1 /*
2 * Copyright (c) 2020, Oracle and/or its affiliates. All rights reserved.
3 * Copyright (c) 2016, 2021, Red Hat, Inc. All rights reserved.
4 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
5 *
6 * This code is free software; you can redistribute it and/or modify it
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25
26 #ifndef SHARE_GC_SHENANDOAH_SHENANDOAH_GLOBALS_HPP
27 #define SHARE_GC_SHENANDOAH_SHENANDOAH_GLOBALS_HPP
28
29 #define GC_SHENANDOAH_FLAGS(develop, \
30 develop_pd, \
31 product, \
32 product_pd, \
33 notproduct, \
34 range, \
35 constraint) \
36 \
37 product(size_t, ShenandoahRegionSize, 0, EXPERIMENTAL, \
38 "Static heap region size. Set zero to enable automatic sizing.") \
39 \
40 product(size_t, ShenandoahTargetNumRegions, 2048, EXPERIMENTAL, \
41 "With automatic region sizing, this is the approximate number " \
42 "of regions that would be used, within min/max region size " \
43 "limits.") \
44 \
45 product(size_t, ShenandoahMinRegionSize, 256 * K, EXPERIMENTAL, \
46 "With automatic region sizing, the regions would be at least " \
47 "this large.") \
48 \
49 product(size_t, ShenandoahMaxRegionSize, 32 * M, EXPERIMENTAL, \
50 "With automatic region sizing, the regions would be at most " \
51 "this large.") \
52 \
53 product(intx, ShenandoahHumongousThreshold, 100, EXPERIMENTAL, \
54 "Humongous objects are allocated in separate regions. " \
55 "This setting defines how large the object should be to be " \
56 "deemed humongous. Value is in percents of heap region size. " \
57 "This also caps the maximum TLAB size.") \
58 range(1, 100) \
59 \
60 product(ccstr, ShenandoahGCMode, "satb", \
61 "GC mode to use. Among other things, this defines which " \
62 "barriers are in in use. Possible values are:" \
63 " satb - snapshot-at-the-beginning concurrent GC (three pass mark-evac-update);" \
64 " iu - incremental-update concurrent GC (three pass mark-evac-update);" \
65 " passive - stop the world GC only (either degenerated or full);" \
66 " generational - generational concurrent GC") \
67 \
68 product(ccstr, ShenandoahGCHeuristics, "adaptive", \
69 "GC heuristics to use. This fine-tunes the GC mode selected, " \
70 "by choosing when to start the GC, how much to process on each " \
71 "cycle, and what other features to automatically enable. " \
72 "Possible values are:" \
73 " adaptive - adapt to maintain the given amount of free heap " \
74 "at all times, even during the GC cycle;" \
75 " static - trigger GC when free heap falls below the threshold;" \
76 " aggressive - run GC continuously, try to evacuate everything;" \
77 " compact - run GC more frequently and with deeper targets to " \
78 "free up more memory.") \
79 \
80 product(ccstr, ShenandoahOldGCHeuristics, "adaptive", \
81 "Similar to ShenandoahGCHeuristics, but applied to the old " \
82 "generation. This configuration is only used to trigger old " \
83 "collections and does not change how regions are selected " \
84 "for collection.") \
85 \
86 product(uintx, ShenandoahUnloadClassesFrequency, 1, EXPERIMENTAL, \
87 "Unload the classes every Nth cycle. Normally affects concurrent "\
88 "GC cycles, as degenerated and full GCs would try to unload " \
89 "classes regardless. Set to zero to disable class unloading.") \
90 \
91 product(uintx, ShenandoahGarbageThreshold, 25, EXPERIMENTAL, \
92 "How much garbage a region has to contain before it would be " \
93 "taken for collection. This a guideline only, as GC heuristics " \
94 "may select the region for collection even if it has little " \
95 "garbage. This also affects how much internal fragmentation the " \
96 "collector accepts. In percents of heap region size.") \
97 range(0,100) \
98 \
99 product(uintx, ShenandoahOldGarbageThreshold, 25, EXPERIMENTAL, \
