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

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@@ -60,11 +60,12 @@
    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)") \
+           " 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 +75,16 @@
            " 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",                     \
+           "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 +94,29 @@
            "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,             \
-           "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.")                \
+           "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,              \
-           "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.")\
+           "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 "  \

@@ -153,17 +168,37 @@
            "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.")                     \
                                                                              \

@@ -187,10 +222,19 @@
    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.")                             \

@@ -221,30 +265,109 @@
            " 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 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.")                                               \
+           "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.")                                                      \
+           "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,                \

@@ -364,10 +487,51 @@
    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
+           "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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