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.
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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, ShenandoahIgnoreGarbageThreshold, 5, EXPERIMENTAL, \
105 "When less than this amount of garbage (as a percentage of " \
106 "region size) exists within a region, the region will not be " \
107 "added to the collection set, even when the heuristic has " \
108 "chosen to aggressively add regions with less than " \
109 "ShenandoahGarbageThreshold amount of garbage into the " \
110 "collection set.") \
111 range(0,100) \
112 \
113 product(uintx, ShenandoahInitFreeThreshold, 70, EXPERIMENTAL, \
114 "When less than this amount of memory is free within the" \
115 "heap or generation, trigger a learning cycle if we are " \
116 "in learning mode. Learning mode happens during initialization " \
117 "and following a drastic state change, such as following a " \
118 "degenerated or Full GC cycle. In percents of soft max " \
119 "heap size.") \
120 range(0,100) \
121 \
122 product(uintx, ShenandoahMinFreeThreshold, 10, EXPERIMENTAL, \
123 "Percentage of free heap memory (or young generation, in " \
124 "generational mode) below which most heuristics trigger " \
125 "collection independent of other triggers. Provides a safety " \
126 "margin for many heuristics. In percents of (soft) max heap " \
127 "size.") \
128 range(0,100) \
129 \
130 product(uintx, ShenandoahOldMinFreeThreshold, 5, EXPERIMENTAL, \
131 "Percentage of free old generation heap memory below which most " \
132 "heuristics trigger collection independent of other triggers. " \
133 "Provides a safety margin for many heuristics. In percents of " \
134 "(soft) max heap size.") \
135 range(0,100) \
136 \
137 product(uintx, ShenandoahAllocationThreshold, 0, EXPERIMENTAL, \
138 "How many new allocations should happen since the last GC cycle " \
139 "before some heuristics trigger the collection. In percents of " \
140 "(soft) max heap size. Set to zero to effectively disable.") \
141 range(0,100) \
142 \
143 product(uintx, ShenandoahAllocSpikeFactor, 5, EXPERIMENTAL, \
144 "How much of heap should some heuristics reserve for absorbing " \
145 "the allocation spikes. Larger value wastes more memory in " \
146 "non-emergency cases, but provides more safety in emergency " \
147 "cases. In percents of (soft) max heap size.") \
148 range(0,100) \
149 \
150 product(uintx, ShenandoahLearningSteps, 5, EXPERIMENTAL, \
151 "The number of cycles some heuristics take to collect in order " \
152 "to learn application and GC performance.") \
153 range(0,100) \
154 \
155 product(uintx, ShenandoahImmediateThreshold, 90, EXPERIMENTAL, \
156 "The cycle may shortcut when enough garbage can be reclaimed " \
157 "from the immediate garbage (completely garbage regions). " \
158 "In percents of total garbage found. Setting this threshold " \
159 "to 100 effectively disables the shortcut.") \
160 range(0,100) \
161 \
162 product(uintx, ShenandoahAdaptiveSampleFrequencyHz, 10, EXPERIMENTAL, \
163 "The number of times per second to update the allocation rate " \
164 "moving average.") \
165 \
166 product(uintx, ShenandoahAdaptiveSampleSizeSeconds, 10, EXPERIMENTAL, \
167 "The size of the moving window over which the average " \
168 "allocation rate is maintained. The total number of samples " \
169 "is the product of this number and the sample frequency.") \
170 \
171 product(double, ShenandoahAdaptiveInitialConfidence, 1.8, EXPERIMENTAL, \
172 "The number of standard deviations used to determine an initial " \
173 "margin of error for the average cycle time and average " \
174 "allocation rate. Increasing this value will cause the " \
175 "heuristic to initiate more concurrent cycles." ) \
176 \
177 product(double, ShenandoahAdaptiveInitialSpikeThreshold, 1.8, EXPERIMENTAL, \