100 "How much garbage an old region has to contain before it would " \
101 "be taken for collection.") \
102 range(0,100) \
103 \
104 product(uintx, ShenandoahInitFreeThreshold, 70, EXPERIMENTAL, \
105 "When less than this amount of memory is free within the" \
106 "heap or generation, trigger a learning cycle if we are " \
107 "in learning mode. Learning mode happens during initialization " \
108 "and following a drastic state change, such as following a " \
109 "degenerated or Full GC cycle. In percents of soft max " \
110 "heap size.") \
111 range(0,100) \
112 \
113 product(uintx, ShenandoahMinFreeThreshold, 10, EXPERIMENTAL, \
114 "Percentage of free heap memory below which most heuristics " \
115 "trigger collection independent of other triggers. Provides " \
116 "a safety margin for many heuristics. In percents of (soft) " \
117 "max heap size.") \
118 range(0,100) \
119 \
120 product(uintx, ShenandoahAllocationThreshold, 0, EXPERIMENTAL, \
121 "How many new allocations should happen since the last GC cycle " \
122 "before some heuristics trigger the collection. In percents of " \
123 "(soft) max heap size. Set to zero to effectively disable.") \
124 range(0,100) \
125 \
126 product(uintx, ShenandoahAllocSpikeFactor, 5, EXPERIMENTAL, \
127 "How much of heap should some heuristics reserve for absorbing " \
128 "the allocation spikes. Larger value wastes more memory in " \
129 "non-emergency cases, but provides more safety in emergency " \
130 "cases. In percents of (soft) max heap size.") \
131 range(0,100) \
132 \
133 product(uintx, ShenandoahLearningSteps, 5, EXPERIMENTAL, \
134 "The number of cycles some heuristics take to collect in order " \
135 "to learn application and GC performance.") \
136 range(0,100) \
137 \
138 product(uintx, ShenandoahImmediateThreshold, 90, EXPERIMENTAL, \
139 "The cycle may shortcut when enough garbage can be reclaimed " \
140 "from the immediate garbage (completely garbage regions). " \
141 "In percents of total garbage found. Setting this threshold " \
142 "to 100 effectively disables the shortcut.") \
143 range(0,100) \
144 \
145 product(uintx, ShenandoahAdaptiveSampleFrequencyHz, 10, EXPERIMENTAL, \
146 "The number of times per second to update the allocation rate " \
147 "moving average.") \
148 \
149 product(uintx, ShenandoahAdaptiveSampleSizeSeconds, 10, EXPERIMENTAL, \
150 "The size of the moving window over which the average " \
151 "allocation rate is maintained. The total number of samples " \
152 "is the product of this number and the sample frequency.") \
153 \
154 product(double, ShenandoahAdaptiveInitialConfidence, 1.8, EXPERIMENTAL, \
155 "The number of standard deviations used to determine an initial " \
156 "margin of error for the average cycle time and average " \
157 "allocation rate. Increasing this value will cause the " \
158 "heuristic to initiate more concurrent cycles." ) \
159 \
160 product(double, ShenandoahAdaptiveInitialSpikeThreshold, 1.8, EXPERIMENTAL, \
161 "If the most recently sampled allocation rate is more than " \
162 "this many standard deviations away from the moving average, " \
163 "then a cycle is initiated. This value controls how sensitive " \
164 "the heuristic is to allocation spikes. Decreasing this number " \
165 "increases the sensitivity. ") \
166 \
167 product(double, ShenandoahAdaptiveDecayFactor, 0.5, EXPERIMENTAL, \
168 "The decay factor (alpha) used for values in the weighted " \
169 "moving average of cycle time and allocation rate. " \
170 "Larger values give more weight to recent values.") \
171 range(0,1.0) \
172 \
173 product(bool, ShenandoahAdaptiveIgnoreShortCycles, true, EXPERIMENTAL, \
174 "The adaptive heuristic tracks a moving average of cycle " \
175 "times in order to start a gc before memory is exhausted. " \
