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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);" \
" iu - incremental-update concurrent GC (three pass mark-evac-update);" \
! " passive - stop the world GC only (either degenerated or full)") \
\
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. " \
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);" \
" iu - incremental-update 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. " \
" 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(ccstr, ShenandoahOldGCHeuristics, "adaptive", \
+ "Similar to ShenandoahGCHeuristics, but applied to the old " \
+ "generation. This configuration is only used to trigger old " \
+ "collections and does not change how regions are selected " \
+ "for collection.") \
+ \
product(uintx, ShenandoahUnloadClassesFrequency, 1, EXPERIMENTAL, \
"Unload the classes every Nth cycle. Normally affects concurrent "\
"GC cycles, as degenerated and full GCs would try to unload " \
"classes regardless. Set to zero to disable class unloading.") \
\
"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, ShenandoahInitFreeThreshold, 70, EXPERIMENTAL, \
! "How much heap should be free before some heuristics trigger the "\
! "initial (learning) cycles. Affects cycle frequency on startup " \
! "and after drastic state changes, e.g. after degenerated/full " \
! "GC cycles. In percents of (soft) max heap size.") \
range(0,100) \
\
product(uintx, ShenandoahMinFreeThreshold, 10, EXPERIMENTAL, \
! "How much heap should be free before most heuristics trigger the "\
! "collection, even without other triggers. Provides the 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 " \
"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, 25, EXPERIMENTAL, \
+ "How much garbage an old region has to contain before it would " \
+ "be taken for collection.") \
+ 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 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 " \
"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(bool, ShenandoahAdaptiveIgnoreShortCycles, true, EXPERIMENTAL, \
+ "The adaptive heuristic tracks a moving average of cycle " \
+ "times in order to start a gc before memory is exhausted. " \
+ "In some cases, Shenandoah may skip the evacuation and update " \
+ "reference phases, resulting in a shorter cycle. These may skew " \
+ "the average cycle time downward and may cause the heuristic " \
+ "to wait too long to start a cycle. Disabling this will have " \
+ "the gc run less often, which will reduce CPU utilization, but" \
+ "increase the risk of degenerated cycles.") \
+ \
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(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(bool, ShenandoahLogRegionSampling, false, \
+ "Save region sampling stream to ShenandoahRegionSamplingFile") \
+ \
+ product(ccstr, ShenandoahRegionSamplingFile, \
+ "./shenandoahSnapshots_pid%p.log", \
+ "If ShenandoahLogRegionSampling is on, save sampling data stream "\
+ "to this file [default: ./shenandoahSnapshots_pid%p.log] " \
+ "(%p replaced with pid)") \
+ \
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.") \
" 4 = previous level, plus all marked objects") \
\
product(bool, ShenandoahElasticTLAB, true, DIAGNOSTIC, \
"Use Elastic TLABs with Shenandoah") \
\
product(uintx, ShenandoahEvacReserve, 5, EXPERIMENTAL, \
! "How much of heap to reserve for evacuations. Larger values make "\
! "GC evacuate more live objects on every cycle, while leaving " \
! "less headroom for application to allocate in. In percents of " \
! "total 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.") \
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(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, \
" 4 = previous level, plus all marked objects") \
\
product(bool, ShenandoahElasticTLAB, true, DIAGNOSTIC, \
"Use Elastic TLABs with Shenandoah") \
\
+ product(bool, ShenandoahUsePLAB, true, DIAGNOSTIC, \
+ "Use PLABs for object promotions with Shenandoah, " \
+ "if in generational mode and UseTLAB is also set.") \
+ \
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 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, ShenandoahGenerationalEvacWaste, 2.0, EXPERIMENTAL, \
+ "For generational mode, 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. The default value for " \
+ "generational mode is 2.0. The reason for the higher default " \
+ "value in generational mode is because generational mode " \
+ "enforces the evacuation budget, triggering degenerated GC " \
+ "which upgrades to full GC whenever the budget is exceeded.") \
range(1.0,100.0) \
\
+ product(uintx, ShenandoahMaxEvacLABRatio, 16, EXPERIMENTAL, \
+ "Potentially, each running thread maintains a PLAB for " \
+ "evacuating objects into old-gen memory and a GCLAB for " \
