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(size_t, ShenandoahRegionSize, 0, EXPERIMENTAL, \ 39 "Static heap region size. Set zero to enable automatic sizing.") \ 40 \ 41 product(size_t, ShenandoahTargetNumRegions, 2048, EXPERIMENTAL, \ 42 "With automatic region sizing, this is the approximate number " \ 43 "of regions that would be used, within min/max region size " \ 44 "limits.") \ 45 \ 46 product(size_t, ShenandoahMinRegionSize, 256 * K, EXPERIMENTAL, \ 47 "With automatic region sizing, the regions would be at least " \ 48 "this large.") \ 49 \ 50 product(size_t, ShenandoahMaxRegionSize, 32 * M, EXPERIMENTAL, \ 51 "With automatic region sizing, the regions would be at most " \ 52 "this large.") \ 53 \ 54 product(intx, ShenandoahHumongousThreshold, 100, EXPERIMENTAL, \ 55 "Humongous objects are allocated in separate regions. " \ 56 "This setting defines how large the object should be to be " \ 57 "deemed humongous. Value is in percents of heap region size. " \ 58 "This also caps the maximum TLAB size.") \ 59 range(1, 100) \ 60 \ 61 product(ccstr, ShenandoahGCMode, "satb", \ 62 "GC mode to use. Among other things, this defines which " \ 63 "barriers are in in use. Possible values are:" \ 64 " satb - snapshot-at-the-beginning concurrent GC (three pass mark-evac-update);" \ 65 " iu - incremental-update concurrent GC (three pass mark-evac-update);" \ 66 " passive - stop the world GC only (either degenerated or full);" \ 67 " generational - generational concurrent GC") \ 68 \ 69 product(ccstr, ShenandoahGCHeuristics, "adaptive", \ 70 "GC heuristics to use. This fine-tunes the GC mode selected, " \ 71 "by choosing when to start the GC, how much to process on each " \ 72 "cycle, and what other features to automatically enable. " \ 73 "Possible values are:" \ 74 " adaptive - adapt to maintain the given amount of free heap " \ 75 "at all times, even during the GC cycle;" \ 76 " static - trigger GC when free heap falls below the threshold;" \ 77 " aggressive - run GC continuously, try to evacuate everything;" \ 78 " compact - run GC more frequently and with deeper targets to " \ 79 "free up more memory.") \ 80 \ 81 product(ccstr, ShenandoahOldGCHeuristics, "adaptive", EXPERIMENTAL, \ 82 "Similar to ShenandoahGCHeuristics, but applied to the old " \ 83 "generation. This configuration is only used to trigger old " \ 84 "collections and does not change how regions are selected " \ 85 "for collection.") \ 86 \ 87 product(uintx, ShenandoahUnloadClassesFrequency, 1, EXPERIMENTAL, \ 88 "Unload the classes every Nth cycle. Normally affects concurrent "\ 89 "GC cycles, as degenerated and full GCs would try to unload " \ 90 "classes regardless. Set to zero to disable class unloading.") \ 91 \ 92 product(uintx, ShenandoahGarbageThreshold, 25, EXPERIMENTAL, \ 93 "How much garbage a region has to contain before it would be " \ 94 "taken for collection. This a guideline only, as GC heuristics " \ 95 "may select the region for collection even if it has little " \ 96 "garbage. This also affects how much internal fragmentation the " \ 97 "collector accepts. In percents of heap region size.") \ 98 range(0,100) \ 99 \ 100 product(uintx, ShenandoahOldGarbageThreshold, 15, EXPERIMENTAL, \ 101 "How much garbage an old region has to contain before it would " \ 102 "be taken for collection.") \ 103 range(0,100) \ 104 \ 105 product(uintx, ShenandoahIgnoreGarbageThreshold, 5, EXPERIMENTAL, \ 106 "When less than this amount of garbage (as a percentage of " \ 107 "region size) exists within a region, the region will not be " \ 108 "added to the collection set, even when the heuristic has " \ 109 "chosen to aggressively add regions with less than " \ 110 "ShenandoahGarbageThreshold amount of garbage into the " \ 111 "collection set.") \ 112 range(0,100) \ 113 \ 114 product(uintx, ShenandoahInitFreeThreshold, 70, EXPERIMENTAL, \ 115 "When less than this amount of memory is free within the" \ 116 "heap or generation, trigger a learning cycle if we are " \ 117 "in learning mode. Learning mode happens during initialization " \ 118 "and following a drastic state change, such as following a " \ 119 "degenerated or Full GC cycle. In percents of soft max " \ 120 "heap size.") \ 121 range(0,100) \ 122 \ 123 product(uintx, ShenandoahMinFreeThreshold, 10, EXPERIMENTAL, \ 124 "Percentage of free heap memory (or young generation, in " \ 125 "generational mode) below which most heuristics trigger " \ 126 "collection independent of other triggers. Provides a safety " \ 127 "margin for many heuristics. In percents of (soft) max heap " \ 128 "size.") \ 129 range(0,100) \ 130 \ 131 product(uintx, ShenandoahAllocationThreshold, 0, EXPERIMENTAL, \ 132 "How many new allocations should happen since the last GC cycle " \ 133 "before some heuristics trigger the collection. In percents of " \ 134 "(soft) max heap size. Set to zero to effectively disable.") \ 135 range(0,100) \ 136 \ 137 product(uintx, ShenandoahAllocSpikeFactor, 5, EXPERIMENTAL, \ 138 "How much of heap should some heuristics reserve for absorbing " \ 139 "the allocation spikes. Larger value wastes more memory in " \ 140 "non-emergency cases, but provides more safety in emergency " \ 141 "cases. In percents of (soft) max heap size.") \ 142 range(0,100) \ 143 \ 144 product(uintx, ShenandoahLearningSteps, 10, EXPERIMENTAL, \ 145 "The number of cycles some heuristics take to collect in order " \ 146 "to learn application and GC performance.") \ 147 range(0,100) \ 148 \ 149 product(uintx, ShenandoahImmediateThreshold, 70, EXPERIMENTAL, \ 150 "The cycle may shortcut when enough garbage can be reclaimed " \ 151 "from the immediate garbage (completely garbage regions). " \ 152 "In percents of total garbage found. Setting this threshold " \ 153 "to 100 effectively disables the shortcut.") \ 154 range(0,100) \ 155 \ 156 product(uintx, ShenandoahAdaptiveSampleFrequencyHz, 10, EXPERIMENTAL, \ 157 "The number of times per second to update the allocation rate " \ 158 "moving average.") \ 159 \ 160 product(uintx, ShenandoahAdaptiveSampleSizeSeconds, 10, EXPERIMENTAL, \ 161 "The size of the moving window over which the average " \ 162 "allocation rate is maintained. The total number of samples " \ 163 "is the product of this number and the sample frequency.") \ 164 \ 165 product(double, ShenandoahAdaptiveInitialConfidence, 1.8, EXPERIMENTAL, \ 166 "The number of standard deviations used to determine an initial " \ 167 "margin of error for the average cycle time and average " \ 168 "allocation rate. Increasing this value will cause the " \ 169 "heuristic to initiate more concurrent cycles." ) \ 170 \ 171 product(double, ShenandoahAdaptiveInitialSpikeThreshold, 1.8, EXPERIMENTAL, \ 172 "If the most recently sampled allocation rate is more than " \ 173 "this many standard deviations away from the moving average, " \ 174 "then a cycle is initiated. This value controls how sensitive " \ 175 "the heuristic is to allocation spikes. Decreasing this number " \ 176 "increases the sensitivity. ") \ 177 \ 178 product(double, ShenandoahAdaptiveDecayFactor, 0.1, EXPERIMENTAL, \ 179 "The decay factor (alpha) used for values in the weighted " \ 180 "moving average of cycle time and allocation rate. " \ 181 "Larger values give more weight to recent values.") \ 