1 /*
  2  * Copyright (c) 2020, Oracle and/or its affiliates. All rights reserved.
  3  * Copyright (c) 2016, 2021, Red Hat, Inc. All rights reserved.

  4  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  5  *
  6  * This code is free software; you can redistribute it and/or modify it
  7  * under the terms of the GNU General Public License version 2 only, as
  8  * published by the Free Software Foundation.
  9  *
 10  * This code is distributed in the hope that it will be useful, but WITHOUT
 11  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 12  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 13  * version 2 for more details (a copy is included in the LICENSE file that
 14  * accompanied this code).
 15  *
 16  * You should have received a copy of the GNU General Public License version
 17  * 2 along with this work; if not, write to the Free Software Foundation,
 18  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 19  *
 20  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
 21  * or visit www.oracle.com if you need additional information or have any
 22  * questions.
 23  *
 24  */
 25 
 26 #ifndef SHARE_GC_SHENANDOAH_SHENANDOAH_GLOBALS_HPP
 27 #define SHARE_GC_SHENANDOAH_SHENANDOAH_GLOBALS_HPP
 28 
 29 #define GC_SHENANDOAH_FLAGS(develop,                                        \
 30                             develop_pd,                                     \
 31                             product,                                        \
 32                             product_pd,                                     \
 33                             notproduct,                                     \
 34                             range,                                          \
 35                             constraint)                                     \
 36                                                                             \
















































































 37   product(size_t, ShenandoahRegionSize, 0, EXPERIMENTAL,                    \
 38           "Static heap region size. Set zero to enable automatic sizing.")  \
 39                                                                             \
 40   product(size_t, ShenandoahTargetNumRegions, 2048, EXPERIMENTAL,           \
 41           "With automatic region sizing, this is the approximate number "   \
 42           "of regions that would be used, within min/max region size "      \
 43           "limits.")                                                        \
 44                                                                             \
 45   product(size_t, ShenandoahMinRegionSize, 256 * K, EXPERIMENTAL,           \
 46           "With automatic region sizing, the regions would be at least "    \
 47           "this large.")                                                    \
 48                                                                             \
 49   product(size_t, ShenandoahMaxRegionSize, 32 * M, EXPERIMENTAL,            \
 50           "With automatic region sizing, the regions would be at most "     \
 51           "this large.")                                                    \
 52                                                                             \
 53   product(intx, ShenandoahHumongousThreshold, 100, EXPERIMENTAL,            \
 54           "Humongous objects are allocated in separate regions. "           \
 55           "This setting defines how large the object should be to be "      \
 56           "deemed humongous. Value is in  percents of heap region size. "   \
 57           "This also caps the maximum TLAB size.")                          \
 58           range(1, 100)                                                     \
 59                                                                             \
 60   product(ccstr, ShenandoahGCMode, "satb",                                  \
 61           "GC mode to use.  Among other things, this defines which "        \
 62           "barriers are in in use. Possible values are:"                    \
 63           " satb - snapshot-at-the-beginning concurrent GC (three pass mark-evac-update);"  \
 64           " iu - incremental-update concurrent GC (three pass mark-evac-update);"  \
 65           " passive - stop the world GC only (either degenerated or full)") \

 66                                                                             \
 67   product(ccstr, ShenandoahGCHeuristics, "adaptive",                        \
 68           "GC heuristics to use. This fine-tunes the GC mode selected, "    \
 69           "by choosing when to start the GC, how much to process on each "  \
 70           "cycle, and what other features to automatically enable. "        \
 71           "Possible values are:"                                            \
 72           " adaptive - adapt to maintain the given amount of free heap "    \
 73           "at all times, even during the GC cycle;"                         \
 74           " static -  trigger GC when free heap falls below the threshold;" \
 75           " aggressive - run GC continuously, try to evacuate everything;"  \
 76           " compact - run GC more frequently and with deeper targets to "   \
 77           "free up more memory.")                                           \
 78                                                                             \