178 "If the most recently sampled allocation rate is more than " \
179 "this many standard deviations away from the moving average, " \
180 "then a cycle is initiated. This value controls how sensitive " \
181 "the heuristic is to allocation spikes. Decreasing this number " \
182 "increases the sensitivity. ") \
183 \
184 product(double, ShenandoahAdaptiveDecayFactor, 0.5, EXPERIMENTAL, \
185 "The decay factor (alpha) used for values in the weighted " \
186 "moving average of cycle time and allocation rate. " \
187 "Larger values give more weight to recent values.") \
188 range(0,1.0) \
189 \
190 product(bool, ShenandoahAdaptiveIgnoreShortCycles, true, EXPERIMENTAL, \
191 "The adaptive heuristic tracks a moving average of cycle " \
192 "times in order to start a gc before memory is exhausted. " \
193 "In some cases, Shenandoah may skip the evacuation and update " \
194 "reference phases, resulting in a shorter cycle. These may skew " \
195 "the average cycle time downward and may cause the heuristic " \
196 "to wait too long to start a cycle. Disabling this will have " \
197 "the gc run less often, which will reduce CPU utilization, but" \
198 "increase the risk of degenerated cycles.") \
199 \
200 product(uintx, ShenandoahGuaranteedGCInterval, 5*60*1000, EXPERIMENTAL, \
201 "Many heuristics would guarantee a concurrent GC cycle at " \
202 "least with this interval. This is useful when large idle " \
203 "intervals are present, where GC can run without stealing " \
204 "time from active application. Time is in milliseconds. " \
205 "Setting this to 0 disables the feature.") \
206 \
207 product(uintx, ShenandoahGuaranteedOldGCInterval, 10*60*1000, EXPERIMENTAL, \
208 "Run a collection of the old generation at least this often. " \
209 "Heuristics may trigger collections more frequently. Time is in " \
210 "milliseconds. Setting this to 0 disables the feature.") \
211 \
212 product(uintx, ShenandoahGuaranteedYoungGCInterval, 5*60*1000, EXPERIMENTAL, \
213 "Run a collection of the young generation at least this often. " \
214 "Heuristics may trigger collections more frequently. Time is in " \
215 "milliseconds. Setting this to 0 disables the feature.") \
216 \
217 product(bool, ShenandoahAlwaysClearSoftRefs, false, EXPERIMENTAL, \
218 "Unconditionally clear soft references, instead of using any " \
219 "other cleanup policy. This minimizes footprint at expense of" \
220 "more soft reference churn in applications.") \
221 \
222 product(bool, ShenandoahUncommit, true, EXPERIMENTAL, \
223 "Allow to uncommit memory under unused regions and metadata. " \
224 "This optimizes footprint at expense of allocation latency in " \
225 "regions that require committing back. Uncommits would be " \
226 "disabled by some heuristics, or with static heap size.") \
227 \
228 product(uintx, ShenandoahUncommitDelay, 5*60*1000, EXPERIMENTAL, \
229 "Uncommit memory for regions that were not used for more than " \
230 "this time. First use after that would incur allocation stalls. " \
231 "Actively used regions would never be uncommitted, because they " \
232 "do not become unused longer than this delay. Time is in " \
233 "milliseconds. Setting this delay to 0 effectively uncommits " \
234 "regions almost immediately after they become unused.") \
235 \
236 product(bool, ShenandoahRegionSampling, false, EXPERIMENTAL, \
237 "Provide heap region sampling data via jvmstat.") \
238 \
239 product(int, ShenandoahRegionSamplingRate, 40, EXPERIMENTAL, \
240 "Sampling rate for heap region sampling. In milliseconds between "\
241 "the samples. Higher values provide more fidelity, at expense " \
242 "of more sampling overhead.") \
243 \
244 product(ccstr, ShenandoahRegionSamplingFile, \
245 "./shenandoahSnapshots_pid%p.log", \
246 "If ShenandoahLogRegionSampling is on, save sampling data stream "\
