx, ShenandoahEvacReserve, 5, EXPERIMENTAL, \
358 "How much of (young-generation) heap to reserve for " \
359 "(young-generation) evacuations. Larger values allow GC to " \
360 "evacuate more live objects on every cycle, while leaving " \
361 "less headroom for application to allocate while GC is " \
362 "evacuating and updating references. This parameter is " \
363 "consulted at the end of marking, before selecting the " \
364 "collection set. If available memory at this time is smaller " \
365 "than the indicated reserve, the bound on collection set size is "\
366 "adjusted downward. The size of a generational mixed " \
367 "evacuation collection set (comprised of both young and old " \
368 "regions) is also bounded by this parameter. In percents of " \
369 "total (young-generation) heap size.") \
370 range(1,100) \
371 \
372 product(double, ShenandoahEvacWaste, 1.2, EXPERIMENTAL, \
373 "How much waste evacuations produce within the reserved space. " \
374 "Larger values make evacuations more resilient against " \
375 "evacuation conflicts, at expense of evacuating less on each " \
376 "GC cycle. Smaller values increase the risk of evacuation " \
377 "failures, which will trigger stop-the-world Full GC passes.") \
378 range(1.0,100.0) \
379 \
380 product(double, ShenandoahOldEvacWaste, 1.4, EXPERIMENTAL, \
381 "How much waste evacuations produce within the reserved space. " \
382 "Larger values make evacuations more resilient against " \
383 "evacuation conflicts, at expense of evacuating less on each " \
384 "GC cycle. Smaller values increase the risk of evacuation " \
385 "failures, which will trigger stop-the-world Full GC passes.") \
386 range(1.0,100.0) \
387 \
388 product(double, ShenandoahPromoEvacWaste, 1.2, EXPERIMENTAL, \
389 "How much waste promotions produce within the reserved space. " \
390 "Larger values make evacuations more resilient against " \
391 "evacuation conflicts, at expense of promoting less on each " \
392 "GC cycle. Smaller values increase the risk of evacuation " \
393 "failures, which will trigger stop-the-world Full GC passes.") \
394 range(1.0,100.0) \
395 \
396 product(uintx, ShenandoahMaxEvacLABRatio, 0, EXPERIMENTAL, \
397 "Potentially, each running thread maintains a PLAB for " \
398 "evacuating objects into old-gen memory and a GCLAB for " \
399 "evacuating objects into young-gen memory. Each time a thread " \
400 "exhausts its PLAB or GCLAB, a new local buffer is allocated. " \
401 "By default, the new buffer is twice the size of the previous " \
402 "buffer. The sizes are reset to the minimum at the start of " \
403 "each GC pass. This parameter limits the growth of evacuation " \
404 "buffer sizes to its value multiplied by the minimum buffer " \
405 "size. A higher value allows evacuation allocations to be more " \
406 "efficient because less synchronization is required by " \
407 "individual threads. However, a larger value increases the " \
408 "likelihood of evacuation failures, leading to long " \
409 "stop-the-world pauses. This is because a large value " \
410 "allows individual threads to consume large percentages of " \
411 "the total evacuation budget without necessarily effectively " \
412 "filling their local evacuation buffers with evacuated " \
413 "objects. A value of zero means no maximum size is enforced.") \
414 range(0, 1024) \
415 \
416 product(bool, ShenandoahEvacReserveOverflow, true, EXPERIMENTAL, \
417 "Allow evacuations to overflow the reserved space. Enabling it " \
418 "will make evacuations more resilient when evacuation " \
419 "reserve/waste is incorrect, at the risk that application " \
420 "runs out of memory too early.") \
421 \
422 product(uintx, ShenandoahOldEvacRatioPercent, 75, EXPERIMENTAL, \
423 "The maximum proportion of evacuation from old-gen memory, as " \
424 "a percent ratio. The default value 75 denotes that no more " \
425 "than 75% of the collection set evacuation " \
426 "workload may be evacuate to old-gen heap regions. This limits " \
427 "both the promotion of aged regions and the compaction of " \
428 "existing old regions. A value of 75 denotes that the normal " \
429 "young-gen evacuation is increased by up to four fold. " \
430 "A larger value allows quicker promotion and allows" \
431 "a smaller number of mixed evacuations to process " \
432 "the entire list of old-gen collection candidates at the cost " \
433 "of an increased disruption of the normal cadence of young-gen " \
