1 /*
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 13  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
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 26 
 27 #ifndef SHARE_GC_SHENANDOAH_SHENANDOAH_GLOBALS_HPP
 28 #define SHARE_GC_SHENANDOAH_SHENANDOAH_GLOBALS_HPP
 29 
 30 #define GC_SHENANDOAH_FLAGS(develop,                                        \
 31                             develop_pd,                                     \
 32                             product,                                        \
 33                             product_pd,                                     \
 34                             notproduct,                                     \
 35                             range,                                          \
 36                             constraint)                                     \
 37                                                                             \
 38   product(size_t, ShenandoahRegionSize, 0, EXPERIMENTAL,                    \
 39           "Static heap region size. Set zero to enable automatic sizing.")  \
 40                                                                             \
 41   product(size_t, ShenandoahTargetNumRegions, 2048, EXPERIMENTAL,           \
 42           "With automatic region sizing, this is the approximate number "   \
 43           "of regions that would be used, within min/max region size "      \
 44           "limits.")                                                        \
 45                                                                             \
 46   product(size_t, ShenandoahMinRegionSize, 256 * K, EXPERIMENTAL,           \
 47           "With automatic region sizing, the regions would be at least "    \
 48           "this large.")                                                    \
 49                                                                             \
 50   product(size_t, ShenandoahMaxRegionSize, 32 * M, EXPERIMENTAL,            \
 51           "With automatic region sizing, the regions would be at most "     \
 52           "this large.")                                                    \
 53                                                                             \
 54   product(intx, ShenandoahHumongousThreshold, 100, EXPERIMENTAL,            \
 55           "Humongous objects are allocated in separate regions. "           \
 56           "This setting defines how large the object should be to be "      \
 57           "deemed humongous. Value is in  percents of heap region size. "   \
 58           "This also caps the maximum TLAB size.")                          \
 59           range(1, 100)                                                     \
 60                                                                             \
 61   product(ccstr, ShenandoahGCMode, "satb",                                  \
 62           "GC mode to use.  Among other things, this defines which "        \
 63           "barriers are in in use. Possible values are:"                    \
 64           " satb - snapshot-at-the-beginning concurrent GC (three pass mark-evac-update);"  \
 65           " iu - incremental-update concurrent GC (three pass mark-evac-update);"  \
 66           " passive - stop the world GC only (either degenerated or full);" \
 67           " generational - generational concurrent GC")                     \
 68                                                                             \
 69   product(ccstr, ShenandoahGCHeuristics, "adaptive",                        \
 70           "GC heuristics to use. This fine-tunes the GC mode selected, "    \
 71           "by choosing when to start the GC, how much to process on each "  \
 72           "cycle, and what other features to automatically enable. "        \
 73           "Possible values are:"                                            \
 74           " adaptive - adapt to maintain the given amount of free heap "    \
 75           "at all times, even during the GC cycle;"                         \
 76           " static -  trigger GC when free heap falls below the threshold;" \
 77           " aggressive - run GC continuously, try to evacuate everything;"  \
 78           " compact - run GC more frequently and with deeper targets to "   \
 79           "free up more memory.")                                           \
 80                                                                             \
 81   product(ccstr, ShenandoahOldGCHeuristics, "adaptive", EXPERIMENTAL,       \
 82           "Similar to ShenandoahGCHeuristics, but applied to the old "      \
 83           "generation. This configuration is only used to trigger old "     \
 84           "collections and does not change how regions are selected "       \
 85           "for collection.")                                                \
 86                                                                             \
 87   product(uintx, ShenandoahUnloadClassesFrequency, 1, EXPERIMENTAL,         \
 88           "Unload the classes every Nth cycle. Normally affects concurrent "\
 89           "GC cycles, as degenerated and full GCs would try to unload "     \
 90           "classes regardless. Set to zero to disable class unloading.")    \
 91                                                                             \
 92   product(uintx, ShenandoahGarbageThreshold, 25, EXPERIMENTAL,              \
 93           "How much garbage a region has to contain before it would be "    \
 94           "taken for collection. This a guideline only, as GC heuristics "  \
 95           "may select the region for collection even if it has little "     \
 96           "garbage. This also affects how much internal fragmentation the " \
 97           "collector accepts. In percents of heap region size.")            \
 98           range(0,100)                                                      \
