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, ShenandoahUnloadClassesFrequency, 1, EXPERIMENTAL, \
80 "Unload the classes every Nth cycle. Normally affects concurrent "\
81 "GC cycles, as degenerated and full GCs would try to unload " \
82 "classes regardless. Set to zero to disable class unloading.") \
83 \
84 product(uintx, ShenandoahGarbageThreshold, 25, EXPERIMENTAL, \
85 "How much garbage a region has to contain before it would be " \
86 "taken for collection. This a guideline only, as GC heuristics " \
87 "may select the region for collection even if it has little " \
88 "garbage. This also affects how much internal fragmentation the " \
89 "collector accepts. In percents of heap region size.") \
90 range(0,100) \
91 \
92 product(uintx, ShenandoahInitFreeThreshold, 70, EXPERIMENTAL, \
93 "How much heap should be free before some heuristics trigger the "\
94 "initial (learning) cycles. Affects cycle frequency on startup " \
95 "and after drastic state changes, e.g. after degenerated/full " \
96 "GC cycles. In percents of (soft) max heap size.") \
97 range(0,100) \
98 \
99 product(uintx, ShenandoahMinFreeThreshold, 10, EXPERIMENTAL, \
100 "How much heap should be free before most heuristics trigger the "\
101 "collection, even without other triggers. Provides the safety " \
102 "margin for many heuristics. In percents of (soft) max heap size.")\
103 range(0,100) \
104 \
105 product(uintx, ShenandoahAllocationThreshold, 0, EXPERIMENTAL, \
106 "How many new allocations should happen since the last GC cycle " \
107 "before some heuristics trigger the collection. In percents of " \
108 "(soft) max heap size. Set to zero to effectively disable.") \
109 range(0,100) \
110 \
111 product(uintx, ShenandoahAllocSpikeFactor, 5, EXPERIMENTAL, \
112 "How much of heap should some heuristics reserve for absorbing " \
113 "the allocation spikes. Larger value wastes more memory in " \
114 "non-emergency cases, but provides more safety in emergency " \
115 "cases. In percents of (soft) max heap size.") \
116 range(0,100) \
117 \
118 product(uintx, ShenandoahLearningSteps, 5, EXPERIMENTAL, \
119 "The number of cycles some heuristics take to collect in order " \
120 "to learn application and GC performance.") \
121 range(0,100) \
122 \
123 product(uintx, ShenandoahImmediateThreshold, 90, EXPERIMENTAL, \
124 "The cycle may shortcut when enough garbage can be reclaimed " \
125 "from the immediate garbage (completely garbage regions). " \
126 "In percents of total garbage found. Setting this threshold " \
127 "to 100 effectively disables the shortcut.") \
128 range(0,100) \
129 \
130 product(uintx, ShenandoahAdaptiveSampleFrequencyHz, 10, EXPERIMENTAL, \
131 "The number of times per second to update the allocation rate " \
132 "moving average.") \
133 \
134 product(uintx, ShenandoahAdaptiveSampleSizeSeconds, 10, EXPERIMENTAL, \
135 "The size of the moving window over which the average " \
136 "allocation rate is maintained. The total number of samples " \
137 "is the product of this number and the sample frequency.") \
138 \
139 product(double, ShenandoahAdaptiveInitialConfidence, 1.8, EXPERIMENTAL, \
140 "The number of standard deviations used to determine an initial " \
141 "margin of error for the average cycle time and average " \
142 "allocation rate. Increasing this value will cause the " \
143 "heuristic to initiate more concurrent cycles." ) \
144 \
145 product(double, ShenandoahAdaptiveInitialSpikeThreshold, 1.8, EXPERIMENTAL, \
146 "If the most recently sampled allocation rate is more than " \
147 "this many standard deviations away from the moving average, " \
148 "then a cycle is initiated. This value controls how sensitive " \
149 "the heuristic is to allocation spikes. Decreasing this number " \
150 "increases the sensitivity. ") \
151 \
152 product(double, ShenandoahAdaptiveDecayFactor, 0.5, EXPERIMENTAL, \
153 "The decay factor (alpha) used for values in the weighted " \
154 "moving average of cycle time and allocation rate. " \
