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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.

*** 32,10 ***
--- 33,90 ---
                              product_pd,                                     \
                              notproduct,                                     \
                              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 "   \

*** 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. "        \
--- 141,12 ---
    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. "        \

*** 74,29 ***
            " 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, 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, 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 "  \
--- 156,57 ---
            " 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 "  \

*** 108,16 ***
            "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)                                                      \
--- 218,16 ---
            "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)                                                      \

*** 142,23 ***
            "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.")                     \
                                                                              \
--- 252,43 ---
            "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.")                     \
                                                                              \

*** 214,29 ***
            " 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 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,                \
--- 344,89 ---
            " 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,                \

*** 284,10 ***
--- 474,15 ---
                                                                              \
    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.")                 \

*** 302,10 ***
--- 497,19 ---
            "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 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)                                                     \
                                                                              \

*** 330,10 ***
--- 534,14 ---
            "Turn on/off SATB barriers in Shenandoah")                        \
                                                                              \
    product(bool, ShenandoahIUBarrier, false, DIAGNOSTIC,                     \
            "Turn on/off I-U barriers 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")                       \

*** 345,9 ***
            "Turn on/off stack watermark barriers in Shenandoah")             \
                                                                              \
    develop(bool, ShenandoahVerifyOptoBarriers, trueInDebug,                  \
            "Verify no missing barriers in C2.")                              \
                                                                              \
! 
! // end of GC_SHENANDOAH_FLAGS
  
  #endif // SHARE_GC_SHENANDOAH_SHENANDOAH_GLOBALS_HPP
--- 553,36 ---
            "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.") \
+                                                                             \
+   notproduct(bool, ShenandoahEnableCardStats, false,                        \
+           "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")                                              \
+                                                                             \
+   product(uintx, ShenandoahMinimumOldMarkTimeMs, 100, EXPERIMENTAL,         \
+          "Minimum amount of time in milliseconds to run old marking "       \
+          "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 "   \
+          "marking.")                                                        \
+   // end of GC_SHENANDOAH_FLAGS
  
  #endif // SHARE_GC_SHENANDOAH_SHENANDOAH_GLOBALS_HPP
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