 99                                                                             \
100   product(uintx, ShenandoahOldGarbageThreshold, 15, EXPERIMENTAL,           \
101           "How much garbage an old region has to contain before it would "  \
102           "be taken for collection.")                                       \
103           range(0,100)                                                      \
104                                                                             \
105   product(uintx, ShenandoahIgnoreGarbageThreshold, 5, EXPERIMENTAL,         \
106           "When less than this amount of garbage (as a percentage of "      \
107           "region size) exists within a region, the region will not be "    \
108           "added to the collection set, even when the heuristic has "       \
109           "chosen to aggressively add regions with less than "              \
110           "ShenandoahGarbageThreshold amount of garbage into the "          \
111           "collection set.")                                                \
112           range(0,100)                                                      \
113                                                                             \
114   product(uintx, ShenandoahInitFreeThreshold, 70, EXPERIMENTAL,             \
115           "When less than this amount of memory is free within the"         \
116           "heap or generation, trigger a learning cycle if we are "         \
117           "in learning mode.  Learning mode happens during initialization " \
118           "and following a drastic state change, such as following a "      \
119           "degenerated or Full GC cycle.  In percents of soft max "         \
120           "heap size.")                                                     \
121           range(0,100)                                                      \
122                                                                             \
123   product(uintx, ShenandoahMinFreeThreshold, 10, EXPERIMENTAL,              \
124           "Percentage of free heap memory (or young generation, in "        \
125           "generational mode) below which most heuristics trigger "         \
126           "collection independent of other triggers. Provides a safety "    \
127           "margin for many heuristics. In percents of (soft) max heap "     \
128           "size.")                                                          \
129           range(0,100)                                                      \
130                                                                             \
131   product(uintx, ShenandoahAllocationThreshold, 0, EXPERIMENTAL,            \
132           "How many new allocations should happen since the last GC cycle " \
133           "before some heuristics trigger the collection. In percents of "  \
134           "(soft) max heap size. Set to zero to effectively disable.")      \
135           range(0,100)                                                      \
136                                                                             \
137   product(uintx, ShenandoahAllocSpikeFactor, 5, EXPERIMENTAL,               \
138           "How much of heap should some heuristics reserve for absorbing "  \
139           "the allocation spikes. Larger value wastes more memory in "      \
140           "non-emergency cases, but provides more safety in emergency "     \
141           "cases. In percents of (soft) max heap size.")                    \
142           range(0,100)                                                      \
143                                                                             \
144   product(uintx, ShenandoahLearningSteps, 10, EXPERIMENTAL,                 \
145           "The number of cycles some heuristics take to collect in order "  \
146           "to learn application and GC performance.")                       \
147           range(0,100)                                                      \
148                                                                             \
149   product(uintx, ShenandoahImmediateThreshold, 70, EXPERIMENTAL,            \
150           "The cycle may shortcut when enough garbage can be reclaimed "    \
151           "from the immediate garbage (completely garbage regions). "       \
152           "In percents of total garbage found. Setting this threshold "     \
153           "to 100 effectively disables the shortcut.")                      \
154           range(0,100)                                                      \
155                                                                             \
156   product(uintx, ShenandoahAdaptiveSampleFrequencyHz, 10, EXPERIMENTAL,     \
157           "The number of times per second to update the allocation rate "   \
158           "moving average.")                                                \
159                                                                             \
160   product(uintx, ShenandoahAdaptiveSampleSizeSeconds, 10, EXPERIMENTAL,     \
161           "The size of the moving window over which the average "           \
162           "allocation rate is maintained. The total number of samples "     \
163           "is the product of this number and the sample frequency.")        \
164                                                                             \
165   product(double, ShenandoahAdaptiveInitialConfidence, 1.8, EXPERIMENTAL,   \
166           "The number of standard deviations used to determine an initial " \
167           "margin of error for the average cycle time and average "         \
168           "allocation rate. Increasing this value will cause the "          \
169           "heuristic to initiate more concurrent cycles." )                 \
170                                                                             \