155 "Larger values give more weight to recent values.") \
156 range(0,1.0) \
157 \
158 product(uintx, ShenandoahGuaranteedGCInterval, 5*60*1000, EXPERIMENTAL, \
159 "Many heuristics would guarantee a concurrent GC cycle at " \
160 "least with this interval. This is useful when large idle " \
161 "intervals are present, where GC can run without stealing " \
162 "time from active application. Time is in milliseconds. " \
163 "Setting this to 0 disables the feature.") \
164 \
165 product(bool, ShenandoahAlwaysClearSoftRefs, false, EXPERIMENTAL, \
166 "Unconditionally clear soft references, instead of using any " \
167 "other cleanup policy. This minimizes footprint at expense of" \
168 "more soft reference churn in applications.") \
169 \
170 product(bool, ShenandoahUncommit, true, EXPERIMENTAL, \
171 "Allow to uncommit memory under unused regions and metadata. " \
172 "This optimizes footprint at expense of allocation latency in " \
173 "regions that require committing back. Uncommits would be " \
174 "disabled by some heuristics, or with static heap size.") \
175 \
176 product(uintx, ShenandoahUncommitDelay, 5*60*1000, EXPERIMENTAL, \
177 "Uncommit memory for regions that were not used for more than " \
178 "this time. First use after that would incur allocation stalls. " \
179 "Actively used regions would never be uncommitted, because they " \
180 "do not become unused longer than this delay. Time is in " \
181 "milliseconds. Setting this delay to 0 effectively uncommits " \
182 "regions almost immediately after they become unused.") \
183 \
184 product(bool, ShenandoahRegionSampling, false, EXPERIMENTAL, \
204 product(uintx, ShenandoahControlIntervalAdjustPeriod, 1000, EXPERIMENTAL, \
205 "The time period for one step in control loop interval " \
206 "adjustment. Lower values make adjustments faster, at the " \
207 "expense of higher perf overhead. Time is in milliseconds.") \
208 \
209 product(bool, ShenandoahVerify, false, DIAGNOSTIC, \
210 "Enable internal verification. This would catch many GC bugs, " \
211 "but it would also stall the collector during the verification, " \
212 "which prolongs the pauses and might hide other bugs.") \
213 \
214 product(intx, ShenandoahVerifyLevel, 4, DIAGNOSTIC, \
215 "Verification level, higher levels check more, taking more time. "\
216 "Accepted values are:" \
217 " 0 = basic heap checks; " \
218 " 1 = previous level, plus basic region checks; " \
219 " 2 = previous level, plus all roots; " \
220 " 3 = previous level, plus all reachable objects; " \
221 " 4 = previous level, plus all marked objects") \
222 \
223 product(bool, ShenandoahElasticTLAB, true, DIAGNOSTIC, \
224 "Use Elastic TLABs with Shenandoah") \
225 \
226 product(uintx, ShenandoahEvacReserve, 5, EXPERIMENTAL, \
227 "How much of heap to reserve for evacuations. Larger values make "\
228 "GC evacuate more live objects on every cycle, while leaving " \
229 "less headroom for application to allocate in. In percents of " \
230 "total heap size.") \
231 range(1,100) \
232 \
233 product(double, ShenandoahEvacWaste, 1.2, EXPERIMENTAL, \
234 "How much waste evacuations produce within the reserved space. " \
235 "Larger values make evacuations more resilient against " \
236 "evacuation conflicts, at expense of evacuating less on each " \
237 "GC cycle.") \
238 range(1.0,100.0) \
239 \
240 product(bool, ShenandoahEvacReserveOverflow, true, EXPERIMENTAL, \
241 "Allow evacuations to overflow the reserved space. Enabling it " \
242 "will make evacuations more resilient when evacuation " \
243 "reserve/waste is incorrect, at the risk that application " \
244 "runs out of memory too early.") \
245 \
246 product(bool, ShenandoahPacing, true, EXPERIMENTAL, \
247 "Pace application allocations to give GC chance to start " \
248 "and complete before allocation failure is reached.") \
249 \
250 product(uintx, ShenandoahPacingMaxDelay, 10, EXPERIMENTAL, \
251 "Max delay for pacing application allocations. Larger values " \
252 "provide more resilience against out of memory, at expense at " \
