/* * Copyright (c) 2020, 2024, Oracle and/or its affiliates. All rights reserved. * Copyright (c) 2016, 2021, Red Hat, Inc. All rights reserved. * Copyright Amazon.com Inc. or its affiliates. All Rights Reserved. * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. * * This code is free software; you can redistribute it and/or modify it * under the terms of the GNU General Public License version 2 only, as * published by the Free Software Foundation. * * This code is distributed in the hope that it will be useful, but WITHOUT * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License * version 2 for more details (a copy is included in the LICENSE file that * accompanied this code). * * You should have received a copy of the GNU General Public License version * 2 along with this work; if not, write to the Free Software Foundation, * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. * * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA * or visit www.oracle.com if you need additional information or have any * questions. * */ #ifndef SHARE_GC_SHENANDOAH_SHENANDOAH_GLOBALS_HPP #define SHARE_GC_SHENANDOAH_SHENANDOAH_GLOBALS_HPP #define GC_SHENANDOAH_FLAGS(develop, \ develop_pd, \ product, \ product_pd, \ range, \ constraint) \ \ product(uintx, ShenandoahGenerationalHumongousReserve, 0, EXPERIMENTAL, \ "(Generational mode only) What percent of the heap should be " \ "reserved for humongous objects if possible. Old-generation " \ "collections will endeavor to evacuate old-gen regions within " \ "this reserved area even if these regions do not contain high " \ "percentage of garbage. Setting a larger value will cause " \ "more frequent old-gen collections. A smaller value will " \ "increase the likelihood that humongous object allocations " \ "fail, resulting in stop-the-world full GCs.") \ range(0,100) \ \ product(double, ShenandoahMinOldGenGrowthPercent, 12.5, EXPERIMENTAL, \ "(Generational mode only) If the usage within old generation " \ "has grown by at least this percent of its live memory size " \ "at completion of the most recent old-generation marking " \ "effort, heuristics may trigger the start of a new old-gen " \ "collection.") \ range(0.0,100.0) \ \ product(uintx, ShenandoahIgnoreOldGrowthBelowPercentage,10, EXPERIMENTAL, \ "(Generational mode only) If the total usage of the old " \ "generation is smaller than this percent, we do not trigger " \ "old gen collections even if old has grown, except when " \ "ShenandoahGenerationalDoNotIgnoreGrowthAfterYoungCycles " \ "consecutive cycles have been completed following the " \ "preceding old-gen collection.") \ range(0,100) \ \ product(uintx, ShenandoahDoNotIgnoreGrowthAfterYoungCycles, \ 50, EXPERIMENTAL, \ "(Generational mode only) Even if the usage of old generation " \ "is below ShenandoahIgnoreOldGrowthBelowPercentage, " \ "trigger an old-generation mark if old has grown and this " \ "many consecutive young-gen collections have been " \ "completed following the preceding old-gen collection.") \ \ product(bool, ShenandoahGenerationalCensusAtEvac, false, EXPERIMENTAL, \ "(Generational mode only) Object age census at evacuation, " \ "rather than during marking.") \ \ product(bool, ShenandoahGenerationalAdaptiveTenuring, true, EXPERIMENTAL, \ "(Generational mode only) Dynamically adapt tenuring age.") \ \ product(bool, ShenandoahGenerationalCensusIgnoreOlderCohorts, true, \ EXPERIMENTAL,\ "(Generational mode only) Ignore mortality rates older than the " \ "oldest cohort under the tenuring age for the last cycle." ) \ \ product(uintx, ShenandoahGenerationalMinTenuringAge, 1, EXPERIMENTAL, \ "(Generational mode only) Floor for adaptive tenuring age. " \ "Setting floor and ceiling to the same value fixes the tenuring " \ "age; setting both to 1 simulates a poor approximation to " \ "AlwaysTenure, and setting both to 16 simulates NeverTenure.") \ range(1,16) \ \ product(uintx, ShenandoahGenerationalMaxTenuringAge, 15, EXPERIMENTAL, \ "(Generational mode only) Ceiling for adaptive tenuring age. " \ "Setting floor and ceiling to the same value fixes the tenuring " \ "age; setting both to 1 simulates a poor approximation to " \ "AlwaysTenure, and setting both to 16 simulates NeverTenure.") \ range(1,16) \ \ product(double, ShenandoahGenerationalTenuringMortalityRateThreshold, \ 0.1, EXPERIMENTAL, \ "(Generational mode only) Cohort mortality rates below this " \ "value will be treated as indicative of longevity, leading to " \ "tenuring. A lower value delays tenuring, a higher value hastens "\ "it. Used only when ShenandoahGenerationalhenAdaptiveTenuring is "\ "enabled.") \ range(0.001,0.999) \ \ product(size_t, ShenandoahGenerationalTenuringCohortPopulationThreshold, \ 4*K, EXPERIMENTAL, \ "(Generational mode only) Cohorts whose population is lower than "\ "this value in the previous census are ignored wrt tenuring " \ "decisions. Effectively this makes then tenurable as soon as all "\ "older cohorts are. Set this value to the largest cohort " \ "population volume that you are comfortable ignoring when making "\ "tenuring decisions.") \ \ product(size_t, ShenandoahRegionSize, 0, EXPERIMENTAL, \ "Static heap region size. Set zero to enable automatic sizing.") \ \ product(size_t, ShenandoahTargetNumRegions, 2048, EXPERIMENTAL, \ "With automatic region sizing, this is the approximate number " \ "of regions that would be used, within min/max region size " \ "limits.") \ \ product(size_t, ShenandoahMinRegionSize, 256 * K, EXPERIMENTAL, \ "With automatic region sizing, the regions would be at least " \ "this large.") \ \ product(size_t, ShenandoahMaxRegionSize, 32 * M, EXPERIMENTAL, \ "With automatic region sizing, the regions would be at most " \ "this large.") \ \ product(ccstr, ShenandoahGCMode, "satb", \ "GC mode to use. Among other things, this defines which " \ "barriers are in in use. Possible values are:" \ " satb - snapshot-at-the-beginning concurrent GC (three pass mark-evac-update);" \ " passive - stop the world GC only (either degenerated or full);" \ " generational - generational concurrent GC") \ \ product(ccstr, ShenandoahGCHeuristics, "adaptive", \ "GC heuristics to use. This fine-tunes the GC mode selected, " \ "by choosing when to start the GC, how much to process on each " \ "cycle, and what other features to automatically enable. " \ "Possible values are:" \ " adaptive - adapt to maintain the given amount of free heap " \ "at all times, even during the GC cycle;" \ " static - trigger GC when free heap falls below the threshold;" \ " aggressive - run GC continuously, try to evacuate everything;" \ " compact - run GC more frequently and with deeper targets to " \ "free up more memory.") \ \ product(uintx, ShenandoahExpeditePromotionsThreshold, 5, EXPERIMENTAL, \ "When Shenandoah expects to promote at least this percentage " \ "of the young generation, trigger a young collection to " \ "expedite these promotions.") \ range(0,100) \ \ product(uintx, ShenandoahExpediteMixedThreshold, 10, EXPERIMENTAL, \ "When there are this many old regions waiting to be collected, " \ "trigger a mixed collection immediately.") \ \ product(uintx, ShenandoahGarbageThreshold, 25, EXPERIMENTAL, \ "How much garbage a region has to contain before it would be " \ "taken for collection. This a guideline only, as GC heuristics " \ "may select the region for collection even if it has little " \ "garbage. This also affects how much internal fragmentation the " \ "collector accepts. In percents of heap region size.") \ range(0,100) \ \ product(uintx, ShenandoahOldGarbageThreshold, 15, EXPERIMENTAL, \ "How much garbage an old region has to contain before it would " \ "be taken for collection.") \ range(0,100) \ \ product(uintx, ShenandoahIgnoreGarbageThreshold, 5, EXPERIMENTAL, \ "When less than this amount of garbage (as a percentage of " \ "region size) exists within a region, the region will not be " \ "added to the collection set, even when the heuristic has " \ "chosen to aggressively add regions with less than " \ "ShenandoahGarbageThreshold amount of garbage into the " \ "collection set.") \ range(0,100) \ \ product(uintx, ShenandoahInitFreeThreshold, 70, EXPERIMENTAL, \ "When less than this amount of memory is free within the " \ "heap or generation, trigger a learning cycle if we are " \ "in learning mode. Learning mode happens during initialization " \ "and following a drastic state change, such as following a " \ "degenerated or Full GC cycle. In percents of soft max " \ "heap size.") \ range(0,100) \ \ product(uintx, ShenandoahMinFreeThreshold, 10, EXPERIMENTAL, \ "Percentage of free heap memory (or young generation, in " \ "generational mode) below which most heuristics trigger " \ "collection independent of other triggers. Provides a safety " \ "margin for many heuristics. In percents of (soft) max heap " \ "size.") \ range(0,100) \ \ product(uintx, ShenandoahAllocationThreshold, 0, EXPERIMENTAL, \ "How many new allocations should happen since the last GC cycle " \ "before some heuristics trigger the collection. In percents of " \ "(soft) max heap size. Set to zero to effectively disable.") \ range(0,100) \ \ product(uintx, ShenandoahAllocSpikeFactor, 5, EXPERIMENTAL, \ "How much of heap should some heuristics reserve for absorbing " \ "the allocation spikes. Larger value wastes more memory in " \ "non-emergency cases, but provides more safety in emergency " \ "cases. In percents of (soft) max heap size.") \ range(0,100) \ \ product(uintx, ShenandoahLearningSteps, 5, EXPERIMENTAL, \ "The number of cycles some heuristics take to collect in order " \ "to learn application and GC performance.") \ range(0,100) \ \ product(uintx, ShenandoahImmediateThreshold, 70, EXPERIMENTAL, \ "The cycle may shortcut when enough garbage can be reclaimed " \ "from the immediate garbage (completely garbage regions). " \ "In percents of total garbage found. Setting this threshold " \ "to 100 effectively disables the shortcut.") \ range(0,100) \ \ product(uintx, ShenandoahAdaptiveSampleFrequencyHz, 10, EXPERIMENTAL, \ "The number of times per second to update the allocation rate " \ "moving average.") \ \ product(uintx, ShenandoahAdaptiveSampleSizeSeconds, 10, EXPERIMENTAL, \ "The size of the moving window over which the average " \ "allocation rate is maintained. The total number of samples " \ "is the product of this number and the sample frequency.") \ \ product(double, ShenandoahAdaptiveInitialConfidence, 1.8, EXPERIMENTAL, \ "The number of standard deviations used to determine an initial " \ "margin of error for the average cycle time and average " \ "allocation rate. Increasing this value will cause the " \ "heuristic to initiate more concurrent cycles." ) \ \ product(double, ShenandoahAdaptiveInitialSpikeThreshold, 1.8, EXPERIMENTAL, \ "If the most recently sampled allocation rate is more than " \ "this many standard deviations away from the moving average, " \ "then a cycle is initiated. This value controls how sensitive " \ "the heuristic is to allocation spikes. Decreasing this number " \ "increases the sensitivity. ") \ \ product(double, ShenandoahAdaptiveDecayFactor, 0.5, EXPERIMENTAL, \ "The decay factor (alpha) used for values in the weighted " \ "moving average of cycle time and allocation rate. " \ "Larger