171   product(double, ShenandoahAdaptiveInitialSpikeThreshold, 1.8, EXPERIMENTAL, \
172           "If the most recently sampled allocation rate is more than "      \
173           "this many standard deviations away from the moving average, "    \
174           "then a cycle is initiated. This value controls how sensitive "   \
175           "the heuristic is to allocation spikes. Decreasing this number "  \
176           "increases the sensitivity. ")                                    \
177                                                                             \
178   product(double, ShenandoahAdaptiveDecayFactor, 0.1, EXPERIMENTAL,         \
179           "The decay factor (alpha) used for values in the weighted "       \
180           "moving average of cycle time and allocation rate. "              \
181           "Larger values give more weight to recent values.")               \
182           range(0,1.0)                                                      \
183                                                                             \
184   product(bool, ShenandoahAdaptiveIgnoreShortCycles, true, EXPERIMENTAL,    \
185           "The adaptive heuristic tracks a moving average of cycle "        \
186           "times in order to start a gc before memory is exhausted. "       \
187           "In some cases, Shenandoah may skip the evacuation and update "   \
188           "reference phases, resulting in a shorter cycle. These may skew " \
189           "the average cycle time downward and may cause the heuristic "    \
190           "to wait too long to start a cycle. Disabling this will have "    \
191           "the gc run less often, which will reduce CPU utilization, but"   \
192           "increase the risk of degenerated cycles.")                       \
193                                                                             \
194   product(uintx, ShenandoahGuaranteedGCInterval, 5*60*1000, EXPERIMENTAL,   \
195           "Many heuristics would guarantee a concurrent GC cycle at "       \
196           "least with this interval. This is useful when large idle "       \
197           "intervals are present, where GC can run without stealing "       \
198           "time from active application. Time is in milliseconds. "         \
199           "Setting this to 0 disables the feature.")                        \
200                                                                             \
201   product(uintx, ShenandoahGuaranteedOldGCInterval, 10*60*1000, EXPERIMENTAL, \
202           "Run a collection of the old generation at least this often. "    \
203           "Heuristics may trigger collections more frequently. Time is in " \
204           "milliseconds. Setting this to 0 disables the feature.")          \
205                                                                             \
206   product(uintx, ShenandoahGuaranteedYoungGCInterval, 5*60*1000,  EXPERIMENTAL,  \
207           "Run a collection of the young generation at least this often. "  \
208           "Heuristics may trigger collections more frequently. Time is in " \
209           "milliseconds. Setting this to 0 disables the feature.")          \
210                                                                             \
211   product(bool, ShenandoahAlwaysClearSoftRefs, false, EXPERIMENTAL,         \
212           "Unconditionally clear soft references, instead of using any "    \
213           "other cleanup policy. This minimizes footprint at expense of"    \
214           "more soft reference churn in applications.")                     \
215                                                                             \
216   product(bool, ShenandoahUncommit, true, EXPERIMENTAL,                     \
217           "Allow to uncommit memory under unused regions and metadata. "    \
218           "This optimizes footprint at expense of allocation latency in "   \
219           "regions that require committing back. Uncommits would be "       \
220           "disabled by some heuristics, or with static heap size.")         \
221                                                                             \
222   product(uintx, ShenandoahUncommitDelay, 5*60*1000, EXPERIMENTAL,          \
223           "Uncommit memory for regions that were not used for more than "   \
224           "this time. First use after that would incur allocation stalls. " \
225           "Actively used regions would never be uncommitted, because they " \
226           "do not become unused longer than this delay. Time is in "        \
227           "milliseconds. Setting this delay to 0 effectively uncommits "    \
228           "regions almost immediately after they become unused.")           \
229                                                                             \
230   product(bool, ShenandoahRegionSampling, false, EXPERIMENTAL,              \
231           "Provide heap region sampling data via jvmstat.")                 \
232                                                                             \
233   product(int, ShenandoahRegionSamplingRate, 40, EXPERIMENTAL,              \
234           "Sampling rate for heap region sampling. In milliseconds between "\
235           "the samples. Higher values provide more fidelity, at expense "   \
236           "of more sampling overhead.")                                     \
237                                                                             \
238   product(uintx, ShenandoahControlIntervalMin, 1, EXPERIMENTAL,             \
239           "The minimum sleep interval for the control loop that drives "    \
240           "the cycles. Lower values would increase GC responsiveness "      \
241           "to changing heap conditions, at the expense of higher perf "     \
242           "overhead. Time is in milliseconds.")                             \