 79   product(uintx, ShenandoahGarbageThreshold, 25, EXPERIMENTAL,              \
 80           "How much garbage a region has to contain before it would be "    \
 81           "taken for collection. This a guideline only, as GC heuristics "  \
 82           "may select the region for collection even if it has little "     \
 83           "garbage. This also affects how much internal fragmentation the " \
 84           "collector accepts. In percents of heap region size.")            \
 85           range(0,100)                                                      \
 86                                                                             \














 87   product(uintx, ShenandoahInitFreeThreshold, 70, EXPERIMENTAL,             \
 88           "How much heap should be free before some heuristics trigger the "\
 89           "initial (learning) cycles. Affects cycle frequency on startup "  \
 90           "and after drastic state changes, e.g. after degenerated/full "   \
 91           "GC cycles. In percents of (soft) max heap size.")                \


 92           range(0,100)                                                      \
 93                                                                             \
 94   product(uintx, ShenandoahMinFreeThreshold, 10, EXPERIMENTAL,              \
 95           "How much heap should be free before most heuristics trigger the "\
 96           "collection, even without other triggers. Provides the safety "   \
 97           "margin for many heuristics. In percents of (soft) max heap size.")\


 98           range(0,100)                                                      \
 99                                                                             \
100   product(uintx, ShenandoahAllocationThreshold, 0, EXPERIMENTAL,            \
101           "How many new allocations should happen since the last GC cycle " \
102           "before some heuristics trigger the collection. In percents of "  \
103           "(soft) max heap size. Set to zero to effectively disable.")      \
104           range(0,100)                                                      \
105                                                                             \
106   product(uintx, ShenandoahAllocSpikeFactor, 5, EXPERIMENTAL,               \
107           "How much of heap should some heuristics reserve for absorbing "  \
108           "the allocation spikes. Larger value wastes more memory in "      \
109           "non-emergency cases, but provides more safety in emergency "     \
110           "cases. In percents of (soft) max heap size.")                    \
111           range(0,100)                                                      \
112                                                                             \
113   product(uintx, ShenandoahLearningSteps, 5, EXPERIMENTAL,                  \
114           "The number of cycles some heuristics take to collect in order "  \
115           "to learn application and GC performance.")                       \
116           range(0,100)                                                      \
117                                                                             \
118   product(uintx, ShenandoahImmediateThreshold, 90, EXPERIMENTAL,            \
119           "The cycle may shortcut when enough garbage can be reclaimed "    \
120           "from the immediate garbage (completely garbage regions). "       \
121           "In percents of total garbage found. Setting this threshold "     \
122           "to 100 effectively disables the shortcut.")                      \
123           range(0,100)                                                      \
124                                                                             \
125   product(uintx, ShenandoahAdaptiveSampleFrequencyHz, 10, EXPERIMENTAL,     \
126           "The number of times per second to update the allocation rate "   \
127           "moving average.")                                                \
128                                                                             \
129   product(uintx, ShenandoahAdaptiveSampleSizeSeconds, 10, EXPERIMENTAL,     \
130           "The size of the moving window over which the average "           \
131           "allocation rate is maintained. The total number of samples "     \
132           "is the product of this number and the sample frequency.")        \
133                                                                             \
134   product(double, ShenandoahAdaptiveInitialConfidence, 1.8, EXPERIMENTAL,   \
135           "The number of standard deviations used to determine an initial " \
136           "margin of error for the average cycle time and average "         \
137           "allocation rate. Increasing this value will cause the "          \
138           "heuristic to initiate more concurrent cycles." )                 \
139                                                                             \
140   product(double, ShenandoahAdaptiveInitialSpikeThreshold, 1.8, EXPERIMENTAL, \
141           "If the most recently sampled allocation rate is more than "      \
142           "this many standard deviations away from the moving average, "    \
143           "then a cycle is initiated. This value controls how sensitive "   \
144           "the heuristic is to allocation spikes. Decreasing this number "  \
145           "increases the sensitivity. ")                                    \
146                                                                             \
147   product(double, ShenandoahAdaptiveDecayFactor, 0.5, EXPERIMENTAL,         \
148           "The decay factor (alpha) used for values in the weighted "       \
149           "moving average of cycle time and allocation rate. "              \
150           "Larger values give more weight to recent values.")               \
151           range(0,1.0)                                                      \
152                                                                             \










