1 /* 2 * Copyright (c) 2020, 2023, Oracle and/or its affiliates. All rights reserved. 3 * Copyright (c) 2016, 2021, Red Hat, Inc. All rights reserved. 4 * Copyright Amazon.com Inc. or its affiliates. All Rights Reserved. 5 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. 6 * 7 * This code is free software; you can redistribute it and/or modify it 8 * under the terms of the GNU General Public License version 2 only, as 9 * published by the Free Software Foundation. 10 * 11 * This code is distributed in the hope that it will be useful, but WITHOUT 12 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or 13 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License 14 * version 2 for more details (a copy is included in the LICENSE file that 15 * accompanied this code). 16 * 17 * You should have received a copy of the GNU General Public License version 18 * 2 along with this work; if not, write to the Free Software Foundation, 19 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. 20 * 21 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA 22 * or visit www.oracle.com if you need additional information or have any 23 * questions. 24 * 25 */ 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