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 \ 67 product(ccstr, ShenandoahGCHeuristics, "adaptive", \ 68 "GC heuristics to use. This fine-tunes the GC mode selected, " \ 69 "by choosing when to start the GC, how much to process on each " \ 70 "cycle, and what other features to automatically enable. " \ 71 "Possible values are:" \ 72 " adaptive - adapt to maintain the given amount of free heap " \ 73 "at all times, even during the GC cycle;" \ 74 " static - trigger GC when free heap falls below the threshold;" \ 75 " aggressive - run GC continuously, try to evacuate everything;" \ 76 " compact - run GC more frequently and with deeper targets to " \ 77 "free up more memory.") \ 78 \ 79 product(uintx, ShenandoahGarbageThreshold, 25, EXPERIMENTAL, \ 80 "How much garbage a region has to contain before it would be " \ 81 "taken for collection. This a guideline only, as GC heuristics " \ 82 "may select the region for collection even if it has little " \ 83 "garbage. This also affects how much internal fragmentation the " \ 84 "collector accepts. In percents of heap region size.") \ 85 range(0,100) \ 86 \ 87 product(uintx, ShenandoahInitFreeThreshold, 70, EXPERIMENTAL, \ 88 "How much heap should be free before some heuristics trigger the "\ 89 "initial (learning) cycles. Affects cycle frequency on startup " \ 90 "and after drastic state changes, e.g. after degenerated/full " \ 91 "GC cycles. In percents of (soft) max heap size.") \ 92 range(0,100) \ 93 \ 94 product(uintx, ShenandoahMinFreeThreshold, 10, EXPERIMENTAL, \ 95 "How much heap should be free before most heuristics trigger the "\ 96 "collection, even without other triggers. Provides the safety " \ 97 "margin for many heuristics. In percents of (soft) max heap size.")\ 98 range(0,100) \ 99 \ 100 product(uintx, ShenandoahAllocationThreshold, 0, EXPERIMENTAL, \ 101 "How many new allocations should happen since the last GC cycle " \ 102 "before some heuristics trigger the collection. In percents of " \ 103 "(soft) max heap size. Set to zero to effectively disable.") \ 104 range(0,100) \ 105 \ 106 product(uintx, ShenandoahAllocSpikeFactor, 5, EXPERIMENTAL, \ 107 "How much of heap should some heuristics reserve for absorbing " \ 108 "the allocation spikes. Larger value wastes more memory in " \ 109 "non-emergency cases, but provides more safety in emergency " \ 110 "cases. In percents of (soft) max heap size.") \ 111 range(0,100) \ 112 \ 113 product(uintx, ShenandoahLearningSteps, 5, EXPERIMENTAL, \ 114 "The number of cycles some heuristics take to collect in order " \ 115 "to learn application and GC performance.") \ 116 range(0,100) \ 117 \ 118 product(uintx, ShenandoahImmediateThreshold, 90, EXPERIMENTAL, \ 119 "The cycle may shortcut when enough garbage can be reclaimed " \ 120 "from the immediate garbage (completely garbage regions). " \ 121 "In percents of total garbage found. Setting this threshold " \ 122 "to 100 effectively disables the shortcut.") \ 123 range(0,100) \ 124 \ 125 product(uintx, ShenandoahAdaptiveSampleFrequencyHz, 10, EXPERIMENTAL, \ 126 "The number of times per second to update the allocation rate " \ 127 "moving average.") \ 128 \ 129 product(uintx, ShenandoahAdaptiveSampleSizeSeconds, 10, EXPERIMENTAL, \ 130 "The size of the moving window over which the average " \ 131 "allocation rate is maintained. The total number of samples " \ 132 "is the product of this number and the sample frequency.") \ 133 \ 134 product(double, ShenandoahAdaptiveInitialConfidence, 1.8, EXPERIMENTAL, \ 135 "The number of standard deviations used to determine an initial " \ 