153   product(uintx, ShenandoahGuaranteedGCInterval, 5*60*1000, EXPERIMENTAL,   \
154           "Many heuristics would guarantee a concurrent GC cycle at "       \
155           "least with this interval. This is useful when large idle "       \
156           "intervals are present, where GC can run without stealing "       \
157           "time from active application. Time is in milliseconds. "         \
158           "Setting this to 0 disables the feature.")                        \
159                                                                             \










160   product(bool, ShenandoahAlwaysClearSoftRefs, false, EXPERIMENTAL,         \
161           "Unconditionally clear soft references, instead of using any "    \
162           "other cleanup policy. This minimizes footprint at expense of"    \
163           "more soft reference churn in applications.")                     \
164                                                                             \
165   product(bool, ShenandoahUncommit, true, EXPERIMENTAL,                     \
166           "Allow to uncommit memory under unused regions and metadata. "    \
167           "This optimizes footprint at expense of allocation latency in "   \
168           "regions that require committing back. Uncommits would be "       \
169           "disabled by some heuristics, or with static heap size.")         \
170                                                                             \
171   product(uintx, ShenandoahUncommitDelay, 5*60*1000, EXPERIMENTAL,          \
172           "Uncommit memory for regions that were not used for more than "   \
173           "this time. First use after that would incur allocation stalls. " \
174           "Actively used regions would never be uncommitted, because they " \
175           "do not become unused longer than this delay. Time is in "        \
176           "milliseconds. Setting this delay to 0 effectively uncommits "    \
177           "regions almost immediately after they become unused.")           \
178                                                                             \
179   product(bool, ShenandoahRegionSampling, false, EXPERIMENTAL,              \
180           "Provide heap region sampling data via jvmstat.")                 \
181                                                                             \
182   product(int, ShenandoahRegionSamplingRate, 40, EXPERIMENTAL,              \
183           "Sampling rate for heap region sampling. In milliseconds between "\
184           "the samples. Higher values provide more fidelity, at expense "   \
185           "of more sampling overhead.")                                     \
186                                                                             \
187   product(uintx, ShenandoahControlIntervalMin, 1, EXPERIMENTAL,             \
188           "The minimum sleep interval for the control loop that drives "    \
189           "the cycles. Lower values would increase GC responsiveness "      \
190           "to changing heap conditions, at the expense of higher perf "     \
191           "overhead. Time is in milliseconds.")                             \
192                                                                             \
193   product(uintx, ShenandoahControlIntervalMax, 10, EXPERIMENTAL,            \
194           "The maximum sleep interval for control loop that drives "        \
195           "the cycles. Lower values would increase GC responsiveness "      \
196           "to changing heap conditions, at the expense of higher perf "     \
197           "overhead. Time is in milliseconds.")                             \
198                                                                             \
199   product(uintx, ShenandoahControlIntervalAdjustPeriod, 1000, EXPERIMENTAL, \
200           "The time period for one step in control loop interval "          \
201           "adjustment. Lower values make adjustments faster, at the "       \
202           "expense of higher perf overhead. Time is in milliseconds.")      \
203                                                                             \
204   product(bool, ShenandoahVerify, false, DIAGNOSTIC,                        \
205           "Enable internal verification. This would catch many GC bugs, "   \
206           "but it would also stall the collector during the verification, " \
207           "which prolongs the pauses and might hide other bugs.")           \
208                                                                             \
209   product(intx, ShenandoahVerifyLevel, 4, DIAGNOSTIC,                       \
210           "Verification level, higher levels check more, taking more time. "\
211           "Accepted values are:"                                            \
212           " 0 = basic heap checks; "                                        \
213           " 1 = previous level, plus basic region checks; "                 \
214           " 2 = previous level, plus all roots; "                           \
215           " 3 = previous level, plus all reachable objects; "               \
216           " 4 = previous level, plus all marked objects")                   \
217                                                                             \
218   product(uintx, ShenandoahEvacReserve, 5, EXPERIMENTAL,                    \
219           "How much of heap to reserve for evacuations. Larger values make "\
220           "GC evacuate more live objects on every cycle, while leaving "    \
221           "less headroom for application to allocate in. In percents of "   \
222           "total heap size.")                                               \