243                                                                             \
244   product(uintx, ShenandoahControlIntervalMax, 10, EXPERIMENTAL,            \
245           "The maximum sleep interval for control loop that drives "        \
246           "the cycles. Lower values would increase GC responsiveness "      \
247           "to changing heap conditions, at the expense of higher perf "     \
248           "overhead. Time is in milliseconds.")                             \
249                                                                             \
250   product(uintx, ShenandoahControlIntervalAdjustPeriod, 1000, EXPERIMENTAL, \
251           "The time period for one step in control loop interval "          \
252           "adjustment. Lower values make adjustments faster, at the "       \
253           "expense of higher perf overhead. Time is in milliseconds.")      \
254                                                                             \
255   product(bool, ShenandoahVerify, false, DIAGNOSTIC,                        \
256           "Enable internal verification. This would catch many GC bugs, "   \
257           "but it would also stall the collector during the verification, " \
258           "which prolongs the pauses and might hide other bugs.")           \
259                                                                             \
260   product(intx, ShenandoahVerifyLevel, 4, DIAGNOSTIC,                       \
261           "Verification level, higher levels check more, taking more time. "\
262           "Accepted values are:"                                            \
263           " 0 = basic heap checks; "                                        \
264           " 1 = previous level, plus basic region checks; "                 \
265           " 2 = previous level, plus all roots; "                           \
266           " 3 = previous level, plus all reachable objects; "               \
267           " 4 = previous level, plus all marked objects")                   \
268                                                                             \
269   product(bool, ShenandoahElasticTLAB, true, DIAGNOSTIC,                    \
270           "Use Elastic TLABs with Shenandoah. This allows Shenandoah to "   \
271           "decrease the size of a TLAB to fit in a region's remaining space") \
272                                                                             \
273   product(uintx, ShenandoahEvacReserve, 5, EXPERIMENTAL,                    \
274           "How much of (young-generation) heap to reserve for "             \
275           "(young-generation) evacuations.  Larger values allow GC to "     \
276           "evacuate more live objects on every cycle, while leaving "       \
277           "less headroom for application to allocate while GC is "          \
278           "evacuating and updating references. This parameter is "          \
279           "consulted at the of marking, before selecting the collection "   \
280           "set.  If available memory at this time is smaller than the "     \
281           "indicated reserve, the bound on collection set size is "         \
282           "adjusted downward.  The size of a generational mixed "           \
283           "evacuation collection set (comprised of both young and old "     \
284           "regions) is also bounded by this parameter.  In percents of "    \
285           "total (young-generation) heap size.")                            \
286           range(1,100)                                                      \
287                                                                             \
288   product(double, ShenandoahEvacWaste, 1.2, EXPERIMENTAL,                   \
289           "How much waste evacuations produce within the reserved space. "  \
290           "Larger values make evacuations more resilient against "          \
291           "evacuation conflicts, at expense of evacuating less on each "    \
292           "GC cycle.  Smaller values increase the risk of evacuation "      \
293           "failures, which will trigger stop-the-world Full GC passes.")    \
294           range(1.0,100.0)                                                  \
295                                                                             \
296   product(double, ShenandoahOldEvacWaste, 1.4, EXPERIMENTAL,                \
297           "How much waste evacuations produce within the reserved space. "  \
298           "Larger values make evacuations more resilient against "          \
299           "evacuation conflicts, at expense of evacuating less on each "    \
300           "GC cycle.  Smaller values increase the risk of evacuation "      \
301           "failures, which will trigger stop-the-world Full GC passes.")    \
302           range(1.0,100.0)                                                  \
303                                                                             \
304   product(double, ShenandoahPromoEvacWaste, 1.2, EXPERIMENTAL,              \
305           "How much waste promotions produce within the reserved space. "   \
306           "Larger values make evacuations more resilient against "          \
307           "evacuation conflicts, at expense of promoting less on each "     \
308           "GC cycle.  Smaller values increase the risk of evacuation "      \
309           "failures, which will trigger stop-the-world Full GC passes.")    \
310           range(1.0,100.0)                                                  \
311                                                                             \
312   product(uintx, ShenandoahMaxEvacLABRatio, 0, EXPERIMENTAL,                \
313           "Potentially, each running thread maintains a PLAB for "          \
314           "evacuating objects into old-gen memory and a GCLAB for "         \
315           "evacuating objects into young-gen memory.  Each time a thread "  \