247 "to this file [default: ./shenandoahSnapshots_pid%p.log] " \
248 "(%p replaced with pid)") \
249 \
250 product(uintx, ShenandoahControlIntervalMin, 1, EXPERIMENTAL, \
251 "The minimum sleep interval for the control loop that drives " \
252 "the cycles. Lower values would increase GC responsiveness " \
253 "to changing heap conditions, at the expense of higher perf " \
254 "overhead. Time is in milliseconds.") \
255 \
256 product(uintx, ShenandoahControlIntervalMax, 10, EXPERIMENTAL, \
257 "The maximum sleep interval for control loop that drives " \
258 "the cycles. Lower values would increase GC responsiveness " \
259 "to changing heap conditions, at the expense of higher perf " \
260 "overhead. Time is in milliseconds.") \
261 \
262 product(uintx, ShenandoahControlIntervalAdjustPeriod, 1000, EXPERIMENTAL, \
263 "The time period for one step in control loop interval " \
264 "adjustment. Lower values make adjustments faster, at the " \
265 "expense of higher perf overhead. Time is in milliseconds.") \
266 \
267 product(bool, ShenandoahVerify, false, DIAGNOSTIC, \
268 "Enable internal verification. This would catch many GC bugs, " \
269 "but it would also stall the collector during the verification, " \
270 "which prolongs the pauses and might hide other bugs.") \
271 \
272 product(intx, ShenandoahVerifyLevel, 4, DIAGNOSTIC, \
273 "Verification level, higher levels check more, taking more time. "\
274 "Accepted values are:" \
275 " 0 = basic heap checks; " \
276 " 1 = previous level, plus basic region checks; " \
277 " 2 = previous level, plus all roots; " \
278 " 3 = previous level, plus all reachable objects; " \
279 " 4 = previous level, plus all marked objects") \
280 \
281 product(bool, ShenandoahElasticTLAB, true, DIAGNOSTIC, \
282 "Use Elastic TLABs with Shenandoah") \
283 \
284 product(bool, ShenandoahUsePLAB, true, DIAGNOSTIC, \
285 "Use PLABs for object promotions with Shenandoah, " \
286 "if in generational mode and UseTLAB is also set.") \
287 \
288 product(uintx, ShenandoahEvacReserve, 5, EXPERIMENTAL, \
289 "How much of (young-generation) heap to reserve for " \
290 "(young-generation) evacuations. Larger values allow GC to " \
291 "evacuate more live objects on every cycle, while leaving " \
292 "less headroom for application to allocate while GC is " \
293 "evacuating and updating references. This parameter is " \
294 "consulted at the of marking, before selecting the collection " \
295 "set. If available memory at this time is smaller than the " \
296 "indicated reserve, the bound on collection set size is " \
297 "adjusted downward. The size of a generational mixed " \
298 "evacuation collection set (comprised of both young and old " \
299 "regions) is also bounded by this parameter. In percents of " \
300 "total (young-generation) heap size.") \
301 range(1,100) \
302 \
303 product(double, ShenandoahEvacWaste, 1.2, EXPERIMENTAL, \
304 "How much waste evacuations produce within the reserved space. " \
305 "Larger values make evacuations more resilient against " \
306 "evacuation conflicts, at expense of evacuating less on each " \
307 "GC cycle. Smaller values increase the risk of evacuation " \
308 "failures, which will trigger stop-the-world Full GC passes.") \
309 range(1.0,100.0) \
310 \
311 product(double, ShenandoahGenerationalEvacWaste, 2.0, EXPERIMENTAL, \
312 "For generational mode, how much waste evacuations produce " \
313 "within the reserved space. Larger values make evacuations " \
314 "more resilient against evacuation conflicts, at expense of " \
315 "evacuating less on each GC cycle. Smaller values increase " \
316 "the risk of evacuation failures, which will trigger " \
317 "stop-the-world Full GC passes. The default value for " \
318 "generational mode is 2.0. The reason for the higher default " \