223           range(1,100)                                                      \
224                                                                             \
225   product(double, ShenandoahEvacWaste, 1.2, EXPERIMENTAL,                   \
226           "How much waste evacuations produce within the reserved space. "  \
227           "Larger values make evacuations more resilient against "          \
228           "evacuation conflicts, at expense of evacuating less on each "    \
229           "GC cycle.")                                                      \

230           range(1.0,100.0)                                                  \
231                                                                             \




































232   product(bool, ShenandoahEvacReserveOverflow, true, EXPERIMENTAL,          \
233           "Allow evacuations to overflow the reserved space. Enabling it "  \
234           "will make evacuations more resilient when evacuation "           \
235           "reserve/waste is incorrect, at the risk that application "       \
236           "runs out of memory too early.")                                  \
237                                                                             \



































238   product(bool, ShenandoahPacing, true, EXPERIMENTAL,                       \
239           "Pace application allocations to give GC chance to start "        \
240           "and complete before allocation failure is reached.")             \
241                                                                             \
242   product(uintx, ShenandoahPacingMaxDelay, 10, EXPERIMENTAL,                \
243           "Max delay for pacing application allocations. Larger values "    \
244           "provide more resilience against out of memory, at expense at "   \
245           "hiding the GC latencies in the allocation path. Time is in "     \
246           "milliseconds. Setting it to arbitrarily large value makes "      \
247           "GC effectively stall the threads indefinitely instead of going " \
248           "to degenerated or Full GC.")                                     \
249                                                                             \
250   product(uintx, ShenandoahPacingIdleSlack, 2, EXPERIMENTAL,                \
251           "How much of heap counted as non-taxable allocations during idle "\
252           "phases. Larger value makes the pacing milder when collector is " \
253           "idle, requiring less rendezvous with control thread. Lower "     \
254           "value makes the pacing control less responsive to out-of-cycle " \
255           "allocs. In percent of total heap size.")                         \
256           range(0, 100)                                                     \
257                                                                             \
258   product(uintx, ShenandoahPacingCycleSlack, 10, EXPERIMENTAL,              \
259           "How much of free space to take as non-taxable allocations "      \
260           "the GC cycle. Larger value makes the pacing milder at the "      \
261           "beginning of the GC cycle. Lower value makes the pacing less "   \
262           "uniform during the cycle. In percent of free space.")            \
263           range(0, 100)                                                     \
264                                                                             \
265   product(double, ShenandoahPacingSurcharge, 1.1, EXPERIMENTAL,             \
266           "Additional pacing tax surcharge to help unclutter the heap. "    \
267           "Larger values makes the pacing more aggressive. Lower values "   \
268           "risk GC cycles finish with less memory than were available at "  \
269           "the beginning of it.")                                           \
270           range(1.0, 100.0)                                                 \
271                                                                             \
272   product(uintx, ShenandoahCriticalFreeThreshold, 1, EXPERIMENTAL,          \
273           "How much of the heap needs to be free after recovery cycles, "   \
274           "either Degenerated or Full GC to be claimed successful. If this "\
275           "much space is not available, next recovery step would be "       \
276           "triggered.")                                                     \
277           range(0, 100)                                                     \
278                                                                             \
279   product(bool, ShenandoahDegeneratedGC, true, DIAGNOSTIC,                  \
280           "Enable Degenerated GC as the graceful degradation step. "        \
281           "Disabling this option leads to degradation to Full GC instead. " \
282           "When running in passive mode, this can be toggled to measure "   \
283           "either Degenerated GC or Full GC costs.")                        \
284                                                                             \
285   product(uintx, ShenandoahFullGCThreshold, 3, EXPERIMENTAL,                \
286           "How many back-to-back Degenerated GCs should happen before "     \
287           "going to a Full GC.")                                            \
288                                                                             \