176 "In some cases, Shenandoah may skip the evacuation and update " \
177 "reference phases, resulting in a shorter cycle. These may skew " \
178 "the average cycle time downward and may cause the heuristic " \
179 "to wait too long to start a cycle. Disabling this will have " \
180 "the gc run less often, which will reduce CPU utilization, but" \
181 "increase the risk of degenerated cycles.") \
182 \
183 product(uintx, ShenandoahGuaranteedGCInterval, 5*60*1000, EXPERIMENTAL, \
184 "Many heuristics would guarantee a concurrent GC cycle at " \
185 "least with this interval. This is useful when large idle " \
186 "intervals are present, where GC can run without stealing " \
187 "time from active application. Time is in milliseconds. " \
188 "Setting this to 0 disables the feature.") \
189 \
190 product(uintx, ShenandoahGuaranteedOldGCInterval, 10*60*1000, EXPERIMENTAL, \
191 "Run a collection of the old generation at least this often. " \
192 "Heuristics may trigger collections more frequently. Time is in " \
193 "milliseconds. Setting this to 0 disables the feature.") \
194 \
195 product(uintx, ShenandoahGuaranteedYoungGCInterval, 5*60*1000, EXPERIMENTAL, \
196 "Run a collection of the young generation at least this often. " \
197 "Heuristics may trigger collections more frequently. Time is in " \
198 "milliseconds. Setting this to 0 disables the feature.") \
199 \
200 product(bool, ShenandoahAlwaysClearSoftRefs, false, EXPERIMENTAL, \
201 "Unconditionally clear soft references, instead of using any " \
202 "other cleanup policy. This minimizes footprint at expense of" \
203 "more soft reference churn in applications.") \
204 \
205 product(bool, ShenandoahUncommit, true, EXPERIMENTAL, \
206 "Allow to uncommit memory under unused regions and metadata. " \
207 "This optimizes footprint at expense of allocation latency in " \
208 "regions that require committing back. Uncommits would be " \
209 "disabled by some heuristics, or with static heap size.") \
210 \
211 product(uintx, ShenandoahUncommitDelay, 5*60*1000, EXPERIMENTAL, \
212 "Uncommit memory for regions that were not used for more than " \
213 "this time. First use after that would incur allocation stalls. " \
214 "Actively used regions would never be uncommitted, because they " \
215 "do not become unused longer than this delay. Time is in " \
216 "milliseconds. Setting this delay to 0 effectively uncommits " \
217 "regions almost immediately after they become unused.") \
218 \
219 product(bool, ShenandoahRegionSampling, false, EXPERIMENTAL, \
220 "Provide heap region sampling data via jvmstat.") \
221 \
222 product(int, ShenandoahRegionSamplingRate, 40, EXPERIMENTAL, \
223 "Sampling rate for heap region sampling. In milliseconds between "\
224 "the samples. Higher values provide more fidelity, at expense " \
225 "of more sampling overhead.") \
226 \
227 product(bool, ShenandoahLogRegionSampling, false, \
228 "Save region sampling stream to ShenandoahRegionSamplingFile") \
229 \
230 product(ccstr, ShenandoahRegionSamplingFile, \
231 "./shenandoahSnapshots_pid%p.log", \
232 "If ShenandoahLogRegionSampling is on, save sampling data stream "\
233 "to this file [default: ./shenandoahSnapshots_pid%p.log] " \
234 "(%p replaced with pid)") \
235 \
236 product(uintx, ShenandoahControlIntervalMin, 1, EXPERIMENTAL, \
237 "The minimum sleep interval for the control loop that drives " \
238 "the cycles. Lower values would increase GC responsiveness " \
239 "to changing heap conditions, at the expense of higher perf " \
240 "overhead. Time is in milliseconds.") \
241 \
242 product(uintx, ShenandoahControlIntervalMax, 10, EXPERIMENTAL, \
243 "The maximum sleep interval for control loop that drives " \
244 "the cycles. Lower values would increase GC responsiveness " \