316           "exhausts its PLAB or GCLAB, a new local buffer is allocated. "   \
317           "By default, the new buffer is twice the size of the previous "   \
318           "buffer.  The sizes are reset to the minimum at the start of "    \
319           "each GC pass.  This parameter limits the growth of evacuation "  \
320           "buffer sizes to its value multiplied by the minimum buffer "     \
321           "size.  A higher value allows evacuation allocations to be more " \
322           "efficient because less synchronization is required by "          \
323           "individual threads.  However, a larger value increases the "     \
324           "likelihood of evacuation failures, leading to long "             \
325           "stop-the-world pauses.  This is because a large value "          \
326           "allows individual threads to consume large percentages of "      \
327           "the total evacuation budget without necessarily effectively "    \
328           "filling their local evacuation buffers with evacuated "          \
329           "objects.  A value of zero means no maximum size is enforced.")   \
330           range(0, 1024)                                                    \
331                                                                             \
332   product(bool, ShenandoahEvacReserveOverflow, true, EXPERIMENTAL,          \
333           "Allow evacuations to overflow the reserved space. Enabling it "  \
334           "will make evacuations more resilient when evacuation "           \
335           "reserve/waste is incorrect, at the risk that application "       \
336           "runs out of memory too early.")                                  \
337                                                                             \
338   product(uintx, ShenandoahOldEvacRatioPercent, 75, EXPERIMENTAL,           \
339           "The maximum proportion of evacuation from old-gen memory, as "   \
340           "a percent ratio.  The default value 75 denotes that no more "    \
341           "than 75% of the collection set evacuation "                      \
342           "workload may be evacuate to old-gen heap regions.  This limits " \
343           "both the promotion of aged regions and the compaction of "       \
344           "existing old regions.  A value of 75 denotes that the normal "   \
345           "young-gen evacuation is increased by up to four fold. "          \
346           "A larger value allows quicker promotion and allows"              \
347           "a smaller number of mixed evacuations to process "               \
348           "the entire list of old-gen collection candidates at the cost "   \
349           "of an increased disruption of the normal cadence of young-gen "  \
350           "collections.  A value of 100 allows a mixed evacuation to "      \
351           "focus entirely on old-gen memory, allowing no young-gen "        \
352           "regions to be collected, likely resulting in subsequent "        \
353           "allocation failures because the allocation pool is not "         \
354           "replenished.  A value of 0 allows a mixed evacuation to"         \
355           "focus entirely on young-gen memory, allowing no old-gen "        \
356           "regions to be collected, likely resulting in subsequent "        \
357           "promotion failures and triggering of stop-the-world full GC "    \
358           "events.")                                                        \
359           range(0,100)                                                      \
360                                                                             \
361   product(uintx, ShenandoahMinYoungPercentage, 20, EXPERIMENTAL,            \
362           "The minimum percentage of the heap to use for the young "        \
363           "generation. Heuristics will not adjust the young generation "    \
364           "to be less than this.")                                          \
365           range(0, 100)                                                     \
366                                                                             \
367   product(uintx, ShenandoahMaxYoungPercentage, 100, EXPERIMENTAL,           \
368           "The maximum percentage of the heap to use for the young "        \
369           "generation. Heuristics will not adjust the young generation "    \
370           "to be more than this.")                                          \
371           range(0, 100)                                                     \
372                                                                             \
373   product(bool, ShenandoahPacing, true, EXPERIMENTAL,                       \
374           "Pace application allocations to give GC chance to start "        \
375           "and complete before allocation failure is reached.")             \
376                                                                             \
377   product(uintx, ShenandoahPacingMaxDelay, 10, EXPERIMENTAL,                \
378           "Max delay for pacing application allocations. Larger values "    \
379           "provide more resilience against out of memory, at expense at "   \
380           "hiding the GC latencies in the allocation path. Time is in "     \
381           "milliseconds. Setting it to arbitrarily large value makes "      \
382           "GC effectively stall the threads indefinitely instead of going " \
383           "to degenerated or Full GC.")                                     \
384                                                                             \
385   product(uintx, ShenandoahPacingIdleSlack, 2, EXPERIMENTAL,                \
386           "How much of heap counted as non-taxable allocations during idle "\
387           "phases. Larger value makes the pacing milder when collector is " \