values give more weight to recent values.") \ range(0,1.0) \ \ product(uintx, ShenandoahGuaranteedGCInterval, 5*60*1000, EXPERIMENTAL, \ "Many heuristics would guarantee a concurrent GC cycle at " \ "least with this interval. This is useful when large idle " \ "intervals are present, where GC can run without stealing " \ "time from active application. Time is in milliseconds. " \ "Setting this to 0 disables the feature.") \ \ product(uintx, ShenandoahGuaranteedOldGCInterval, 10*60*1000, EXPERIMENTAL, \ "Run a collection of the old generation at least this often. " \ "Heuristics may trigger collections more frequently. Time is in " \ "milliseconds. Setting this to 0 disables the feature.") \ \ product(uintx, ShenandoahGuaranteedYoungGCInterval, 5*60*1000, EXPERIMENTAL, \ "Run a collection of the young generation at least this often. " \ "Heuristics may trigger collections more frequently. Time is in " \ "milliseconds. Setting this to 0 disables the feature.") \ \ product(bool, ShenandoahAlwaysClearSoftRefs, false, EXPERIMENTAL, \ "Unconditionally clear soft references, instead of using any " \ "other cleanup policy. This minimizes footprint at expense of" \ "more soft reference churn in applications.") \ \ product(bool, ShenandoahUncommit, true, EXPERIMENTAL, \ "Allow to uncommit memory under unused regions and metadata. " \ "This optimizes footprint at expense of allocation latency in " \ "regions that require committing back. Uncommits would be " \ "disabled by some heuristics, or with static heap size.") \ \ product(uintx, ShenandoahUncommitDelay, 5*60*1000, EXPERIMENTAL, \ "Uncommit memory for regions that were not used for more than " \ "this time. First use after that would incur allocation stalls. " \ "Actively used regions would never be uncommitted, because they " \ "do not become unused longer than this delay. Time is in " \ "milliseconds. Setting this delay to 0 effectively uncommits " \ "regions almost immediately after they become unused.") \ \ product(bool, ShenandoahRegionSampling, false, EXPERIMENTAL, \ "Provide heap region sampling data via jvmstat.") \ \ product(int, ShenandoahRegionSamplingRate, 40, EXPERIMENTAL, \ "Sampling rate for heap region sampling. In milliseconds between "\ "the samples. Higher values provide more fidelity, at expense " \ "of more sampling overhead.") \ \ product(uintx, ShenandoahControlIntervalMin, 1, EXPERIMENTAL, \ "The minimum sleep interval for the control loop that drives " \ "the cycles. Lower values would increase GC responsiveness " \ "to changing heap conditions, at the expense of higher perf " \ "overhead. Time is in milliseconds.") \ range(1, 999) \ \ product(uintx, ShenandoahControlIntervalMax, 10, EXPERIMENTAL, \ "The maximum sleep interval for control loop that drives " \ "the cycles. Lower values would increase GC responsiveness " \ "to changing heap conditions, at the expense of higher perf " \ "overhead. Time is in milliseconds.") \ range(1, 999) \ \ product(uintx, ShenandoahControlIntervalAdjustPeriod, 1000, EXPERIMENTAL, \ "The time period for one step in control loop interval " \ "adjustment. Lower values make adjustments faster, at the " \ "expense of higher perf overhead. Time is in milliseconds.") \ \ product(bool, ShenandoahVerify, false, DIAGNOSTIC, \ "Enable internal verification. This would catch many GC bugs, " \ "but it would also stall the collector during the verification, " \ "which prolongs the pauses and might hide other bugs.") \ \ product(intx, ShenandoahVerifyLevel, 4, DIAGNOSTIC, \ "Verification level, higher levels check more, taking more time. "\ "Accepted values are:" \ " 0 = basic heap checks; " \ " 1 = previous level, plus basic region checks; " \ " 2 = previous level, plus all roots; " \ " 3 = previous