245 "to changing heap conditions, at the expense of higher perf " \
246 "overhead. Time is in milliseconds.") \
247 \
248 product(uintx, ShenandoahControlIntervalAdjustPeriod, 1000, EXPERIMENTAL, \
249 "The time period for one step in control loop interval " \
250 "adjustment. Lower values make adjustments faster, at the " \
251 "expense of higher perf overhead. Time is in milliseconds.") \
252 \
253 product(bool, ShenandoahVerify, false, DIAGNOSTIC, \
254 "Enable internal verification. This would catch many GC bugs, " \
255 "but it would also stall the collector during the verification, " \
256 "which prolongs the pauses and might hide other bugs.") \
257 \
258 product(intx, ShenandoahVerifyLevel, 4, DIAGNOSTIC, \
259 "Verification level, higher levels check more, taking more time. "\
260 "Accepted values are:" \
261 " 0 = basic heap checks; " \
262 " 1 = previous level, plus basic region checks; " \
263 " 2 = previous level, plus all roots; " \
264 " 3 = previous level, plus all reachable objects; " \
265 " 4 = previous level, plus all marked objects") \
266 \
267 product(bool, ShenandoahElasticTLAB, true, DIAGNOSTIC, \
268 "Use Elastic TLABs with Shenandoah") \
269 \
270 product(bool, ShenandoahUsePLAB, true, DIAGNOSTIC, \
271 "Use PLABs for object promotions with Shenandoah, " \
272 "if in generational mode and UseTLAB is also set.") \
273 \
274 product(uintx, ShenandoahEvacReserve, 5, EXPERIMENTAL, \
275 "How much of (young-generation) heap to reserve for " \
276 "(young-generation) evacuations. Larger values allow GC to " \
277 "evacuate more live objects on every cycle, while leaving " \
278 "less headroom for application to allocate while GC is " \
279 "evacuating and updating references. This parameter is " \
280 "consulted at the of marking, before selecting the collection " \
281 "set. If available memory at this time is smaller than the " \
282 "indicated reserve, the bound on collection set size is " \
283 "adjusted downward. The size of a generational mixed " \
284 "evacuation collection set (comprised of both young and old " \
285 "regions) is also bounded by this parameter. In percents of " \
286 "total (young-generation) heap size.") \
287 range(1,100) \
288 \
289 product(double, ShenandoahEvacWaste, 1.2, EXPERIMENTAL, \
290 "How much waste evacuations produce within the reserved space. " \
291 "Larger values make evacuations more resilient against " \
292 "evacuation conflicts, at expense of evacuating less on each " \
293 "GC cycle. Smaller values increase the risk of evacuation " \
294 "failures, which will trigger stop-the-world Full GC passes.") \
295 range(1.0,100.0) \
296 \
297 product(double, ShenandoahGenerationalEvacWaste, 2.0, EXPERIMENTAL, \
298 "For generational mode, how much waste evacuations produce " \
299 "within the reserved space. Larger values make evacuations " \
300 "more resilient against evacuation conflicts, at expense of " \
301 "evacuating less on each GC cycle. Smaller values increase " \
302 "the risk of evacuation failures, which will trigger " \
303 "stop-the-world Full GC passes. The default value for " \
304 "generational mode is 2.0. The reason for the higher default " \
305 "value in generational mode is because generational mode " \
306 "enforces the evacuation budget, triggering degenerated GC " \
307 "which upgrades to full GC whenever the budget is exceeded.") \
308 range(1.0,100.0) \
309 \
310 product(uintx, ShenandoahMaxEvacLABRatio, 16, EXPERIMENTAL, \
311 "Potentially, each running thread maintains a PLAB for " \
312 "evacuating objects into old-gen memory and a GCLAB for " \
313 "evacuating objects into young-gen memory. Each time a thread " \
314 "exhausts its PLAB or GCLAB, a new local buffer is allocated. " \
315 "By default, the new buffer is twice the size of the previous " \