289   product(bool, ShenandoahImplicitGCInvokesConcurrent, false, EXPERIMENTAL, \
290           "Should internally-caused GC requests invoke concurrent cycles, " \
291           "should they do the stop-the-world (Degenerated / Full GC)? "     \
292           "Many heuristics automatically enable this. This option is "      \
293           "similar to global ExplicitGCInvokesConcurrent.")                 \
294                                                                             \
295   product(bool, ShenandoahHumongousMoves, true, DIAGNOSTIC,                 \
296           "Allow moving humongous regions. This makes GC more resistant "   \
297           "to external fragmentation that may otherwise fail other "        \
298           "humongous allocations, at the expense of higher GC copying "     \
299           "costs. Currently affects stop-the-world (Full) cycle only.")     \
300                                                                             \
301   product(bool, ShenandoahOOMDuringEvacALot, false, DIAGNOSTIC,             \
302           "Testing: simulate OOM during evacuation.")                       \
303                                                                             \
304   product(bool, ShenandoahAllocFailureALot, false, DIAGNOSTIC,              \
305           "Testing: make lots of artificial allocation failures.")          \
306                                                                             \









307   product(intx, ShenandoahMarkScanPrefetch, 32, EXPERIMENTAL,               \
308           "How many objects to prefetch ahead when traversing mark bitmaps."\
309           "Set to 0 to disable prefetching.")                               \
310           range(0, 256)                                                     \
311                                                                             \
312   product(uintx, ShenandoahMarkLoopStride, 1000, EXPERIMENTAL,              \
313           "How many items to process during one marking iteration before "  \
314           "checking for cancellation, yielding, etc. Larger values improve "\
315           "marking performance at expense of responsiveness.")              \
316                                                                             \
317   product(uintx, ShenandoahParallelRegionStride, 1024, EXPERIMENTAL,        \
318           "How many regions to process at once during parallel region "     \
319           "iteration. Affects heaps with lots of regions.")                 \
320                                                                             \
321   product(size_t, ShenandoahSATBBufferSize, 1 * K, EXPERIMENTAL,            \
322           "Number of entries in an SATB log buffer.")                       \
323           range(1, max_uintx)                                               \
324                                                                             \
325   product(uintx, ShenandoahMaxSATBBufferFlushes, 5, EXPERIMENTAL,           \
326           "How many times to maximum attempt to flush SATB buffers at the " \
327           "end of concurrent marking.")                                     \
328                                                                             \
329   product(bool, ShenandoahSATBBarrier, true, DIAGNOSTIC,                    \
330           "Turn on/off SATB barriers in Shenandoah")                        \
331                                                                             \
332   product(bool, ShenandoahIUBarrier, false, DIAGNOSTIC,                     \
333           "Turn on/off I-U barriers barriers in Shenandoah")                \
334                                                                             \




335   product(bool, ShenandoahCASBarrier, true, DIAGNOSTIC,                     \
336           "Turn on/off CAS barriers in Shenandoah")                         \
337                                                                             \
338   product(bool, ShenandoahCloneBarrier, true, DIAGNOSTIC,                   \
339           "Turn on/off clone barriers in Shenandoah")                       \
340                                                                             \
341   product(bool, ShenandoahLoadRefBarrier, true, DIAGNOSTIC,                 \
342           "Turn on/off load-reference barriers in Shenandoah")              \
343                                                                             \
344   product(bool, ShenandoahStackWatermarkBarrier, true, DIAGNOSTIC,          \
345           "Turn on/off stack watermark barriers in Shenandoah")             \
346                                                                             \
347   develop(bool, ShenandoahVerifyOptoBarriers, trueInDebug,                  \
348           "Verify no missing barriers in C2.")                              \
349                                                                             \
350 
351 // end of GC_SHENANDOAH_FLAGS



























352 
353 #endif // SHARE_GC_SHENANDOAH_SHENANDOAH_GLOBALS_HPP
--- EOF ---