253 "hiding the GC latencies in the allocation path. Time is in " \
254 "milliseconds. Setting it to arbitrarily large value makes " \
255 "GC effectively stall the threads indefinitely instead of going " \
256 "to degenerated or Full GC.") \
257 \
258 product(uintx, ShenandoahPacingIdleSlack, 2, EXPERIMENTAL, \
259 "How much of heap counted as non-taxable allocations during idle "\
260 "phases. Larger value makes the pacing milder when collector is " \
261 "idle, requiring less rendezvous with control thread. Lower " \
262 "value makes the pacing control less responsive to out-of-cycle " \
263 "allocs. In percent of total heap size.") \
264 range(0, 100) \
265 \
300 "that progress is determined by ShenandoahCriticalFreeThreshold") \
301 \
302 product(bool, ShenandoahImplicitGCInvokesConcurrent, false, EXPERIMENTAL, \
303 "Should internally-caused GC requests invoke concurrent cycles, " \
304 "should they do the stop-the-world (Degenerated / Full GC)? " \
305 "Many heuristics automatically enable this. This option is " \
306 "similar to global ExplicitGCInvokesConcurrent.") \
307 \
308 product(bool, ShenandoahHumongousMoves, true, DIAGNOSTIC, \
309 "Allow moving humongous regions. This makes GC more resistant " \
310 "to external fragmentation that may otherwise fail other " \
311 "humongous allocations, at the expense of higher GC copying " \
312 "costs. Currently affects stop-the-world (Full) cycle only.") \
313 \
314 product(bool, ShenandoahOOMDuringEvacALot, false, DIAGNOSTIC, \
315 "Testing: simulate OOM during evacuation.") \
316 \
317 product(bool, ShenandoahAllocFailureALot, false, DIAGNOSTIC, \
318 "Testing: make lots of artificial allocation failures.") \
319 \
320 product(intx, ShenandoahMarkScanPrefetch, 32, EXPERIMENTAL, \
321 "How many objects to prefetch ahead when traversing mark bitmaps."\
322 "Set to 0 to disable prefetching.") \
323 range(0, 256) \
324 \
325 product(uintx, ShenandoahMarkLoopStride, 1000, EXPERIMENTAL, \
326 "How many items to process during one marking iteration before " \
327 "checking for cancellation, yielding, etc. Larger values improve "\
328 "marking performance at expense of responsiveness.") \
329 \
330 product(uintx, ShenandoahParallelRegionStride, 1024, EXPERIMENTAL, \
331 "How many regions to process at once during parallel region " \
332 "iteration. Affects heaps with lots of regions.") \
333 \
334 product(size_t, ShenandoahSATBBufferSize, 1 * K, EXPERIMENTAL, \
335 "Number of entries in an SATB log buffer.") \
336 range(1, max_uintx) \
337 \
338 product(uintx, ShenandoahMaxSATBBufferFlushes, 5, EXPERIMENTAL, \
339 "How many times to maximum attempt to flush SATB buffers at the " \
340 "end of concurrent marking.") \
341 \
342 product(bool, ShenandoahSuspendibleWorkers, true, EXPERIMENTAL, \
343 "Suspend concurrent GC worker threads at safepoints") \
344 \
345 product(bool, ShenandoahSATBBarrier, true, DIAGNOSTIC, \
346 "Turn on/off SATB barriers in Shenandoah") \
347 \
348 product(bool, ShenandoahIUBarrier, false, DIAGNOSTIC, \
349 "Turn on/off I-U barriers barriers in Shenandoah") \
350 \
351 product(bool, ShenandoahCASBarrier, true, DIAGNOSTIC, \
352 "Turn on/off CAS barriers in Shenandoah") \
353 \
354 product(bool, ShenandoahCloneBarrier, true, DIAGNOSTIC, \
355 "Turn on/off clone barriers in Shenandoah") \
356 \
357 product(bool, ShenandoahLoadRefBarrier, true, DIAGNOSTIC, \
358 "Turn on/off load-reference barriers in Shenandoah") \
359 \
360 product(bool, ShenandoahStackWatermarkBarrier, true, DIAGNOSTIC, \
361 "Turn on/off stack watermark barriers in Shenandoah") \
362 \
363 develop(bool, ShenandoahVerifyOptoBarriers, false, \
364 "Verify no missing barriers in C2.") \
365 \
366 product(bool, ShenandoahLoopOptsAfterExpansion, true, DIAGNOSTIC, \
367 "Attempt more loop opts after barrier expansion.") \
368 \
369 product(bool, ShenandoahSelfFixing, true, DIAGNOSTIC, \
370 "Fix references with load reference barrier. Disabling this " \
371 "might degrade performance.")