level, plus all reachable objects; " \ " 4 = previous level, plus all marked objects") \ \ product(uintx, ShenandoahEvacReserve, 5, EXPERIMENTAL, \ "How much of (young-generation) heap to reserve for " \ "(young-generation) evacuations. Larger values allow GC to " \ "evacuate more live objects on every cycle, while leaving " \ "less headroom for application to allocate while GC is " \ "evacuating and updating references. This parameter is " \ "consulted at the end of marking, before selecting the " \ "collection set. If available memory at this time is smaller " \ "than the indicated reserve, the bound on collection set size is "\ "adjusted downward. The size of a generational mixed " \ "evacuation collection set (comprised of both young and old " \ "regions) is also bounded by this parameter. In percents of " \ "total (young-generation) heap size.") \ range(1,100) \ \ product(double, ShenandoahEvacWaste, 1.2, EXPERIMENTAL, \ "How much waste evacuations produce within the reserved space. " \ "Larger values make evacuations more resilient against " \ "evacuation conflicts, at expense of evacuating less on each " \ "GC cycle. Smaller values increase the risk of evacuation " \ "failures, which will trigger stop-the-world Full GC passes.") \ range(1.0,100.0) \ \ product(double, ShenandoahOldEvacWaste, 1.4, EXPERIMENTAL, \ "How much waste evacuations produce within the reserved space. " \ "Larger values make evacuations more resilient against " \ "evacuation conflicts, at expense of evacuating less on each " \ "GC cycle. Smaller values increase the risk of evacuation " \ "failures, which will trigger stop-the-world Full GC passes.") \ range(1.0,100.0) \ \ product(double, ShenandoahPromoEvacWaste, 1.2, EXPERIMENTAL, \ "How much waste promotions produce within the reserved space. " \ "Larger values make evacuations more resilient against " \ "evacuation conflicts, at expense of promoting less on each " \ "GC cycle. Smaller values increase the risk of evacuation " \ "failures, which will trigger stop-the-world Full GC passes.") \ range(1.0,100.0) \ \ product(bool, ShenandoahEvacReserveOverflow, true, EXPERIMENTAL, \ "Allow evacuations to overflow the reserved space. Enabling it " \ "will make evacuations more resilient when evacuation " \ "reserve/waste is incorrect, at the risk that application " \ "runs out of memory too early.") \ \ product(uintx, ShenandoahOldEvacRatioPercent, 75, EXPERIMENTAL, \ "The maximum proportion of evacuation from old-gen memory, " \ "expressed as a percentage. The default value 75 denotes that no" \ "more than 75% of the collection set evacuation workload may be " \ "towards evacuation of old-gen heap regions. This limits both the"\ "promotion of aged regions and the compaction of existing old " \ "regions. A value of 75 denotes that the total evacuation work" \ "may increase to up to four times the young gen evacuation work." \ "A larger value allows quicker promotion and allows" \ "a smaller number of mixed evacuations to process " \ "the entire list of old-gen collection candidates at the cost " \ "of an increased disruption of the normal cadence of young-gen " \ "collections. A value of 100 allows a mixed evacuation to " \ "focus entirely on old-gen memory, allowing no young-gen " \ "regions to be collected, likely resulting in subsequent " \ "allocation failures because the allocation pool is not " \ "replenished. A value of 0 allows a mixed evacuation to" \ "focus entirely on young-gen memory, allowing no old-gen " \ "regions to be collected, likely resulting in subsequent " \ "promotion failures and triggering of stop-the-world full GC " \ "events.") \ range(0,100) \ \ product(uintx, ShenandoahMinYoungPercentage, 20, EXPERIMENTAL, \ "The minimum percentage