182 range(0,1.0) \ 183 \ 184 product(bool, ShenandoahAdaptiveIgnoreShortCycles, true, EXPERIMENTAL, \ 185 "The adaptive heuristic tracks a moving average of cycle " \ 186 "times in order to start a gc before memory is exhausted. " \ 187 "In some cases, Shenandoah may skip the evacuation and update " \ 188 "reference phases, resulting in a shorter cycle. These may skew " \ 189 "the average cycle time downward and may cause the heuristic " \ 190 "to wait too long to start a cycle. Disabling this will have " \ 191 "the gc run less often, which will reduce CPU utilization, but" \ 192 "increase the risk of degenerated cycles.") \ 193 \ 194 product(uintx, ShenandoahGuaranteedGCInterval, 5*60*1000, EXPERIMENTAL, \ 195 "Many heuristics would guarantee a concurrent GC cycle at " \ 196 "least with this interval. This is useful when large idle " \ 197 "intervals are present, where GC can run without stealing " \ 198 "time from active application. Time is in milliseconds. " \ 199 "Setting this to 0 disables the feature.") \ 200 \ 201 product(uintx, ShenandoahGuaranteedOldGCInterval, 10*60*1000, EXPERIMENTAL, \ 202 "Run a collection of the old generation at least this often. " \ 203 "Heuristics may trigger collections more frequently. Time is in " \ 204 "milliseconds. Setting this to 0 disables the feature.") \ 205 \ 206 product(uintx, ShenandoahGuaranteedYoungGCInterval, 5*60*1000, EXPERIMENTAL, \ 207 "Run a collection of the young generation at least this often. " \ 208 "Heuristics may trigger collections more frequently. Time is in " \ 209 "milliseconds. Setting this to 0 disables the feature.") \ 210 \ 211 product(bool, ShenandoahAlwaysClearSoftRefs, false, EXPERIMENTAL, \ 212 "Unconditionally clear soft references, instead of using any " \ 213 "other cleanup policy. This minimizes footprint at expense of" \ 214 "more soft reference churn in applications.") \ 215 \ 216 product(bool, ShenandoahUncommit, true, EXPERIMENTAL, \ 217 "Allow to uncommit memory under unused regions and metadata. " \ 218 "This optimizes footprint at expense of allocation latency in " \ 219 "regions that require committing back. Uncommits would be " \ 220 "disabled by some heuristics, or with static heap size.") \ 221 \ 222 product(uintx, ShenandoahUncommitDelay, 5*60*1000, EXPERIMENTAL, \ 223 "Uncommit memory for regions that were not used for more than " \ 224 "this time. First use after that would incur allocation stalls. " \ 225 "Actively used regions would never be uncommitted, because they " \ 226 "do not become unused longer than this delay. Time is in " \ 227 "milliseconds. Setting this delay to 0 effectively uncommits " \ 228 "regions almost immediately after they become unused.") \ 229 \ 230 product(bool, ShenandoahRegionSampling, false, EXPERIMENTAL, \ 231 "Provide heap region sampling data via jvmstat.") \ 232 \ 233 product(int, ShenandoahRegionSamplingRate, 40, EXPERIMENTAL, \ 234 "Sampling rate for heap region sampling. In milliseconds between "\ 235 "the samples. Higher values provide more fidelity, at expense " \ 236 "of more sampling overhead.") \ 237 \ 238 product(uintx, ShenandoahControlIntervalMin, 1, EXPERIMENTAL, \ 239 "The minimum sleep interval for the control loop that drives " \ 240 "the cycles. Lower values would increase GC responsiveness " \ 241 "to changing heap conditions, at the expense of higher perf " \ 242 "overhead. Time is in milliseconds.") \ 243 \ 244 product(uintx, ShenandoahControlIntervalMax, 10, EXPERIMENTAL, \ 245 "The maximum sleep interval for control loop that drives " \ 246 "the cycles. Lower values would increase GC responsiveness " \ 247 "to changing heap