319 "value in generational mode is because generational mode " \
320 "enforces the evacuation budget, triggering degenerated GC " \
321 "which upgrades to full GC whenever the budget is exceeded.") \
322 range(1.0,100.0) \
323 \
324 product(uintx, ShenandoahMaxEvacLABRatio, 16, EXPERIMENTAL, \
325 "Potentially, each running thread maintains a PLAB for " \
326 "evacuating objects into old-gen memory and a GCLAB for " \
327 "evacuating objects into young-gen memory. Each time a thread " \
328 "exhausts its PLAB or GCLAB, a new local buffer is allocated. " \
329 "By default, the new buffer is twice the size of the previous " \
330 "buffer. The sizes are reset to the minimum at the start of " \
331 "each GC pass. This parameter limits the growth of evacuation " \
332 "buffer sizes to its value multiplied by the minimum buffer " \
333 "size. A higher value allows evacuation allocations to be more " \
334 "efficient because less synchronization is required by " \
335 "individual threads. However, a larger value increases the " \
336 "likelihood of evacuation failures, leading to long " \
337 "stop-the-world pauses. This is because a large value " \
338 "allows individual threads to consume large percentages of " \
339 "the total evacuation budget without necessarily effectively " \
340 "filling their local evcauation buffers with evacuated " \
341 "objects. A value of zero means no maximum size is enforced.") \
342 range(0, 1024) \
343 \
344 product(bool, ShenandoahEvacReserveOverflow, true, EXPERIMENTAL, \
345 "Allow evacuations to overflow the reserved space. Enabling it " \
346 "will make evacuations more resilient when evacuation " \
347 "reserve/waste is incorrect, at the risk that application " \
348 "runs out of memory too early.") \
349 \
350 product(uintx, ShenandoahOldEvacReserve, 2, EXPERIMENTAL, \
351 "How much of old-generation heap to reserve for old-generation " \
352 "evacuations. Larger values allow GC to evacuate more live " \
353 "old-generation objects on every cycle, while potentially " \
354 "creating greater impact on the cadence at which the young- " \
355 "generation allocation pool is replenished. During mixed " \
356 "evacuations, the bound on amount of old-generation heap " \
357 "regions included in the collecdtion set is the smaller " \
358 "of the quantities specified by this parameter and the " \
359 "size of ShenandoahEvacReserve as adjusted by the value of " \
360 "ShenandoahOldEvacRatioPercent. In percents of total " \
361 "old-generation heap size.") \
362 range(1,100) \
363 \
364 product(uintx, ShenandoahOldEvacRatioPercent, 12, EXPERIMENTAL, \
365 "The maximum proportion of evacuation from old-gen memory, as " \
366 "a percent ratio. The default value 12 denotes that no more " \
367 "than one eighth (12%) of the collection set evacuation " \
368 "workload may be comprised of old-gen heap regions. A larger " \
369 "value allows a smaller number of mixed evacuations to process " \
370 "the entire list of old-gen collection candidates at the cost " \
371 "of an increased disruption of the normal cadence of young-gen " \
372 "collections. A value of 100 allows a mixed evacuation to " \
373 "focus entirely on old-gen memory, allowing no young-gen " \
374 "regions to be collected, likely resulting in subsequent " \
375 "allocation failures because the allocation pool is not " \
376 "replenished. A value of 0 allows a mixed evacuation to" \
377 "focus entirely on young-gen memory, allowing no old-gen " \
378 "regions to be collected, likely resulting in subsequent " \
379 "promotion failures and triggering of stop-the-world full GC " \
380 "events.") \
381 range(0,100) \
382 \
383 product(bool, ShenandoahPacing, true, EXPERIMENTAL, \
384 "Pace application allocations to give GC chance to start " \