372
373 // end of GC_SHENANDOAH_FLAGS
374
375 #endif // SHARE_GC_SHENANDOAH_SHENANDOAH_GLOBALS_HPP
|
1 /*
2 * Copyright (c) 2020, 2023, Oracle and/or its affiliates. All rights reserved.
3 * Copyright (c) 2016, 2021, Red Hat, Inc. All rights reserved.
4 * Copyright Amazon.com Inc. or its affiliates. All Rights Reserved.
5 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
6 *
7 * This code is free software; you can redistribute it and/or modify it
8 * under the terms of the GNU General Public License version 2 only, as
9 * published by the Free Software Foundation.
10 *
11 * This code is distributed in the hope that it will be useful, but WITHOUT
12 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
13 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
14 * version 2 for more details (a copy is included in the LICENSE file that
15 * accompanied this code).
16 *
17 * You should have received a copy of the GNU General Public License version
18 * 2 along with this work; if not, write to the Free Software Foundation,
19 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
20 *
21 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
22 * or visit www.oracle.com if you need additional information or have any
23 * questions.
24 *
25 */
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(uintx, ShenandoahGenerationalHumongousReserve, 0, EXPERIMENTAL, \
39 "(Generational mode only) What percent of the heap should be " \
40 "reserved for humongous objects if possible. Old-generation " \
41 "collections will endeavor to evacuate old-gen regions within " \
42 "this reserved area even if these regions do not contain high " \
43 "percentage of garbage. Setting a larger value will cause " \
44 "more frequent old-gen collections. A smaller value will " \
45 "increase the likelihood that humongous object allocations " \
46 "fail, resulting in stop-the-world full GCs.") \
47 range(0,100) \
48 \
49 product(double, ShenandoahMinOldGenGrowthPercent, 12.5, EXPERIMENTAL, \
50 "(Generational mode only) If the usage within old generation " \
51 "has grown by at least this percent of its live memory size " \
52 "at completion of the most recent old-generation marking " \
53 "effort, heuristics may trigger the start of a new old-gen " \
54 "collection.") \
55 range(0.0,100.0) \
56 \
57 product(uintx, ShenandoahIgnoreOldGrowthBelowPercentage,10, EXPERIMENTAL, \
58 "(Generational mode only) If the total usage of the old " \
59 "generation is smaller than this percent, we do not trigger " \
60 "old gen collections even if old has grown, except when " \
61 "ShenandoahGenerationalDoNotIgnoreGrowthAfterYoungCycles " \
62 "consecutive cycles have been completed following the " \
63 "preceding old-gen collection.") \
64 range(0,100) \
65 \
66 product(uintx, ShenandoahDoNotIgnoreGrowthAfterYoungCycles, \
67 50, EXPERIMENTAL, \
68 "(Generational mode only) Even if the usage of old generation " \
69 "is below ShenandoahIgnoreOldGrowthBelowPercentage, " \
70 "trigger an old-generation mark if old has grown and this " \
71 "many consecutive young-gen collections have been " \
72 "completed following the preceding old-gen collection.") \
73 \
74 product(bool, ShenandoahGenerationalCensusAtEvac, false, EXPERIMENTAL, \
75 "(Generational mode only) Object age census at evacuation, " \
76 "rather than during marking.") \
77 \
78 product(bool, ShenandoahGenerationalAdaptiveTenuring, true, EXPERIMENTAL, \
79 "(Generational mode only) Dynamically adapt tenuring age.") \
80 \
81 product(bool, ShenandoahGenerationalCensusIgnoreOlderCohorts, true, \
82 EXPERIMENTAL,\
83 "(Generational mode only) Ignore mortality rates older than the " \
84 "oldest cohort under the tenuring age for the last cycle." ) \
85 \
86 product(uintx, ShenandoahGenerationalMinTenuringAge, 1, EXPERIMENTAL, \
87 "(Generational mode only) Floor for adaptive tenuring age. " \
88 "Setting floor and ceiling to the same value fixes the tenuring " \