434 "collections. A value of 100 allows a mixed evacuation to " \
435 "focus entirely on old-gen memory, allowing no young-gen " \
436 "regions to be collected, likely resulting in subsequent " \
437 "allocation failures because the allocation pool is not " \
438 "replenished. A value of 0 allows a mixed evacuation to" \
439 "focus entirely on young-gen memory, allowing no old-gen " \
440 "regions to be collected, likely resulting in subsequent " \
441 "promotion failures and triggering of stop-the-world full GC " \
442 "events.") \
443 range(0,100) \
444 \
445 product(uintx, ShenandoahMinYoungPercentage, 20, EXPERIMENTAL, \
446 "The minimum percentage of the heap to use for the young " \
447 "generation. Heuristics will not adjust the young generation " \
448 "to be less than this.") \
449 range(0, 100) \
450 \
451 product(uintx, ShenandoahMaxYoungPercentage, 100, EXPERIMENTAL, \
452 "The maximum percentage of the heap to use for the young " \
453 "generation. Heuristics will not adjust the young generation " \
454 "to be more than this.") \
455 range(0, 100) \
456 \
457 product(bool, ShenandoahPacing, true, EXPERIMENTAL, \
458 "Pace application allocations to give GC chance to start " \
459 "and complete before allocation failure is reached.") \
460 \
461 product(uintx, ShenandoahPacingMaxDelay, 10, EXPERIMENTAL, \
462 "Max delay for pacing application allocations. Larger values " \
463 "provide more resilience against out of memory, at expense at " \
464 "hiding the GC latencies in the allocation path. Time is in " \
465 "milliseconds. Setting it to arbitrarily large value makes " \
466 "GC effectively stall the threads indefinitely instead of going " \
467 "to degenerated or Full GC.") \
468 \
469 product(uintx, ShenandoahPacingIdleSlack, 2, EXPERIMENTAL, \
470 "How much of heap counted as non-taxable allocations during idle "\
471 "phases. Larger value makes the pacing milder when collector is " \
472 "idle, requiring less rendezvous with control thread. Lower " \
473 "value makes the pacing control less responsive to out-of-cycle " \
474 "allocs. In percent of total heap size.") \
475 range(0, 100) \
476 \
477 product(uintx, ShenandoahPacingCycleSlack, 10, EXPERIMENTAL, \
478 "How much of free space to take as non-taxable allocations " \
479 "the GC cycle. Larger value makes the pacing milder at the " \
480 "beginning of the GC cycle. Lower value makes the pacing less " \
481 "uniform during the cycle. In percent of free space.") \
482 range(0, 100) \
483 \
484 product(double, ShenandoahPacingSurcharge, 1.1, EXPERIMENTAL, \
485 "Additional pacing tax surcharge to help unclutter the heap. " \
486 "Larger values makes the pacing more aggressive. Lower values " \
487 "risk GC cycles finish with less memory than were available at " \
488 "the beginning of it.") \
489 range(1.0, 100.0) \
490 \
491 product(uintx, ShenandoahCriticalFreeThreshold, 1, EXPERIMENTAL, \
492 "How much of the heap needs to be free after recovery cycles, " \
493 "either Degenerated or Full GC to be claimed successful. If this "\
494 "much space is not available, next recovery step would be " \
495 "triggered.") \
496 range(0, 100) \
497 \
498 product(bool, ShenandoahDegeneratedGC, true, DIAGNOSTIC, \
499 "Enable Degenerated GC as the graceful degradation step. " \
500 "Disabling this option leads to degradation to Full GC instead. " \
501 "When running in passive mode, this can be toggled to measure " \
502 "either Degenerated GC or Full GC costs.") \
503 \
504 product(uintx, ShenandoahFullGCThreshold, 3, EXPERIMENTAL, \
505 "How many back-to-back Degenerated GCs should happen before " \
506 "going to a Full GC.") \
507 \
508 product(uintx, ShenandoahNoProgressThreshold, 5, EXPERIMENTAL, \
509 "After this number of consecutive Full GCs fail to make " \
510 "progress, Shenandoah will raise out of memory errors. Note " \
511 "that progress is determined by ShenandoahCriticalFreeThreshold") \
512 \
513 product(bool, ShenandoahImplicitGCInvokesConcurrent, false, EXPERIMENTAL, \
514 "Should internally-caused GC requests invoke concurrent cycles, " \
515 "should they do the stop-the-world (Degenerated / Full GC)? " \
516 "Many heuristics automatically enable this. This option is " \
517 "similar to global ExplicitGCInvokesConcurrent.") \
518 \
519 product(bool, ShenandoahHumongousMoves, true, DIAGNOSTIC, \
520 "Allow moving humongous regions. This makes GC more resistant " \
521 "to external fragmentation that may otherwise fail other " \