+ "evacuating objects into young-gen memory. Each time a thread " \
+ "exhausts its PLAB or GCLAB, a new local buffer is allocated. " \
+ "By default, the new buffer is twice the size of the previous " \
+ "buffer. The sizes are reset to the minimum at the start of " \
+ "each GC pass. This parameter limits the growth of evacuation " \
+ "buffer sizes to its value multiplied by the minimum buffer " \
+ "size. A higher value allows evacuation allocations to be more " \
+ "efficient because less synchronization is required by " \
+ "individual threads. However, a larger value increases the " \
+ "likelihood of evacuation failures, leading to long " \
+ "stop-the-world pauses. This is because a large value " \
+ "allows individual threads to consume large percentages of " \
+ "the total evacuation budget without necessarily effectively " \
+ "filling their local evcauation buffers with evacuated " \
+ "objects. A value of zero means no maximum size is enforced.") \
+ range(0, 1024) \
+ \
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, ShenandoahOldEvacReserve, 2, EXPERIMENTAL, \
+ "How much of old-generation heap to reserve for old-generation " \
+ "evacuations. Larger values allow GC to evacuate more live " \
+ "old-generation objects on every cycle, while potentially " \
+ "creating greater impact on the cadence at which the young- " \
+ "generation allocation pool is replenished. During mixed " \
+ "evacuations, the bound on amount of old-generation heap " \
+ "regions included in the collecdtion set is the smaller " \
+ "of the quantities specified by this parameter and the " \
+ "size of ShenandoahEvacReserve as adjusted by the value of " \
+ "ShenandoahOldEvacRatioPercent. In percents of total " \
+ "old-generation heap size.") \
+ range(1,100) \
+ \
+ product(uintx, ShenandoahOldEvacRatioPercent, 12, EXPERIMENTAL, \
+ "The maximum proportion of evacuation from old-gen memory, as " \
+ "a percent ratio. The default value 12 denotes that no more " \
+ "than one eighth (12%) of the collection set evacuation " \
+ "workload may be comprised of old-gen heap regions. A larger " \
+ "value 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(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, \
product(bool, ShenandoahLoopOptsAfterExpansion, true, DIAGNOSTIC, \
"Attempt more loop opts after barrier expansion.") \
\
product(bool, ShenandoahSelfFixing, true, DIAGNOSTIC, \
"Fix references with load reference barrier. Disabling this " \
! "might degrade performance.")
!
! // end of GC_SHENANDOAH_FLAGS
#endif // SHARE_GC_SHENANDOAH_SHENANDOAH_GLOBALS_HPP
product(bool, ShenandoahLoopOptsAfterExpansion, true, DIAGNOSTIC, \
"Attempt more loop opts after barrier expansion.") \
\
product(bool, ShenandoahSelfFixing, true, DIAGNOSTIC, \
"Fix references with load reference barrier. Disabling this " \
! "might degrade performance.") \
! \
! product(uintx, ShenandoahTenuredRegionUsageBias, 16, EXPERIMENTAL, \
+ "The collection set is comprised of heap regions that contain " \
+ "the greatest amount of garbage. " \
+ "For purposes of selecting regions to be included in the " \
+ "collection set, regions that have reached the tenure age will " \
+ "be treated as if their contained garbage is the contained " \
+ "garbage multiplied by ShenandoahTenuredRegionUsageBias as " \
+ "many times as the age of the region meets or exceeds " \
+ "tenure age. For example, if tenure age is 7, " \
+ "the region age is 9, ShenandoahTenuredRegionUsageBias is " \
+ "16, and the region is 12.5% garbage, this region " \
+ "will by treated as if its garbage content is " \
+ "12.5% * 16 * 16 * 16 = 51,200% when comparing this region " \
+ " to untenured regions.") \
+ range(1,128) \
+ \
+ product(uintx, ShenandoahBorrowPercent, 30, EXPERIMENTAL, \
+ "During evacuation and reference updating in generational " \
+ "mode, new allocations are allowed to borrow from old-gen " \
+ "memory up to ShenandoahBorrowPercent / 100 amount of the " \
+ "young-generation content of the current collection set. " \
+ "Any memory borrowed from old-gen during evacuation and " \
+ "update-references phases of GC will be repaid from the " \
+ "abundance of young-gen memory produced when the collection " \
+ "set is recycled at the end of updating references. The " \
+ "default value of 30 reserves 70% of the to-be-reclaimed " \
+ "young collection set memory to be allocated during the " \
+ "subsequent concurrent mark phase of GC.") \
+ range(0, 100) \
+ \
+ product(bool, ShenandoahPromoteTenuredObjects, true, DIAGNOSTIC, \
+ "Turn on/off evacuating individual tenured young objects " \
+ " to the old generation.") \
+ \
+ 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.")
+ // end of GC_SHENANDOAH_FLAGS
#endif // SHARE_GC_SHENANDOAH_SHENANDOAH_GLOBALS_HPP
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