89 "age; setting both to 1 simulates a poor approximation to " \
90 "AlwaysTenure, and setting both to 16 simulates NeverTenure.") \
91 range(1,16) \
92 \
93 product(uintx, ShenandoahGenerationalMaxTenuringAge, 15, EXPERIMENTAL, \
94 "(Generational mode only) Ceiling for adaptive tenuring age. " \
95 "Setting floor and ceiling to the same value fixes the tenuring " \
96 "age; setting both to 1 simulates a poor approximation to " \
97 "AlwaysTenure, and setting both to 16 simulates NeverTenure.") \
98 range(1,16) \
99 \
100 product(double, ShenandoahGenerationalTenuringMortalityRateThreshold, \
101 0.1, EXPERIMENTAL, \
102 "(Generational mode only) Cohort mortality rates below this " \
103 "value will be treated as indicative of longevity, leading to " \
104 "tenuring. A lower value delays tenuring, a higher value hastens "\
105 "it. Used only when ShenandoahGenerationalhenAdaptiveTenuring is "\
106 "enabled.") \
107 range(0.001,0.999) \
108 \
109 product(size_t, ShenandoahGenerationalTenuringCohortPopulationThreshold, \
110 4*K, EXPERIMENTAL, \
111 "(Generational mode only) Cohorts whose population is lower than "\
112 "this value in the previous census are ignored wrt tenuring " \
113 "decisions. Effectively this makes then tenurable as soon as all "\
114 "older cohorts are. Set this value to the largest cohort " \
115 "population volume that you are comfortable ignoring when making "\
116 "tenuring decisions.") \
117 \
118 product(size_t, ShenandoahRegionSize, 0, EXPERIMENTAL, \
119 "Static heap region size. Set zero to enable automatic sizing.") \
120 \
121 product(size_t, ShenandoahTargetNumRegions, 2048, EXPERIMENTAL, \
122 "With automatic region sizing, this is the approximate number " \
123 "of regions that would be used, within min/max region size " \
124 "limits.") \
125 \
126 product(size_t, ShenandoahMinRegionSize, 256 * K, EXPERIMENTAL, \
127 "With automatic region sizing, the regions would be at least " \
128 "this large.") \
129 \
130 product(size_t, ShenandoahMaxRegionSize, 32 * M, EXPERIMENTAL, \
131 "With automatic region sizing, the regions would be at most " \
132 "this large.") \
133 \
134 product(intx, ShenandoahHumongousThreshold, 100, EXPERIMENTAL, \
135 "Humongous objects are allocated in separate regions. " \
136 "This setting defines how large the object should be to be " \
137 "deemed humongous. Value is in percents of heap region size. " \
138 "This also caps the maximum TLAB size.") \
139 range(1, 100) \
140 \
141 product(ccstr, ShenandoahGCMode, "satb", \
142 "GC mode to use. Among other things, this defines which " \
143 "barriers are in in use. Possible values are:" \
144 " satb - snapshot-at-the-beginning concurrent GC (three pass mark-evac-update);" \
145 " iu - incremental-update concurrent GC (three pass mark-evac-update);" \
146 " passive - stop the world GC only (either degenerated or full);" \
147 " generational - generational concurrent GC") \
148 \
149 product(ccstr, ShenandoahGCHeuristics, "adaptive", \
150 "GC heuristics to use. This fine-tunes the GC mode selected, " \
151 "by choosing when to start the GC, how much to process on each " \
152 "cycle, and what other features to automatically enable. " \
153 "Possible values are:" \
154 " adaptive - adapt to maintain the given amount of free heap " \
155 "at all times, even during the GC cycle;" \
156 " static - trigger GC when free heap falls below the threshold;" \
157 " aggressive - run GC continuously, try to evacuate everything;" \
158 " compact - run GC more frequently and with deeper targets to " \
159 "free up more memory.") \
160 \
161 product(uintx, ShenandoahExpeditePromotionsThreshold, 5, EXPERIMENTAL, \
162 "When Shenandoah expects to promote at least this percentage " \
163 "of the young generation, trigger a young collection to " \
164 "expedite these promotions.") \
165 range(0,100) \
166 \
167 product(uintx, ShenandoahExpediteMixedThreshold, 10, EXPERIMENTAL, \