136 "margin of error for the average cycle time and average " \ 137 "allocation rate. Increasing this value will cause the " \ 138 "heuristic to initiate more concurrent cycles." ) \ 139 \ 140 product(double, ShenandoahAdaptiveInitialSpikeThreshold, 1.8, EXPERIMENTAL, \ 141 "If the most recently sampled allocation rate is more than " \ 142 "this many standard deviations away from the moving average, " \ 143 "then a cycle is initiated. This value controls how sensitive " \ 144 "the heuristic is to allocation spikes. Decreasing this number " \ 145 "increases the sensitivity. ") \ 146 \ 147 product(double, ShenandoahAdaptiveDecayFactor, 0.5, EXPERIMENTAL, \ 148 "The decay factor (alpha) used for values in the weighted " \ 149 "moving average of cycle time and allocation rate. " \ 150 "Larger values give more weight to recent values.") \ 151 range(0,1.0) \ 152 \ 153 product(uintx, ShenandoahGuaranteedGCInterval, 5*60*1000, EXPERIMENTAL, \ 154 "Many heuristics would guarantee a concurrent GC cycle at " \ 155 "least with this interval. This is useful when large idle " \ 156 "intervals are present, where GC can run without stealing " \ 157 "time from active application. Time is in milliseconds. " \ 158 "Setting this to 0 disables the feature.") \ 159 \ 160 product(bool, ShenandoahAlwaysClearSoftRefs, false, EXPERIMENTAL, \ 161 "Unconditionally clear soft references, instead of using any " \ 162 "other cleanup policy. This minimizes footprint at expense of" \ 163 "more soft reference churn in applications.") \ 164 \ 165 product(bool, ShenandoahUncommit, true, EXPERIMENTAL, \ 166 "Allow to uncommit memory under unused regions and metadata. " \ 167 "This optimizes footprint at expense of allocation latency in " \ 168 "regions that require committing back. Uncommits would be " \ 169 "disabled by some heuristics, or with static heap size.") \ 170 \ 171 product(uintx, ShenandoahUncommitDelay, 5*60*1000, EXPERIMENTAL, \ 172 "Uncommit memory for regions that were not used for more than " \ 173 "this time. First use after that would incur allocation stalls. " \ 174 "Actively used regions would never be uncommitted, because they " \ 175 "do not become unused longer than this delay. Time is in " \ 176 "milliseconds. Setting this delay to 0 effectively uncommits " \ 177 "regions almost immediately after they become unused.") \ 178 \ 179 product(bool, ShenandoahRegionSampling, false, EXPERIMENTAL, \ 180 "Provide heap region sampling data via jvmstat.") \ 181 \ 182 product(int, ShenandoahRegionSamplingRate, 40, EXPERIMENTAL, \ 183 "Sampling rate for heap region sampling. In milliseconds between "\ 184 "the samples. Higher values provide more fidelity, at expense " \ 185 "of more sampling overhead.") \ 186 \ 187 product(uintx, ShenandoahControlIntervalMin, 1, EXPERIMENTAL, \ 188 "The minimum sleep interval for the control loop that drives " \ 189 "the cycles. Lower values would increase GC responsiveness " \ 190 "to changing heap conditions, at the expense of higher perf " \ 191 "overhead. Time is in milliseconds.") \ 192 \ 193 product(uintx, ShenandoahControlIntervalMax, 10, EXPERIMENTAL, \ 194 "The maximum sleep interval for control loop that drives " \ 195 "the cycles. Lower values would increase GC responsiveness " \ 196 "to changing heap conditions, at the expense of higher perf " \ 197 "overhead. Time is in milliseconds.") \ 198 \ 199 product(uintx, ShenandoahControlIntervalAdjustPeriod, 1000, EXPERIMENTAL, \ 200 "The time period for one step in control loop interval " \ 201 "adjustment. Lower values make adjustments faster, at the " \ 202 "expense