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 7 * under the terms of the GNU General Public License version 2 only, as 8 * published by the Free Software Foundation. 9 * 10 * This code is distributed in the hope that it will be useful, but WITHOUT 11 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or 12 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License 13 * version 2 for more details (a copy is included in the LICENSE file that 14 * accompanied this code). 15 * 16 * You should have received a copy of the GNU General Public License version 17 * 2 along with this work; if not, write to the Free Software Foundation, 18 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. 19 * 20 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA 21 * or visit www.oracle.com if you need additional information or have any 22 * questions. 23 * 24 */ 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