conditions, at the expense of higher perf " \ 248 "overhead. Time is in milliseconds.") \ 249 \ 250 product(uintx, ShenandoahControlIntervalAdjustPeriod, 1000, EXPERIMENTAL, \ 251 "The time period for one step in control loop interval " \ 252 "adjustment. Lower values make adjustments faster, at the " \ 253 "expense of higher perf overhead. Time is in milliseconds.") \ 254 \ 255 product(bool, ShenandoahVerify, false, DIAGNOSTIC, \ 256 "Enable internal verification. This would catch many GC bugs, " \ 257 "but it would also stall the collector during the verification, " \ 258 "which prolongs the pauses and might hide other bugs.") \ 259 \ 260 product(intx, ShenandoahVerifyLevel, 4, DIAGNOSTIC, \ 261 "Verification level, higher levels check more, taking more time. "\ 262 "Accepted values are:" \ 263 " 0 = basic heap checks; " \ 264 " 1 = previous level, plus basic region checks; " \ 265 " 2 = previous level, plus all roots; " \ 266 " 3 = previous level, plus all reachable objects; " \ 267 " 4 = previous level, plus all marked objects") \ 268 \ 269 product(bool, ShenandoahElasticTLAB, true, DIAGNOSTIC, \ 270 "Use Elastic TLABs with Shenandoah. This allows Shenandoah to " \ 271 "decrease the size of a TLAB to fit in a region's remaining space") \ 272 \ 273 product(uintx, ShenandoahEvacReserve, 5, EXPERIMENTAL, \ 274 "How much of (young-generation) heap to reserve for " \ 275 "(young-generation) evacuations. Larger values allow GC to " \ 276 "evacuate more live objects on every cycle, while leaving " \ 277 "less headroom for application to allocate while GC is " \ 278 "evacuating and updating references. This parameter is " \ 279 "consulted at the of marking, before selecting the collection " \ 280 "set. If available memory at this time is smaller than the " \ 281 "indicated reserve, the bound on collection set size is " \ 282 "adjusted downward. The size of a generational mixed " \ 283 "evacuation collection set (comprised of both young and old " \ 284 "regions) is also bounded by this parameter. In percents of " \ 285 "total (young-generation) heap size.") \ 286 range(1,100) \ 287 \ 288 product(double, ShenandoahEvacWaste, 1.2, EXPERIMENTAL, \ 289 "How much waste evacuations produce within the reserved space. " \ 290 "Larger values make evacuations more resilient against " \ 291 "evacuation conflicts, at expense of evacuating less on each " \ 292 "GC cycle. Smaller values increase the risk of evacuation " \ 293 "failures, which will trigger stop-the-world Full GC passes.") \ 294 range(1.0,100.0) \ 295 \ 296 product(double, ShenandoahOldEvacWaste, 1.4, EXPERIMENTAL, \ 297 "How much waste evacuations produce within the reserved space. " \ 298 "Larger values make evacuations more resilient against " \ 299 "evacuation conflicts, at expense of evacuating less on each " \ 300 "GC cycle. Smaller values increase the risk of evacuation " \ 301 "failures, which will trigger stop-the-world Full GC passes.") \ 302 range(1.0,100.0) \ 303 \ 304 product(double, ShenandoahPromoEvacWaste, 1.2, EXPERIMENTAL, \ 305 "How much waste promotions produce within the reserved space. " \ 306 "Larger values make evacuations more resilient against " \ 307 "evacuation conflicts, at expense of promoting less on each " \ 308 "GC cycle. Smaller values increase the risk of evacuation " \ 309 "failures, which will trigger stop-the-world Full GC passes.") \ 310 range(1.0,100.0) \ 311 \ 312 product(uintx, ShenandoahMaxEvacLABRatio, 0, EXPERIMENTAL, \ 313 "Potentially, each running thread maintains a PLAB for " \ 314 "evacuating objects into old-gen memory and a GCLAB for " \ 315 "evacuating objects into young-gen