385 "and complete before allocation failure is reached.") \
386 \
387 product(uintx, ShenandoahPacingMaxDelay, 10, EXPERIMENTAL, \
388 "Max delay for pacing application allocations. Larger values " \
389 "provide more resilience against out of memory, at expense at " \
390 "hiding the GC latencies in the allocation path. Time is in " \
391 "milliseconds. Setting it to arbitrarily large value makes " \
392 "GC effectively stall the threads indefinitely instead of going " \
393 "to degenerated or Full GC.") \
394 \
395 product(uintx, ShenandoahPacingIdleSlack, 2, EXPERIMENTAL, \
396 "How much of heap counted as non-taxable allocations during idle "\
397 "phases. Larger value makes the pacing milder when collector is " \
398 "idle, requiring less rendezvous with control thread. Lower " \
399 "value makes the pacing control less responsive to out-of-cycle " \
400 "allocs. In percent of total heap size.") \
401 range(0, 100) \
402 \
403 product(uintx, ShenandoahPacingCycleSlack, 10, EXPERIMENTAL, \
404 "How much of free space to take as non-taxable allocations " \
405 "the GC cycle. Larger value makes the pacing milder at the " \
406 "beginning of the GC cycle. Lower value makes the pacing less " \
407 "uniform during the cycle. In percent of free space.") \
408 range(0, 100) \
409 \
410 product(double, ShenandoahPacingSurcharge, 1.1, EXPERIMENTAL, \
411 "Additional pacing tax surcharge to help unclutter the heap. " \
412 "Larger values makes the pacing more aggressive. Lower values " \
413 "risk GC cycles finish with less memory than were available at " \
414 "the beginning of it.") \
415 range(1.0, 100.0) \
416 \
417 product(uintx, ShenandoahCriticalFreeThreshold, 1, EXPERIMENTAL, \
418 "How much of the heap needs to be free after recovery cycles, " \
419 "either Degenerated or Full GC to be claimed successful. If this "\
420 "much space is not available, next recovery step would be " \
421 "triggered.") \
422 range(0, 100) \
423 \
424 product(bool, ShenandoahDegeneratedGC, true, DIAGNOSTIC, \
425 "Enable Degenerated GC as the graceful degradation step. " \
426 "Disabling this option leads to degradation to Full GC instead. " \
427 "When running in passive mode, this can be toggled to measure " \
428 "either Degenerated GC or Full GC costs.") \
429 \
430 product(uintx, ShenandoahFullGCThreshold, 3, EXPERIMENTAL, \
431 "How many back-to-back Degenerated GCs should happen before " \
432 "going to a Full GC.") \
433 \
434 product(bool, ShenandoahImplicitGCInvokesConcurrent, false, EXPERIMENTAL, \
435 "Should internally-caused GC requests invoke concurrent cycles, " \
436 "should they do the stop-the-world (Degenerated / Full GC)? " \
437 "Many heuristics automatically enable this. This option is " \
438 "similar to global ExplicitGCInvokesConcurrent.") \
439 \
440 product(bool, ShenandoahHumongousMoves, true, DIAGNOSTIC, \
441 "Allow moving humongous regions. This makes GC more resistant " \
442 "to external fragmentation that may otherwise fail other " \
443 "humongous allocations, at the expense of higher GC copying " \
444 "costs. Currently affects stop-the-world (Full) cycle only.") \
445 \
446 product(bool, ShenandoahOOMDuringEvacALot, false, DIAGNOSTIC, \
447 "Testing: simulate OOM during evacuation.") \
448 \
449 product(bool, ShenandoahAllocFailureALot, false, DIAGNOSTIC, \
450 "Testing: make lots of artificial allocation failures.") \
451 \
452 product(intx, ShenandoahMarkScanPrefetch, 32, EXPERIMENTAL, \
453 "How many objects to prefetch ahead when traversing mark bitmaps."\
454 "Set to 0 to disable prefetching.") \
455 range(0, 256) \
456 \
457 product(uintx, ShenandoahMarkLoopStride, 1000, EXPERIMENTAL, \
458 "How many items to process during one marking iteration before " \
459 "checking for cancellation, yielding, etc. Larger values improve "\