388           "idle, requiring less rendezvous with control thread. Lower "     \
389           "value makes the pacing control less responsive to out-of-cycle " \
390           "allocs. In percent of total heap size.")                         \
391           range(0, 100)                                                     \
392                                                                             \
393   product(uintx, ShenandoahPacingCycleSlack, 10, EXPERIMENTAL,              \
394           "How much of free space to take as non-taxable allocations "      \
395           "the GC cycle. Larger value makes the pacing milder at the "      \
396           "beginning of the GC cycle. Lower value makes the pacing less "   \
397           "uniform during the cycle. In percent of free space.")            \
398           range(0, 100)                                                     \
399                                                                             \
400   product(double, ShenandoahPacingSurcharge, 1.1, EXPERIMENTAL,             \
401           "Additional pacing tax surcharge to help unclutter the heap. "    \
402           "Larger values makes the pacing more aggressive. Lower values "   \
403           "risk GC cycles finish with less memory than were available at "  \
404           "the beginning of it.")                                           \
405           range(1.0, 100.0)                                                 \
406                                                                             \
407   product(uintx, ShenandoahCriticalFreeThreshold, 1, EXPERIMENTAL,          \
408           "How much of the heap needs to be free after recovery cycles, "   \
409           "either Degenerated or Full GC to be claimed successful. If this "\
410           "much space is not available, next recovery step would be "       \
411           "triggered.")                                                     \
412           range(0, 100)                                                     \
413                                                                             \
414   product(bool, ShenandoahDegeneratedGC, true, DIAGNOSTIC,                  \
415           "Enable Degenerated GC as the graceful degradation step. "        \
416           "Disabling this option leads to degradation to Full GC instead. " \
417           "When running in passive mode, this can be toggled to measure "   \
418           "either Degenerated GC or Full GC costs.")                        \
419                                                                             \
420   product(uintx, ShenandoahFullGCThreshold, 64, EXPERIMENTAL,               \
421           "How many back-to-back Degenerated GCs should happen before "     \
422           "going to a Full GC.")                                            \
423                                                                             \
424   product(uintx, ShenandoahOOMGCRetries, 3, EXPERIMENTAL,                   \
425           "How many GCs should happen before we throw OutOfMemoryException "\
426           "for allocation request, including at least one Full GC.")        \
427                                                                             \
428   product(bool, ShenandoahImplicitGCInvokesConcurrent, false, EXPERIMENTAL, \
429           "Should internally-caused GC requests invoke concurrent cycles, " \
430           "should they do the stop-the-world (Degenerated / Full GC)? "     \
431           "Many heuristics automatically enable this. This option is "      \
432           "similar to global ExplicitGCInvokesConcurrent.")                 \
433                                                                             \
434   product(bool, ShenandoahHumongousMoves, true, DIAGNOSTIC,                 \
435           "Allow moving humongous regions. This makes GC more resistant "   \
436           "to external fragmentation that may otherwise fail other "        \
437           "humongous allocations, at the expense of higher GC copying "     \
438           "costs. Currently affects stop-the-world (Full) cycle only.")     \
439                                                                             \
440   product(bool, ShenandoahOOMDuringEvacALot, false, DIAGNOSTIC,             \
441           "Testing: simulate OOM during evacuation.")                       \
442                                                                             \
443   product(bool, ShenandoahAllocFailureALot, false, DIAGNOSTIC,              \
444           "Testing: make lots of artificial allocation failures.")          \
445                                                                             \
446   product(uintx, ShenandoahCoalesceChance, 0, DIAGNOSTIC,                   \
447           "Testing: Abandon remaining mixed collections with this "         \
448           "likelihood. Following each mixed collection, abandon all "       \
449           "remaining mixed collection candidate regions with likelihood "   \
450           "ShenandoahCoalesceChance. Abandoning a mixed collection will "   \
451           "cause the old regions to be made parseable, rather than being "  \
452           "evacuated.")                                                     \
453           range(0, 100)                                                     \
454                                                                             \
455   product(intx, ShenandoahMarkScanPrefetch, 32, EXPERIMENTAL,               \
456           "How many objects to prefetch ahead when traversing mark bitmaps."\
457           "Set to 0 to disable prefetching.")                               \
458           range(0, 256)                                                     \
459                                                                             \
460   product(uintx, ShenandoahMarkLoopStride, 1000, EXPERIMENTAL,              \