316 "buffer. The sizes are reset to the minimum at the start of " \
317 "each GC pass. This parameter limits the growth of evacuation " \
318 "buffer sizes to its value multiplied by the minimum buffer " \
319 "size. A higher value allows evacuation allocations to be more " \
320 "efficient because less synchronization is required by " \
321 "individual threads. However, a larger value increases the " \
322 "likelihood of evacuation failures, leading to long " \
323 "stop-the-world pauses. This is because a large value " \
324 "allows individual threads to consume large percentages of " \
325 "the total evacuation budget without necessarily effectively " \
326 "filling their local evcauation buffers with evacuated " \
327 "objects. A value of zero means no maximum size is enforced.") \
328 range(0, 1024) \
329 \
330 product(bool, ShenandoahEvacReserveOverflow, true, EXPERIMENTAL, \
331 "Allow evacuations to overflow the reserved space. Enabling it " \
332 "will make evacuations more resilient when evacuation " \
333 "reserve/waste is incorrect, at the risk that application " \
334 "runs out of memory too early.") \
335 \
336 product(uintx, ShenandoahOldEvacReserve, 2, EXPERIMENTAL, \
337 "How much of old-generation heap to reserve for old-generation " \
338 "evacuations. Larger values allow GC to evacuate more live " \
339 "old-generation objects on every cycle, while potentially " \
340 "creating greater impact on the cadence at which the young- " \
341 "generation allocation pool is replenished. During mixed " \
342 "evacuations, the bound on amount of old-generation heap " \
343 "regions included in the collecdtion set is the smaller " \
344 "of the quantities specified by this parameter and the " \
345 "size of ShenandoahEvacReserve as adjusted by the value of " \
346 "ShenandoahOldEvacRatioPercent. In percents of total " \
347 "old-generation heap size.") \
348 range(1,100) \
349 \
350 product(uintx, ShenandoahOldEvacRatioPercent, 12, EXPERIMENTAL, \
351 "The maximum proportion of evacuation from old-gen memory, as " \
352 "a percent ratio. The default value 12 denotes that no more " \
353 "than one eighth (12%) of the collection set evacuation " \
354 "workload may be comprised of old-gen heap regions. A larger " \
355 "value allows a smaller number of mixed evacuations to process " \
356 "the entire list of old-gen collection candidates at the cost " \
357 "of an increased disruption of the normal cadence of young-gen " \
358 "collections. A value of 100 allows a mixed evacuation to " \
359 "focus entirely on old-gen memory, allowing no young-gen " \
360 "regions to be collected, likely resulting in subsequent " \
361 "allocation failures because the allocation pool is not " \
362 "replenished. A value of 0 allows a mixed evacuation to" \
363 "focus entirely on young-gen memory, allowing no old-gen " \
364 "regions to be collected, likely resulting in subsequent " \
365 "promotion failures and triggering of stop-the-world full GC " \
366 "events.") \
367 range(0,100) \
368 \
369 product(bool, ShenandoahPacing, true, EXPERIMENTAL, \
370 "Pace application allocations to give GC chance to start " \
371 "and complete before allocation failure is reached.") \
372 \
373 product(uintx, ShenandoahPacingMaxDelay, 10, EXPERIMENTAL, \
374 "Max delay for pacing application allocations. Larger values " \
375 "provide more resilience against out of memory, at expense at " \
376 "hiding the GC latencies in the allocation path. Time is in " \
377 "milliseconds. Setting it to arbitrarily large value makes " \
378 "GC effectively stall the threads indefinitely instead of going " \
379 "to degenerated or Full GC.") \
380 \
381 product(uintx, ShenandoahPacingIdleSlack, 2, EXPERIMENTAL, \