460 "marking performance at expense of responsiveness.") \
461 \
462 product(uintx, ShenandoahParallelRegionStride, 1024, EXPERIMENTAL, \
463 "How many regions to process at once during parallel region " \
464 "iteration. Affects heaps with lots of regions.") \
465 \
466 product(size_t, ShenandoahSATBBufferSize, 1 * K, EXPERIMENTAL, \
467 "Number of entries in an SATB log buffer.") \
468 range(1, max_uintx) \
469 \
470 product(uintx, ShenandoahMaxSATBBufferFlushes, 5, EXPERIMENTAL, \
471 "How many times to maximum attempt to flush SATB buffers at the " \
472 "end of concurrent marking.") \
473 \
474 product(bool, ShenandoahSuspendibleWorkers, false, EXPERIMENTAL, \
475 "Suspend concurrent GC worker threads at safepoints") \
476 \
477 product(bool, ShenandoahSATBBarrier, true, DIAGNOSTIC, \
478 "Turn on/off SATB barriers in Shenandoah") \
479 \
480 product(bool, ShenandoahIUBarrier, false, DIAGNOSTIC, \
481 "Turn on/off I-U barriers barriers in Shenandoah") \
482 \
483 product(bool, ShenandoahCASBarrier, true, DIAGNOSTIC, \
484 "Turn on/off CAS barriers in Shenandoah") \
485 \
486 product(bool, ShenandoahCloneBarrier, true, DIAGNOSTIC, \
487 "Turn on/off clone barriers in Shenandoah") \
488 \
489 product(bool, ShenandoahLoadRefBarrier, true, DIAGNOSTIC, \
490 "Turn on/off load-reference barriers in Shenandoah") \
491 \
492 product(bool, ShenandoahNMethodBarrier, true, DIAGNOSTIC, \
493 "Turn on/off NMethod entry barriers in Shenandoah") \
494 \
495 product(bool, ShenandoahStackWatermarkBarrier, true, DIAGNOSTIC, \
496 "Turn on/off stack watermark barriers in Shenandoah") \
497 \
498 develop(bool, ShenandoahVerifyOptoBarriers, false, \
499 "Verify no missing barriers in C2.") \
500 \
501 product(bool, ShenandoahLoopOptsAfterExpansion, true, DIAGNOSTIC, \
502 "Attempt more loop opts after barrier expansion.") \
503 \
504 product(bool, ShenandoahSelfFixing, true, DIAGNOSTIC, \
505 "Fix references with load reference barrier. Disabling this " \
506 "might degrade performance.") \
507 \
508 product(uintx, ShenandoahBorrowPercent, 30, EXPERIMENTAL, \
509 "During evacuation and reference updating in generational " \
510 "mode, new allocations are allowed to borrow from old-gen " \
511 "memory up to ShenandoahBorrowPercent / 100 amount of the " \
512 "young-generation content of the current collection set. " \
513 "Any memory borrowed from old-gen during evacuation and " \
514 "update-references phases of GC will be repaid from the " \
515 "abundance of young-gen memory produced when the collection " \
516 "set is recycled at the end of updating references. The " \
517 "default value of 30 reserves 70% of the to-be-reclaimed " \
518 "young collection set memory to be allocated during the " \
519 "subsequent concurrent mark phase of GC.") \
520 range(0, 100) \
521 \
522 product(uintx, ShenandoahOldCompactionReserve, 8, EXPERIMENTAL, \
523 "During generational GC, prevent promotions from filling " \
524 "this number of heap regions. These regions are reserved " \
525 "for the purpose of supporting compaction of old-gen " \
526 "memory. Otherwise, old-gen memory cannot be compacted.") \
527 range(0, 128) \
528 \
529 product(bool, ShenandoahPromoteTenuredObjects, true, DIAGNOSTIC, \
530 "Turn on/off evacuating individual tenured young objects " \
531 " to the old generation.") \
532 \
533 product(bool, ShenandoahAllowOldMarkingPreemption, true, DIAGNOSTIC, \
534 "Allow young generation collections to suspend concurrent" \
535 " marking in the old generation.") \
536 \
537 product(uintx, ShenandoahAgingCyclePeriod, 1, EXPERIMENTAL, \
538 "With generational mode, increment the age of objects and" \
539 "regions each time this many young-gen GC cycles are completed.")
540 // end of GC_SHENANDOAH_FLAGS
541
542 #endif // SHARE_GC_SHENANDOAH_SHENANDOAH_GLOBALS_HPP