461           "How many items to process during one marking iteration before "  \
462           "checking for cancellation, yielding, etc. Larger values improve "\
463           "marking performance at expense of responsiveness.")              \
464                                                                             \
465   product(uintx, ShenandoahParallelRegionStride, 1024, EXPERIMENTAL,        \
466           "How many regions to process at once during parallel region "     \
467           "iteration. Affects heaps with lots of regions.")                 \
468                                                                             \
469   product(size_t, ShenandoahSATBBufferSize, 1 * K, EXPERIMENTAL,            \
470           "Number of entries in an SATB log buffer.")                       \
471           range(1, max_uintx)                                               \
472                                                                             \
473   product(uintx, ShenandoahMaxSATBBufferFlushes, 5, EXPERIMENTAL,           \
474           "How many times to maximum attempt to flush SATB buffers at the " \
475           "end of concurrent marking.")                                     \
476                                                                             \
477   product(bool, ShenandoahSuspendibleWorkers, true, EXPERIMENTAL,           \
478           "Suspend concurrent GC worker threads at safepoints")             \
479                                                                             \
480   product(bool, ShenandoahSATBBarrier, true, DIAGNOSTIC,                    \
481           "Turn on/off SATB barriers in Shenandoah")                        \
482                                                                             \
483   product(bool, ShenandoahIUBarrier, false, DIAGNOSTIC,                     \
484           "Turn on/off I-U barriers barriers in Shenandoah")                \
485                                                                             \
486   product(bool, ShenandoahCASBarrier, true, DIAGNOSTIC,                     \
487           "Turn on/off CAS barriers in Shenandoah")                         \
488                                                                             \
489   product(bool, ShenandoahCloneBarrier, true, DIAGNOSTIC,                   \
490           "Turn on/off clone barriers in Shenandoah")                       \
491                                                                             \
492   product(bool, ShenandoahLoadRefBarrier, true, DIAGNOSTIC,                 \
493           "Turn on/off load-reference barriers in Shenandoah")              \
494                                                                             \
495   product(bool, ShenandoahNMethodBarrier, true, DIAGNOSTIC,                 \
496           "Turn on/off NMethod entry barriers in Shenandoah")               \
497                                                                             \
498   product(bool, ShenandoahStackWatermarkBarrier, true, DIAGNOSTIC,          \
499           "Turn on/off stack watermark barriers in Shenandoah")             \
500                                                                             \
501   develop(bool, ShenandoahVerifyOptoBarriers, false,                        \
502           "Verify no missing barriers in C2.")                              \
503                                                                             \
504   product(bool, ShenandoahLoopOptsAfterExpansion, true, DIAGNOSTIC,         \
505           "Attempt more loop opts after barrier expansion.")                \
506                                                                             \
507   product(bool, ShenandoahSelfFixing, true, DIAGNOSTIC,                     \
508           "Fix references with load reference barrier. Disabling this "     \
509           "might degrade performance.")                                     \
510                                                                             \
511   product(uintx, ShenandoahOldCompactionReserve, 8, EXPERIMENTAL,           \
512           "During generational GC, prevent promotions from filling "        \
513           "this number of heap regions.  These regions are reserved "       \
514           "for the purpose of supporting compaction of old-gen "            \
515           "memory.  Otherwise, old-gen memory cannot be compacted.")        \
516           range(0, 128)                                                     \
517                                                                             \
518   product(bool, ShenandoahAllowOldMarkingPreemption, true, DIAGNOSTIC,      \
519           "Allow young generation collections to suspend concurrent"        \
520           " marking in the old generation.")                                \
521                                                                             \
522   product(uintx, ShenandoahAgingCyclePeriod, 1, EXPERIMENTAL,               \
523           "With generational mode, increment the age of objects and"        \
524           "regions each time this many young-gen GC cycles are completed.") \
525                                                                             \
526   notproduct(bool, ShenandoahEnableCardStats, trueInDebug,                  \
527           "Enable statistics collection related to clean & dirty cards")    \
528                                                                             \
529   notproduct(int, ShenandoahCardStatsLogInterval, 50,                       \
530           "Log cumulative card stats every so many remembered set or "      \
531           "update refs scans")                                              \
532   // end of GC_SHENANDOAH_FLAGS
533 
534 #endif // SHARE_GC_SHENANDOAH_SHENANDOAH_GLOBALS_HPP