memory. Each time a thread " \ 316 "exhausts its PLAB or GCLAB, a new local buffer is allocated. " \ 317 "By default, the new buffer is twice the size of the previous " \ 318 "buffer. The sizes are reset to the minimum at the start of " \ 319 "each GC pass. This parameter limits the growth of evacuation " \ 320 "buffer sizes to its value multiplied by the minimum buffer " \ 321 "size. A higher value allows evacuation allocations to be more " \ 322 "efficient because less synchronization is required by " \ 323 "individual threads. However, a larger value increases the " \ 324 "likelihood of evacuation failures, leading to long " \ 325 "stop-the-world pauses. This is because a large value " \ 326 "allows individual threads to consume large percentages of " \ 327 "the total evacuation budget without necessarily effectively " \ 328 "filling their local evacuation buffers with evacuated " \ 329 "objects. A value of zero means no maximum size is enforced.") \ 330 range(0, 1024) \ 331 \ 332 product(bool, ShenandoahEvacReserveOverflow, true, EXPERIMENTAL, \ 333 "Allow evacuations to overflow the reserved space. Enabling it " \ 334 "will make evacuations more resilient when evacuation " \ 335 "reserve/waste is incorrect, at the risk that application " \ 336 "runs out of memory too early.") \ 337 \ 338 product(uintx, ShenandoahOldEvacRatioPercent, 75, EXPERIMENTAL, \ 339 "The maximum proportion of evacuation from old-gen memory, as " \ 340 "a percent ratio. The default value 75 denotes that no more " \ 341 "than 75% of the collection set evacuation " \ 342 "workload may be evacuate to old-gen heap regions. This limits " \ 343 "both the promotion of aged regions and the compaction of " \ 344 "existing old regions. A value of 75 denotes that the normal " \ 345 "young-gen evacuation is increased by up to four fold. " \ 346 "A larger value allows quicker promotion and allows" \ 347 "a smaller number of mixed evacuations to process " \ 348 "the entire list of old-gen collection candidates at the cost " \ 349 "of an increased disruption of the normal cadence of young-gen " \ 350 "collections. A value of 100 allows a mixed evacuation to " \ 351 "focus entirely on old-gen memory, allowing no young-gen " \ 352 "regions to be collected, likely resulting in subsequent " \ 353 "allocation failures because the allocation pool is not " \ 354 "replenished. A value of 0 allows a mixed evacuation to" \ 355 "focus entirely on young-gen memory, allowing no old-gen " \ 356 "regions to be collected, likely resulting in subsequent " \ 357 "promotion failures and triggering of stop-the-world full GC " \ 358 "events.") \ 359 range(0,100) \ 360 \ 361 product(uintx, ShenandoahMinYoungPercentage, 20, EXPERIMENTAL, \ 362 "The minimum percentage of the heap to use for the young " \ 363 "generation. Heuristics will not adjust the young generation " \ 364 "to be less than this.") \ 365 range(0, 100) \ 366 \ 367 product(uintx, ShenandoahMaxYoungPercentage, 100, EXPERIMENTAL, \ 368 "The maximum percentage of the heap to use for the young " \ 369 "generation. Heuristics will not adjust the young generation " \ 370 "to be more than this.") \ 371 range(0, 100) \ 372 \ 373 product(bool, ShenandoahPacing, true, EXPERIMENTAL, \ 374 "Pace application allocations to give GC chance to start " \ 375 "and complete before allocation failure is reached.") \ 376 \ 377 product(uintx, ShenandoahPacingMaxDelay, 10, EXPERIMENTAL, \ 378 "Max delay for pacing application allocations. Larger values " \ 379 "provide more resilience against out of memory, at expense at " \ 380 "hiding the GC latencies in the allocation path. Time is in " \ 381 "milliseconds. Setting it to arbitrarily large value makes " \ 382 "GC effectively stall the threads indefinitely instead of going " \ 383 "to degenerated or Full GC.") \ 384 \ 385 product(uintx, ShenandoahPacingIdleSlack, 2, EXPERIMENTAL, \ 386 "How much of heap counted as non-taxable allocations during idle "\ 387 "phases. Larger value makes the pacing milder when collector is " \ 388 "idle, requiring less rendezvous with control thread. Lower " \ 389 "value makes the pacing control less responsive to out-of-cycle " \ 390 "allocs. In percent of total heap size.") \ 391 range(0, 100) \ 392 \ 393 product(uintx, ShenandoahPacingCycleSlack, 10, EXPERIMENTAL, \ 394 "How much of free space to take as non-taxable allocations " \ 395 "the GC cycle. Larger value makes the pacing milder at the " \ 396 "beginning of the GC cycle. Lower value makes the pacing less " \ 397 "uniform during the cycle. In percent of free space.") \ 398 range(0, 100) \ 399 \ 400 product(double, ShenandoahPacingSurcharge, 1.1, EXPERIMENTAL, \ 401 "Additional pacing tax surcharge to help unclutter the heap. " \ 402 "Larger values makes the pacing more aggressive. Lower values " \ 403 "risk GC cycles finish with less memory than were available at " \ 404 "the beginning of it.") \ 405 range(1.0, 100.0) \ 406 \ 407 product(uintx, ShenandoahCriticalFreeThreshold, 1, EXPERIMENTAL, \ 408 "How much of the heap needs to be free after recovery cycles, " \ 409 "either Degenerated or Full GC to be claimed successful. If this "\ 410 "much space is not available, next recovery step would be " \ 411 "triggered.") \ 412 range(0, 100) \ 413 \ 414 product(bool, ShenandoahDegeneratedGC, true, DIAGNOSTIC, \ 415 "Enable Degenerated GC as the graceful degradation step. " \ 416 "Disabling this option leads to degradation to Full GC instead. " \ 417 "When running in passive mode, this can be toggled to measure " \ 418 "either Degenerated GC or Full GC costs.") \ 419 \ 420 product(uintx, ShenandoahFullGCThreshold, 64, EXPERIMENTAL, \ 421 "How many back-to-back Degenerated GCs should happen before " \ 422 "going to a Full GC.") \ 423 \ 424 product(uintx, ShenandoahOOMGCRetries, 3, EXPERIMENTAL, \ 425 "How many GCs should happen before we throw OutOfMemoryException "\ 426 "for allocation request, including at least one Full GC.") \ 427 \ 428 product(bool, ShenandoahImplicitGCInvokesConcurrent, false, EXPERIMENTAL, \ 429 "Should internally-caused GC requests invoke concurrent cycles, " \ 430 "should they do the stop-the-world (Degenerated / Full GC)? " \ 431 "Many heuristics automatically enable this. This option is " \ 432 "similar to global ExplicitGCInvokesConcurrent.") \ 433 \ 434 product(bool, ShenandoahHumongousMoves, true, DIAGNOSTIC, \ 435 "Allow moving humongous regions. This makes GC more resistant " \ 436 "to external fragmentation that may otherwise fail other " \ 437 "humongous allocations, at the expense of higher GC copying " \ 438 "costs. Currently affects stop-the-world (Full) cycle only.") \ 439 \ 440 product(bool, ShenandoahOOMDuringEvacALot, false, DIAGNOSTIC, \ 441 "Testing: simulate OOM during evacuation.") \ 442 \ 443 product(bool, ShenandoahAllocFailureALot, false, DIAGNOSTIC, \ 444 "Testing: make lots of artificial allocation failures.") \ 445 \ 446 product(uintx, ShenandoahCoalesceChance, 0, DIAGNOSTIC, \ 447 "Testing: Abandon remaining mixed collections with this " \ 448 "likelihood. Following each mixed collection, abandon all " \ 449 "remaining mixed collection candidate regions with likelihood " \ 450 "ShenandoahCoalesceChance. Abandoning a mixed collection will " \ 451 "cause the old regions to be made parseable, rather than being " \ 452 "evacuated.") \ 453 range(0, 100) \ 454 \ 455 product(intx, ShenandoahMarkScanPrefetch, 32, EXPERIMENTAL, \ 456 "How many objects to prefetch ahead when traversing mark bitmaps."