of higher perf overhead. Time is in milliseconds.") \ 203 \ 204 product(bool, ShenandoahVerify, false, DIAGNOSTIC, \ 205 "Enable internal verification. This would catch many GC bugs, " \ 206 "but it would also stall the collector during the verification, " \ 207 "which prolongs the pauses and might hide other bugs.") \ 208 \ 209 product(intx, ShenandoahVerifyLevel, 4, DIAGNOSTIC, \ 210 "Verification level, higher levels check more, taking more time. "\ 211 "Accepted values are:" \ 212 " 0 = basic heap checks; " \ 213 " 1 = previous level, plus basic region checks; " \ 214 " 2 = previous level, plus all roots; " \ 215 " 3 = previous level, plus all reachable objects; " \ 216 " 4 = previous level, plus all marked objects") \ 217 \ 218 product(uintx, ShenandoahEvacReserve, 5, EXPERIMENTAL, \ 219 "How much of heap to reserve for evacuations. Larger values make "\ 220 "GC evacuate more live objects on every cycle, while leaving " \ 221 "less headroom for application to allocate in. In percents of " \ 222 "total heap size.") \ 223 range(1,100) \ 224 \ 225 product(double, ShenandoahEvacWaste, 1.2, EXPERIMENTAL, \ 226 "How much waste evacuations produce within the reserved space. " \ 227 "Larger values make evacuations more resilient against " \ 228 "evacuation conflicts, at expense of evacuating less on each " \ 229 "GC cycle.") \ 230 range(1.0,100.0) \ 231 \ 232 product(bool, ShenandoahEvacReserveOverflow, true, EXPERIMENTAL, \ 233 "Allow evacuations to overflow the reserved space. Enabling it " \ 234 "will make evacuations more resilient when evacuation " \ 235 "reserve/waste is incorrect, at the risk that application " \ 236 "runs out of memory too early.") \ 237 \ 238 product(bool, ShenandoahPacing, true, EXPERIMENTAL, \ 239 "Pace application allocations to give GC chance to start " \ 240 "and complete before allocation failure is reached.") \ 241 \ 242 product(uintx, ShenandoahPacingMaxDelay, 10, EXPERIMENTAL, \ 243 "Max delay for pacing application allocations. Larger values " \ 244 "provide more resilience against out of memory, at expense at " \ 245 "hiding the GC latencies in the allocation path. Time is in " \ 246 "milliseconds. Setting it to arbitrarily large value makes " \ 247 "GC effectively stall the threads indefinitely instead of going " \ 248 "to degenerated or Full GC.") \ 249 \ 250 product(uintx, ShenandoahPacingIdleSlack, 2, EXPERIMENTAL, \ 251 "How much of heap counted as non-taxable allocations during idle "\ 252 "phases. Larger value makes the pacing milder when collector is " \ 253 "idle, requiring less rendezvous with control thread. Lower " \ 254 "value makes the pacing control less responsive to out-of-cycle " \ 255 "allocs. In percent of total heap size.") \ 256 range(0, 100) \ 257 \ 258 product(uintx, ShenandoahPacingCycleSlack, 10, EXPERIMENTAL, \ 259 "How much of free space to take as non-taxable allocations " \ 260 "the GC cycle. Larger value makes the pacing milder at the " \ 261 "beginning of the GC cycle. Lower value makes the pacing less " \ 262 "uniform during the cycle. In percent of free space.") \ 263 range(0, 100) \ 264 \ 265 product(double, ShenandoahPacingSurcharge, 1.1, EXPERIMENTAL, \ 266 "Additional pacing tax surcharge to help unclutter the heap. " \ 267 "Larger values makes the pacing more aggressive. Lower values " \ 268 "risk GC cycles finish with less memory than were available at " \ 269 "the beginning of it.") \ 270 range(1.0, 100.0) \ 271 \ 272 product(uintx, ShenandoahCriticalFreeThreshold, 1, EXPERIMENTAL, \ 273 "How much of the heap needs to be free after recovery cycles, " \ 274 "either Degenerated or Full GC to be claimed successful. If this "\ 275 "much space is not available, next recovery step would be " \ 276 "triggered.") \ 277 range(0, 100) \ 278 \ 279 product(bool, ShenandoahDegeneratedGC, true, DIAGNOSTIC, \ 280 "Enable Degenerated GC as the graceful degradation step. " \ 281 "Disabling this option leads to degradation to Full GC instead. " \ 282 "When running in passive mode, this can be toggled to measure " \ 283 "either Degenerated GC or Full GC costs.") \ 284 \ 285 product(uintx, ShenandoahFullGCThreshold, 3, EXPERIMENTAL, \ 286 "How many back-to-back Degenerated GCs should happen before " \ 287 "going to a Full GC.") \ 288 \ 289 product(bool, ShenandoahImplicitGCInvokesConcurrent, false, EXPERIMENTAL, \ 290 "Should internally-caused GC requests invoke concurrent cycles, " \ 291 "should they do the stop-the-world (Degenerated / Full GC)? " \ 292 "Many heuristics automatically enable this. This option is " \ 293 "similar to global ExplicitGCInvokesConcurrent.") \ 294 \ 295 product(bool, ShenandoahHumongousMoves, true, DIAGNOSTIC, \ 296 "Allow moving humongous regions. This makes GC more resistant " \ 297 "to external fragmentation that may otherwise fail other " \ 298 "humongous allocations, at the expense of higher GC copying " \ 299 "costs. Currently affects stop-the-world (Full) cycle only.") \ 300 \ 301 product(bool, ShenandoahOOMDuringEvacALot, false, DIAGNOSTIC, \ 302 "Testing: simulate OOM during evacuation.") \ 303 \ 304 product(bool, ShenandoahAllocFailureALot, false, DIAGNOSTIC, \ 305 "Testing: make lots of artificial allocation failures.") \ 306 \ 307 product(intx, ShenandoahMarkScanPrefetch, 32, EXPERIMENTAL, \ 308 "How many objects to prefetch ahead when traversing mark bitmaps."\ 309 "Set to 0 to disable prefetching.") \ 310 range(0, 256) \ 311 \ 312 product(uintx, ShenandoahMarkLoopStride, 1000, EXPERIMENTAL, \ 313 "How many items to process during one marking iteration before " \ 314 "checking for cancellation, yielding, etc. Larger values improve "\ 315 "marking performance at expense of responsiveness.") \ 316 \ 317 product(uintx, ShenandoahParallelRegionStride, 1024, EXPERIMENTAL, \ 318 "How many regions to process at once during parallel region " \ 319 "iteration. Affects heaps with lots of regions.") \ 320 \ 321 product(size_t, ShenandoahSATBBufferSize, 1 * K, EXPERIMENTAL, \ 322 "Number of entries in an SATB log buffer.") \ 323 range(1, max_uintx) \ 324 \ 325 product(uintx, ShenandoahMaxSATBBufferFlushes, 5, EXPERIMENTAL, \ 326 "How many times to maximum attempt to flush SATB buffers at the " \ 327 "end of concurrent marking.") \ 328 \ 329 product(bool, ShenandoahSATBBarrier, true, DIAGNOSTIC, \ 330 "Turn on/off SATB barriers in Shenandoah") \ 331 \ 332 product(bool, ShenandoahIUBarrier, false, DIAGNOSTIC, \ 333 "Turn on/off I-U barriers barriers in Shenandoah") \ 334 \ 335 product(bool, ShenandoahCASBarrier, true, DIAGNOSTIC, \ 336 "Turn on/off CAS barriers in Shenandoah") \ 337 \ 338 product(bool, ShenandoahCloneBarrier, true, DIAGNOSTIC, \ 339 "Turn on/off clone barriers in Shenandoah") \ 340 \ 341 product(bool, ShenandoahLoadRefBarrier, true, DIAGNOSTIC, \ 342 "Turn on/off load-reference barriers in Shenandoah") \ 343 \ 344 product(bool, ShenandoahStackWatermarkBarrier, true, DIAGNOSTIC, \ 345 "Turn on/off stack watermark barriers in Shenandoah") \ 346 \ 347 develop(bool, ShenandoahVerifyOptoBarriers, trueInDebug, \ 348 "Verify no missing barriers in C2.") \ 349 \ 350 351 // end of GC_SHENANDOAH_FLAGS 352 353 #endif // SHARE_GC_SHENANDOAH_SHENANDOAH_GLOBALS_HPP --- EOF ---