168 "When there are this many old regions waiting to be collected, " \
169 "trigger a mixed collection immediately.") \
170 \
171 product(uintx, ShenandoahUnloadClassesFrequency, 1, EXPERIMENTAL, \
172 "Unload the classes every Nth cycle. Normally affects concurrent "\
173 "GC cycles, as degenerated and full GCs would try to unload " \
174 "classes regardless. Set to zero to disable class unloading.") \
175 \
176 product(uintx, ShenandoahGarbageThreshold, 25, EXPERIMENTAL, \
177 "How much garbage a region has to contain before it would be " \
178 "taken for collection. This a guideline only, as GC heuristics " \
179 "may select the region for collection even if it has little " \
180 "garbage. This also affects how much internal fragmentation the " \
181 "collector accepts. In percents of heap region size.") \
182 range(0,100) \
183 \
184 product(uintx, ShenandoahOldGarbageThreshold, 15, EXPERIMENTAL, \
185 "How much garbage an old region has to contain before it would " \
186 "be taken for collection.") \
187 range(0,100) \
188 \
189 product(uintx, ShenandoahIgnoreGarbageThreshold, 5, EXPERIMENTAL, \
190 "When less than this amount of garbage (as a percentage of " \
191 "region size) exists within a region, the region will not be " \
192 "added to the collection set, even when the heuristic has " \
193 "chosen to aggressively add regions with less than " \
194 "ShenandoahGarbageThreshold amount of garbage into the " \
195 "collection set.") \
196 range(0,100) \
197 \
198 product(uintx, ShenandoahInitFreeThreshold, 70, EXPERIMENTAL, \
199 "When less than this amount of memory is free within the" \
200 "heap or generation, trigger a learning cycle if we are " \
201 "in learning mode. Learning mode happens during initialization " \
202 "and following a drastic state change, such as following a " \
203 "degenerated or Full GC cycle. In percents of soft max " \
204 "heap size.") \
205 range(0,100) \
206 \
207 product(uintx, ShenandoahMinFreeThreshold, 10, EXPERIMENTAL, \
208 "Percentage of free heap memory (or young generation, in " \
209 "generational mode) below which most heuristics trigger " \
210 "collection independent of other triggers. Provides a safety " \
211 "margin for many heuristics. In percents of (soft) max heap " \
212 "size.") \
213 range(0,100) \
214 \
215 product(uintx, ShenandoahAllocationThreshold, 0, EXPERIMENTAL, \
216 "How many new allocations should happen since the last GC cycle " \
217 "before some heuristics trigger the collection. In percents of " \
218 "(soft) max heap size. Set to zero to effectively disable.") \
219 range(0,100) \
220 \
221 product(uintx, ShenandoahAllocSpikeFactor, 5, EXPERIMENTAL, \
222 "How much of heap should some heuristics reserve for absorbing " \
223 "the allocation spikes. Larger value wastes more memory in " \
224 "non-emergency cases, but provides more safety in emergency " \
225 "cases. In percents of (soft) max heap size.") \
226 range(0,100) \
227 \
228 product(uintx, ShenandoahLearningSteps, 10, EXPERIMENTAL, \
229 "The number of cycles some heuristics take to collect in order " \
230 "to learn application and GC performance.") \
231 range(0,100) \
232 \
233 product(uintx, ShenandoahImmediateThreshold, 70, EXPERIMENTAL, \
234 "The cycle may shortcut when enough garbage can be reclaimed " \
235 "from the immediate garbage (completely garbage regions). " \
236 "In percents of total garbage found. Setting this threshold " \
237 "to 100 effectively disables the shortcut.") \
238 range(0,100) \
239 \
240 product(uintx, ShenandoahAdaptiveSampleFrequencyHz, 10, EXPERIMENTAL, \
241 "The number of times per second to update the allocation rate " \
242 "moving average.") \
243 \
244 product(uintx, ShenandoahAdaptiveSampleSizeSeconds, 10, EXPERIMENTAL, \
245 "The size of the moving window over which the average " \
246 "allocation rate is maintained. The total number of samples " \