of the heap to use for the young " \ "generation. Heuristics will not adjust the young generation " \ "to be less than this.") \ range(0, 100) \ \ product(uintx, ShenandoahMaxYoungPercentage, 100, EXPERIMENTAL, \ "The maximum percentage of the heap to use for the young " \ "generation. Heuristics will not adjust the young generation " \ "to be more than this.") \ range(0, 100) \ \ product(bool, ShenandoahPacing, true, EXPERIMENTAL, \ "Pace application allocations to give GC chance to start " \ "and complete before allocation failure is reached.") \ \ product(uintx, ShenandoahPacingMaxDelay, 10, EXPERIMENTAL, \ "Max delay for pacing application allocations. Larger values " \ "provide more resilience against out of memory, at expense at " \ "hiding the GC latencies in the allocation path. Time is in " \ "milliseconds. Setting it to arbitrarily large value makes " \ "GC effectively stall the threads indefinitely instead of going " \ "to degenerated or Full GC.") \ \ product(uintx, ShenandoahPacingIdleSlack, 2, EXPERIMENTAL, \ "How much of heap counted as non-taxable allocations during idle "\ "phases. Larger value makes the pacing milder when collector is " \ "idle, requiring less rendezvous with control thread. Lower " \ "value makes the pacing control less responsive to out-of-cycle " \ "allocs. In percent of total heap size.") \ range(0, 100) \ \ product(uintx, ShenandoahPacingCycleSlack, 10, EXPERIMENTAL, \ "How much of free space to take as non-taxable allocations " \ "the GC cycle. Larger value makes the pacing milder at the " \ "beginning of the GC cycle. Lower value makes the pacing less " \ "uniform during the cycle. In percent of free space.") \ range(0, 100) \ \ product(double, ShenandoahPacingSurcharge, 1.1, EXPERIMENTAL, \ "Additional pacing tax surcharge to help unclutter the heap. " \ "Larger values makes the pacing more aggressive. Lower values " \ "risk GC cycles finish with less memory than were available at " \ "the beginning of it.") \ range(1.0, 100.0) \ \ product(uintx, ShenandoahCriticalFreeThreshold, 1, EXPERIMENTAL, \ "How much of the heap needs to be free after recovery cycles, " \ "either Degenerated or Full GC to be claimed successful. If this "\ "much space is not available, next recovery step would be " \ "triggered.") \ range(0, 100) \ \ product(bool, ShenandoahDegeneratedGC, true, DIAGNOSTIC, \ "Enable Degenerated GC as the graceful degradation step. " \ "Disabling this option leads to degradation to Full GC instead. " \ "When running in passive mode, this can be toggled to measure " \ "either Degenerated GC or Full GC costs.") \ \ product(uintx, ShenandoahFullGCThreshold, 3, EXPERIMENTAL, \ "How many back-to-back Degenerated GCs should happen before " \ "going to a Full GC.") \ \ product(uintx, ShenandoahNoProgressThreshold, 5, EXPERIMENTAL, \ "After this number of consecutive Full GCs fail to make " \ "progress, Shenandoah will raise out of memory errors. Note " \ "that progress is determined by ShenandoahCriticalFreeThreshold") \ \ product(bool, ShenandoahImplicitGCInvokesConcurrent, false, EXPERIMENTAL, \ "Should internally-caused GC requests invoke concurrent cycles, " \ "should they do the stop-the-world (Degenerated / Full GC)? " \ "Many heuristics automatically enable this. This option is " \ "similar to global ExplicitGCInvokesConcurrent.") \ \ product(bool, ShenandoahHumongousMoves, true, DIAGNOSTIC, \ "Allow moving humongous regions. This makes GC more resistant " \ "to external fragmentation that may otherwise fail other " \ "humongous allocations, at the expense of higher GC copying " \ "costs. Currently affects stop-the-world (Full) cycle only.") \ \ product(bool, ShenandoahOOMDuringEvacALot, false, DIAGNOSTIC, \ "Testing: simulate OOM during