382 "How much of heap counted as non-taxable allocations during idle "\
383 "phases. Larger value makes the pacing milder when collector is " \
384 "idle, requiring less rendezvous with control thread. Lower " \
385 "value makes the pacing control less responsive to out-of-cycle " \
386 "allocs. In percent of total heap size.") \
387 range(0, 100) \
388 \
389 product(uintx, ShenandoahPacingCycleSlack, 10, EXPERIMENTAL, \
390 "How much of free space to take as non-taxable allocations " \
391 "the GC cycle. Larger value makes the pacing milder at the " \
392 "beginning of the GC cycle. Lower value makes the pacing less " \
393 "uniform during the cycle. In percent of free space.") \
394 range(0, 100) \
395 \
396 product(double, ShenandoahPacingSurcharge, 1.1, EXPERIMENTAL, \
397 "Additional pacing tax surcharge to help unclutter the heap. " \
398 "Larger values makes the pacing more aggressive. Lower values " \
399 "risk GC cycles finish with less memory than were available at " \
400 "the beginning of it.") \
401 range(1.0, 100.0) \
402 \
403 product(uintx, ShenandoahCriticalFreeThreshold, 1, EXPERIMENTAL, \
404 "How much of the heap needs to be free after recovery cycles, " \
405 "either Degenerated or Full GC to be claimed successful. If this "\
406 "much space is not available, next recovery step would be " \
407 "triggered.") \
408 range(0, 100) \
409 \
410 product(bool, ShenandoahDegeneratedGC, true, DIAGNOSTIC, \
411 "Enable Degenerated GC as the graceful degradation step. " \
412 "Disabling this option leads to degradation to Full GC instead. " \
413 "When running in passive mode, this can be toggled to measure " \
414 "either Degenerated GC or Full GC costs.") \
415 \
416 product(uintx, ShenandoahFullGCThreshold, 3, EXPERIMENTAL, \
417 "How many back-to-back Degenerated GCs should happen before " \
418 "going to a Full GC.") \
419 \
420 product(bool, ShenandoahImplicitGCInvokesConcurrent, false, EXPERIMENTAL, \
421 "Should internally-caused GC requests invoke concurrent cycles, " \
422 "should they do the stop-the-world (Degenerated / Full GC)? " \
423 "Many heuristics automatically enable this. This option is " \
424 "similar to global ExplicitGCInvokesConcurrent.") \
425 \
426 product(bool, ShenandoahHumongousMoves, true, DIAGNOSTIC, \
427 "Allow moving humongous regions. This makes GC more resistant " \
428 "to external fragmentation that may otherwise fail other " \
429 "humongous allocations, at the expense of higher GC copying " \
430 "costs. Currently affects stop-the-world (Full) cycle only.") \
431 \
432 product(bool, ShenandoahOOMDuringEvacALot, false, DIAGNOSTIC, \
433 "Testing: simulate OOM during evacuation.") \
434 \
435 product(bool, ShenandoahAllocFailureALot, false, DIAGNOSTIC, \
436 "Testing: make lots of artificial allocation failures.") \
437 \
438 product(intx, ShenandoahMarkScanPrefetch, 32, EXPERIMENTAL, \
439 "How many objects to prefetch ahead when traversing mark bitmaps."\
440 "Set to 0 to disable prefetching.") \
441 range(0, 256) \
442 \
443 product(uintx, ShenandoahMarkLoopStride, 1000, EXPERIMENTAL, \
444 "How many items to process during one marking iteration before " \
445 "checking for cancellation, yielding, etc. Larger values improve "\
446 "marking performance at expense of responsiveness.") \
447 \
448 product(uintx, ShenandoahParallelRegionStride, 1024, EXPERIMENTAL, \
449 "How many regions to process at once during parallel region " \
450 "iteration. Affects heaps with lots of regions.") \
451 \
452 product(size_t, ShenandoahSATBBufferSize, 1 * K, EXPERIMENTAL, \
453 "Number of entries in an SATB log buffer.") \
454 range(1, max_uintx) \
455 \
456 product(uintx, ShenandoahMaxSATBBufferFlushes, 5, EXPERIMENTAL, \
457 "How many times to maximum attempt to flush SATB buffers at the " \