522 "humongous allocations, at the expense of higher GC copying " \
523 "costs. Currently affects stop-the-world (Full) cycle only.") \
524 \
525 product(bool, ShenandoahOOMDuringEvacALot, false, DIAGNOSTIC, \
526 "Testing: simulate OOM during evacuation.") \
527 \
528 product(bool, ShenandoahAllocFailureALot, false, DIAGNOSTIC, \
529 "Testing: make lots of artificial allocation failures.") \
530 \
531 product(uintx, ShenandoahCoalesceChance, 0, DIAGNOSTIC, \
532 "Testing: Abandon remaining mixed collections with this " \
533 "likelihood. Following each mixed collection, abandon all " \
534 "remaining mixed collection candidate regions with likelihood " \
535 "ShenandoahCoalesceChance. Abandoning a mixed collection will " \
536 "cause the old regions to be made parsable, rather than being " \
537 "evacuated.") \
538 range(0, 100) \
539 \
540 product(intx, ShenandoahMarkScanPrefetch, 32, EXPERIMENTAL, \
541 "How many objects to prefetch ahead when traversing mark bitmaps."\
542 "Set to 0 to disable prefetching.") \
543 range(0, 256) \
544 \
545 product(uintx, ShenandoahMarkLoopStride, 1000, EXPERIMENTAL, \
546 "How many items to process during one marking iteration before " \
547 "checking for cancellation, yielding, etc. Larger values improve "\
548 "marking performance at expense of responsiveness.") \
549 \
550 product(uintx, ShenandoahParallelRegionStride, 1024, EXPERIMENTAL, \
551 "How many regions to process at once during parallel region " \
552 "iteration. Affects heaps with lots of regions.") \
553 \
554 product(size_t, ShenandoahSATBBufferSize, 1 * K, EXPERIMENTAL, \
555 "Number of entries in an SATB log buffer.") \
556 range(1, max_uintx) \
557 \
558 product(uintx, ShenandoahMaxSATBBufferFlushes, 5, EXPERIMENTAL, \
559 "How many times to maximum attempt to flush SATB buffers at the " \
560 "end of concurrent marking.") \
561 \
562 product(bool, ShenandoahSuspendibleWorkers, true, EXPERIMENTAL, \
563 "Suspend concurrent GC worker threads at safepoints") \
564 \
565 product(bool, ShenandoahSATBBarrier, true, DIAGNOSTIC, \
566 "Turn on/off SATB barriers in Shenandoah") \
567 \
568 product(bool, ShenandoahIUBarrier, false, DIAGNOSTIC, \
569 "Turn on/off I-U barriers barriers in Shenandoah") \
570 \
571 product(bool, ShenandoahCardBarrier, false, DIAGNOSTIC, \
572 "Turn on/off card-marking post-write barrier in Shenandoah: " \
573 " true when ShenandoahGCMode is generational, false otherwise") \
574 \
575 product(bool, ShenandoahCASBarrier, true, DIAGNOSTIC, \
576 "Turn on/off CAS barriers in Shenandoah") \
577 \
578 product(bool, ShenandoahCloneBarrier, true, DIAGNOSTIC, \
579 "Turn on/off clone barriers in Shenandoah") \
580 \
581 product(bool, ShenandoahLoadRefBarrier, true, DIAGNOSTIC, \
582 "Turn on/off load-reference barriers in Shenandoah") \
583 \
584 product(bool, ShenandoahStackWatermarkBarrier, true, DIAGNOSTIC, \
585 "Turn on/off stack watermark barriers in Shenandoah") \
586 \
587 develop(bool, ShenandoahVerifyOptoBarriers, false, \
588 "Verify no missing barriers in C2.") \
589 \
590 product(bool, ShenandoahLoopOptsAfterExpansion, true, DIAGNOSTIC, \
591 "Attempt more loop opts after barrier expansion.") \
592 \
593 product(bool, ShenandoahSelfFixing, true, DIAGNOSTIC, \
594 "Fix references with load reference barrier. Disabling this " \
595 "might degrade performance.") \
596 \
597 product(uintx, ShenandoahOldCompactionReserve, 8, EXPERIMENTAL, \
598 "During generational GC, prevent promotions from filling " \
599 "this number of heap regions. These regions are reserved " \
600 "for the purpose of supporting compaction of old-gen " \
601 "memory. Otherwise, old-gen memory cannot be compacted.") \
602 range(0, 128) \
603 \
604 product(bool, ShenandoahAllowOldMarkingPreemption, true, DIAGNOSTIC, \
605 "Allow young generation collections to suspend concurrent" \
606 " marking in the old generation.") \
607 \
608 product(uintx, ShenandoahAgingCyclePeriod, 1, EXPERIMENTAL, \
609 "With generational mode, increment the age of objects and" \
610 "regions each time this many young-gen GC cycles are completed.") \
611 \
612 notproduct(bool, ShenandoahEnableCardStats, false, \
613 "Enable statistics collection related to clean & dirty cards") \
614 \
615 notproduct(int, ShenandoahCardStatsLogInterval, 50, \
616 "Log cumulative card stats every so many remembered set or " \
617 "update refs scans") \
618 // end of GC_SHENANDOAH_FLAGS
619
620 #endif // SHARE_GC_SHENANDOAH_SHENANDOAH_GLOBALS_HPP