evacuation.") \ \ product(bool, ShenandoahAllocFailureALot, false, DIAGNOSTIC, \ "Testing: make lots of artificial allocation failures.") \ \ product(uintx, ShenandoahCoalesceChance, 0, DIAGNOSTIC, \ "Testing: Abandon remaining mixed collections with this " \ "likelihood. Following each mixed collection, abandon all " \ "remaining mixed collection candidate regions with likelihood " \ "ShenandoahCoalesceChance. Abandoning a mixed collection will " \ "cause the old regions to be made parsable, rather than being " \ "evacuated.") \ range(0, 100) \ \ product(intx, ShenandoahMarkScanPrefetch, 32, EXPERIMENTAL, \ "How many objects to prefetch ahead when traversing mark bitmaps."\ "Set to 0 to disable prefetching.") \ range(0, 256) \ \ product(uintx, ShenandoahMarkLoopStride, 1000, EXPERIMENTAL, \ "How many items to process during one marking iteration before " \ "checking for cancellation, yielding, etc. Larger values improve "\ "marking performance at expense of responsiveness.") \ \ product(uintx, ShenandoahParallelRegionStride, 0, EXPERIMENTAL, \ "How many regions to process at once during parallel region " \ "iteration. Affects heaps with lots of regions. " \ "Set to 0 to let Shenandoah to decide the best value.") \ \ product(size_t, ShenandoahSATBBufferSize, 1 * K, EXPERIMENTAL, \ "Number of entries in an SATB log buffer.") \ range(1, max_uintx) \ \ product(uintx, ShenandoahMaxSATBBufferFlushes, 5, EXPERIMENTAL, \ "How many times to maximum attempt to flush SATB buffers at the " \ "end of concurrent marking.") \ \ product(bool, ShenandoahSATBBarrier, true, DIAGNOSTIC, \ "Turn on/off SATB barriers in Shenandoah") \ \ product(bool, ShenandoahCardBarrier, false, DIAGNOSTIC, \ "Turn on/off card-marking post-write barrier in Shenandoah: " \ " true when ShenandoahGCMode is generational, false otherwise") \ \ product(bool, ShenandoahCASBarrier, true, DIAGNOSTIC, \ "Turn on/off CAS barriers in Shenandoah") \ \ product(bool, ShenandoahCloneBarrier, true, DIAGNOSTIC, \ "Turn on/off clone barriers in Shenandoah") \ \ product(bool, ShenandoahLoadRefBarrier, true, DIAGNOSTIC, \ "Turn on/off load-reference barriers in Shenandoah") \ \ product(bool, ShenandoahStackWatermarkBarrier, true, DIAGNOSTIC, \ "Turn on/off stack watermark barriers in Shenandoah") \ \ develop(bool, ShenandoahVerifyOptoBarriers, trueInDebug, \ "Verify no missing barriers in C2.") \ \ product(uintx, ShenandoahOldCompactionReserve, 8, EXPERIMENTAL, \ "During generational GC, prevent promotions from filling " \ "this number of heap regions. These regions are reserved " \ "for the purpose of supporting compaction of old-gen " \ "memory. Otherwise, old-gen memory cannot be compacted.") \ range(0, 128) \ \ product(bool, ShenandoahAllowOldMarkingPreemption, true, DIAGNOSTIC, \ "Allow young generation collections to suspend concurrent" \ " marking in the old generation.") \ \ product(uintx, ShenandoahAgingCyclePeriod, 1, EXPERIMENTAL, \ "With generational mode, increment the age of objects and" \ "regions each time this many young-gen GC cycles are completed.") \ \ develop(bool, ShenandoahEnableCardStats, false, \ "Enable statistics collection related to clean & dirty cards") \ \ develop(int, ShenandoahCardStatsLogInterval, 50, \ "Log cumulative card stats every so many remembered set or " \ "update refs scans") \ \ product(uintx, ShenandoahMinimumOldTimeMs, 100, EXPERIMENTAL, \ "Minimum amount of time in milliseconds to run old collections " \ "before a young collection is allowed to run. This is intended " \ "to prevent starvation of the old collector. Setting this to " \ "0 will allow back to back young collections to run during old " \ "collections.") \ // end of GC_SHENANDOAH_FLAGS #endif // SHARE_GC_SHENANDOAH_SHENANDOAH_GLOBALS_HPP