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src/hotspot/share/gc/shenandoah/shenandoah_globals.hpp

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*** 1,8 ***
  /*
!  * Copyright (c) 2020, Oracle and/or its affiliates. All rights reserved.
   * Copyright (c) 2016, 2021, Red Hat, Inc. 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.
--- 1,9 ---
  /*
!  * Copyright (c) 2020, 2023, 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.

*** 60,11 ***
    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. "        \
--- 61,12 ---
    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. "        \

*** 74,10 ***
--- 76,16 ---
            " 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", EXPERIMENTAL,       \
+           "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.")    \
                                                                              \

*** 87,21 ***
            "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 "  \
--- 95,39 ---
            "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 "  \

*** 113,16 ***
            "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, 90, 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)                                                      \
--- 139,16 ---
            "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, 10, 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)                                                      \

*** 147,23 ***
            "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(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.")                     \
                                                                              \
--- 173,43 ---
            "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, 0.1, 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(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.")                     \
                                                                              \

*** 219,32 ***
            " 2 = previous level, plus all roots; "                           \
            " 3 = previous level, plus all reachable objects; "               \
            " 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,                \
--- 265,113 ---
            " 2 = previous level, plus all roots; "                           \
            " 3 = previous level, plus all reachable objects; "               \
            " 4 = previous level, plus all marked objects")                   \
                                                                              \
    product(bool, ShenandoahElasticTLAB, true, DIAGNOSTIC,                    \
!           "Use Elastic TLABs with Shenandoah. This allows Shenandoah to "   \
+           "decrease the size of a TLAB to fit in a region's remaining space") \
                                                                              \
    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, 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(uintx, ShenandoahMaxEvacLABRatio, 0, 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 evacuation 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, ShenandoahOldEvacRatioPercent, 75, EXPERIMENTAL,           \
+           "The maximum proportion of evacuation from old-gen memory, as "   \
+           "a percent ratio.  The default value 75 denotes that no more "    \
+           "than 75% of the collection set evacuation "                      \
+           "workload may be evacuate to 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 normal "   \
+           "young-gen evacuation is increased by up to four fold. "          \
+           "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,                \

*** 288,14 ***
            "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(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.")                 \
--- 415,18 ---
            "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, 64, EXPERIMENTAL,               \
            "How many back-to-back Degenerated GCs should happen before "     \
            "going to a Full GC.")                                            \
                                                                              \
+   product(uintx, ShenandoahOOMGCRetries, 3, EXPERIMENTAL,                   \
+           "How many GCs should happen before we throw OutOfMemoryException "\
+           "for allocation request, including at least one Full GC.")        \
+                                                                             \
    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.")                 \

*** 310,10 ***
--- 441,19 ---
            "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 parseable, 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)                                                     \
                                                                              \

*** 364,10 ***
    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
--- 504,31 ---
    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, 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.") \
+                                                                             \
+   notproduct(bool, ShenandoahEnableCardStats, trueInDebug,                  \
+           "Enable statistics collection related to clean & dirty cards")    \
+                                                                             \
+   notproduct(int, ShenandoahCardStatsLogInterval, 50,                       \
+           "Log cumulative card stats every so many remembered set or "      \
+           "update refs scans")                                              \
+   // end of GC_SHENANDOAH_FLAGS
  
  #endif // SHARE_GC_SHENANDOAH_SHENANDOAH_GLOBALS_HPP
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