\ 457 "Set to 0 to disable prefetching.") \ 458 range(0, 256) \ 459 \ 460 product(uintx, ShenandoahMarkLoopStride, 1000, EXPERIMENTAL, \ 461 "How many items to process during one marking iteration before " \ 462 "checking for cancellation, yielding, etc. Larger values improve "\ 463 "marking performance at expense of responsiveness.") \ 464 \ 465 product(uintx, ShenandoahParallelRegionStride, 1024, EXPERIMENTAL, \ 466 "How many regions to process at once during parallel region " \ 467 "iteration. Affects heaps with lots of regions.") \ 468 \ 469 product(size_t, ShenandoahSATBBufferSize, 1 * K, EXPERIMENTAL, \ 470 "Number of entries in an SATB log buffer.") \ 471 range(1, max_uintx) \ 472 \ 473 product(uintx, ShenandoahMaxSATBBufferFlushes, 5, EXPERIMENTAL, \ 474 "How many times to maximum attempt to flush SATB buffers at the " \ 475 "end of concurrent marking.") \ 476 \ 477 product(bool, ShenandoahSuspendibleWorkers, true, EXPERIMENTAL, \ 478 "Suspend concurrent GC worker threads at safepoints") \ 479 \ 480 product(bool, ShenandoahSATBBarrier, true, DIAGNOSTIC, \ 481 "Turn on/off SATB barriers in Shenandoah") \ 482 \ 483 product(bool, ShenandoahIUBarrier, false, DIAGNOSTIC, \ 484 "Turn on/off I-U barriers barriers in Shenandoah") \ 485 \ 486 product(bool, ShenandoahCASBarrier, true, DIAGNOSTIC, \ 487 "Turn on/off CAS barriers in Shenandoah") \ 488 \ 489 product(bool, ShenandoahCloneBarrier, true, DIAGNOSTIC, \ 490 "Turn on/off clone barriers in Shenandoah") \ 491 \ 492 product(bool, ShenandoahLoadRefBarrier, true, DIAGNOSTIC, \ 493 "Turn on/off load-reference barriers in Shenandoah") \ 494 \ 495 product(bool, ShenandoahNMethodBarrier, true, DIAGNOSTIC, \ 496 "Turn on/off NMethod entry barriers in Shenandoah") \ 497 \ 498 product(bool, ShenandoahStackWatermarkBarrier, true, DIAGNOSTIC, \ 499 "Turn on/off stack watermark barriers in Shenandoah") \ 500 \ 501 develop(bool, ShenandoahVerifyOptoBarriers, false, \ 502 "Verify no missing barriers in C2.") \ 503 \ 504 product(bool, ShenandoahLoopOptsAfterExpansion, true, DIAGNOSTIC, \ 505 "Attempt more loop opts after barrier expansion.") \ 506 \ 507 product(bool, ShenandoahSelfFixing, true, DIAGNOSTIC, \ 508 "Fix references with load reference barrier. Disabling this " \ 509 "might degrade performance.") \ 510 \ 511 product(uintx, ShenandoahOldCompactionReserve, 8, EXPERIMENTAL, \ 512 "During generational GC, prevent promotions from filling " \ 513 "this number of heap regions. These regions are reserved " \ 514 "for the purpose of supporting compaction of old-gen " \ 515 "memory. Otherwise, old-gen memory cannot be compacted.") \ 516 range(0, 128) \ 517 \ 518 product(bool, ShenandoahAllowOldMarkingPreemption, true, DIAGNOSTIC, \ 519 "Allow young generation collections to suspend concurrent" \ 520 " marking in the old generation.") \ 521 \ 522 product(uintx, ShenandoahAgingCyclePeriod, 1, EXPERIMENTAL, \ 523 "With generational mode, increment the age of objects and" \ 524 "regions each time this many young-gen GC cycles are completed.") \ 525 \ 526 notproduct(bool, ShenandoahEnableCardStats, trueInDebug, \ 527 "Enable statistics collection related to clean & dirty cards") \ 528 \ 529 notproduct(int, ShenandoahCardStatsLogInterval, 50, \ 530 "Log cumulative card stats every so many remembered set or " \ 531 "update refs scans") \ 532 // end of GC_SHENANDOAH_FLAGS 533 534 #endif // SHARE_GC_SHENANDOAH_SHENANDOAH_GLOBALS_HPP