458 "end of concurrent marking.") \
459 \
460 product(bool, ShenandoahSuspendibleWorkers, false, EXPERIMENTAL, \
461 "Suspend concurrent GC worker threads at safepoints") \
462 \
463 product(bool, ShenandoahSATBBarrier, true, DIAGNOSTIC, \
464 "Turn on/off SATB barriers in Shenandoah") \
465 \
466 product(bool, ShenandoahIUBarrier, false, DIAGNOSTIC, \
467 "Turn on/off I-U barriers barriers in Shenandoah") \
468 \
469 product(bool, ShenandoahCASBarrier, true, DIAGNOSTIC, \
470 "Turn on/off CAS barriers in Shenandoah") \
471 \
472 product(bool, ShenandoahCloneBarrier, true, DIAGNOSTIC, \
473 "Turn on/off clone barriers in Shenandoah") \
474 \
475 product(bool, ShenandoahLoadRefBarrier, true, DIAGNOSTIC, \
476 "Turn on/off load-reference barriers in Shenandoah") \
477 \
478 product(bool, ShenandoahNMethodBarrier, true, DIAGNOSTIC, \
479 "Turn on/off NMethod entry barriers in Shenandoah") \
480 \
481 product(bool, ShenandoahStackWatermarkBarrier, true, DIAGNOSTIC, \
482 "Turn on/off stack watermark barriers in Shenandoah") \
483 \
484 develop(bool, ShenandoahVerifyOptoBarriers, false, \
485 "Verify no missing barriers in C2.") \
486 \
487 product(bool, ShenandoahLoopOptsAfterExpansion, true, DIAGNOSTIC, \
488 "Attempt more loop opts after barrier expansion.") \
489 \
490 product(bool, ShenandoahSelfFixing, true, DIAGNOSTIC, \
491 "Fix references with load reference barrier. Disabling this " \
492 "might degrade performance.") \
493 \
494 product(uintx, ShenandoahTenuredRegionUsageBias, 16, EXPERIMENTAL, \
495 "The collection set is comprised of heap regions that contain " \
496 "the greatest amount of garbage. " \
497 "For purposes of selecting regions to be included in the " \
498 "collection set, regions that have reached the tenure age will " \
499 "be treated as if their contained garbage is the contained " \
500 "garbage multiplied by ShenandoahTenuredRegionUsageBias as " \
501 "many times as the age of the region meets or exceeds " \
502 "tenure age. For example, if tenure age is 7, " \
503 "the region age is 9, ShenandoahTenuredRegionUsageBias is " \
504 "16, and the region is 12.5% garbage, this region " \
505 "will by treated as if its garbage content is " \
506 "12.5% * 16 * 16 * 16 = 51,200% when comparing this region " \
507 " to untenured regions.") \
508 range(1,128) \
509 \
510 product(uintx, ShenandoahBorrowPercent, 30, EXPERIMENTAL, \
511 "During evacuation and reference updating in generational " \
512 "mode, new allocations are allowed to borrow from old-gen " \
513 "memory up to ShenandoahBorrowPercent / 100 amount of the " \
514 "young-generation content of the current collection set. " \
515 "Any memory borrowed from old-gen during evacuation and " \
516 "update-references phases of GC will be repaid from the " \
517 "abundance of young-gen memory produced when the collection " \
518 "set is recycled at the end of updating references. The " \
519 "default value of 30 reserves 70% of the to-be-reclaimed " \
520 "young collection set memory to be allocated during the " \
521 "subsequent concurrent mark phase of GC.") \
522 range(0, 100) \
523 \
524 product(bool, ShenandoahPromoteTenuredObjects, true, DIAGNOSTIC, \
525 "Turn on/off evacuating individual tenured young objects " \
526 " to the old generation.") \
527 \
528 product(bool, ShenandoahAllowOldMarkingPreemption, true, DIAGNOSTIC, \
529 "Allow young generation collections to suspend concurrent" \
530 " marking in the old generation.") \
531 \
532 product(uintx, ShenandoahAgingCyclePeriod, 1, EXPERIMENTAL, \
533 "With generational mode, increment the age of objects and" \
534 "regions each time this many young-gen GC cycles are completed.")
535 // end of GC_SHENANDOAH_FLAGS
536
537 #endif // SHARE_GC_SHENANDOAH_SHENANDOAH_GLOBALS_HPP