247 "is the product of this number and the sample frequency.") \
248 \
249 product(double, ShenandoahAdaptiveInitialConfidence, 1.8, EXPERIMENTAL, \
250 "The number of standard deviations used to determine an initial " \
251 "margin of error for the average cycle time and average " \
252 "allocation rate. Increasing this value will cause the " \
253 "heuristic to initiate more concurrent cycles." ) \
254 \
255 product(double, ShenandoahAdaptiveInitialSpikeThreshold, 1.8, EXPERIMENTAL, \
256 "If the most recently sampled allocation rate is more than " \
257 "this many standard deviations away from the moving average, " \
258 "then a cycle is initiated. This value controls how sensitive " \
259 "the heuristic is to allocation spikes. Decreasing this number " \
260 "increases the sensitivity. ") \
261 \
262 product(double, ShenandoahAdaptiveDecayFactor, 0.1, EXPERIMENTAL, \
263 "The decay factor (alpha) used for values in the weighted " \
264 "moving average of cycle time and allocation rate. " \
265 "Larger values give more weight to recent values.") \
266 range(0,1.0) \
267 \
268 product(bool, ShenandoahAdaptiveIgnoreShortCycles, true, EXPERIMENTAL, \
269 "The adaptive heuristic tracks a moving average of cycle " \
270 "times in order to start a gc before memory is exhausted. " \
271 "In some cases, Shenandoah may skip the evacuation and update " \
272 "reference phases, resulting in a shorter cycle. These may skew " \
273 "the average cycle time downward and may cause the heuristic " \
274 "to wait too long to start a cycle. Disabling this will have " \
275 "the gc run less often, which will reduce CPU utilization, but" \
276 "increase the risk of degenerated cycles.") \
277 \
278 product(uintx, ShenandoahGuaranteedGCInterval, 5*60*1000, EXPERIMENTAL, \
279 "Many heuristics would guarantee a concurrent GC cycle at " \
280 "least with this interval. This is useful when large idle " \
281 "intervals are present, where GC can run without stealing " \
282 "time from active application. Time is in milliseconds. " \
283 "Setting this to 0 disables the feature.") \
284 \
285 product(uintx, ShenandoahGuaranteedOldGCInterval, 10*60*1000, EXPERIMENTAL, \
286 "Run a collection of the old generation at least this often. " \
287 "Heuristics may trigger collections more frequently. Time is in " \
288 "milliseconds. Setting this to 0 disables the feature.") \
289 \
290 product(uintx, ShenandoahGuaranteedYoungGCInterval, 5*60*1000, EXPERIMENTAL, \
291 "Run a collection of the young generation at least this often. " \
292 "Heuristics may trigger collections more frequently. Time is in " \
293 "milliseconds. Setting this to 0 disables the feature.") \
294 \
295 product(bool, ShenandoahAlwaysClearSoftRefs, false, EXPERIMENTAL, \
296 "Unconditionally clear soft references, instead of using any " \
297 "other cleanup policy. This minimizes footprint at expense of" \
298 "more soft reference churn in applications.") \
299 \
300 product(bool, ShenandoahUncommit, true, EXPERIMENTAL, \
301 "Allow to uncommit memory under unused regions and metadata. " \
302 "This optimizes footprint at expense of allocation latency in " \
303 "regions that require committing back. Uncommits would be " \
304 "disabled by some heuristics, or with static heap size.") \
305 \
306 product(uintx, ShenandoahUncommitDelay, 5*60*1000, EXPERIMENTAL, \
307 "Uncommit memory for regions that were not used for more than " \
308 "this time. First use after that would incur allocation stalls. " \
309 "Actively used regions would never be uncommitted, because they " \
310 "do not become unused longer than this delay. Time is in " \
311 "milliseconds. Setting this delay to 0 effectively uncommits " \
312 "regions almost immediately after they become unused.") \
313 \
314 product(bool, ShenandoahRegionSampling, false, EXPERIMENTAL, \
334 product(uintx, ShenandoahControlIntervalAdjustPeriod, 1000, EXPERIMENTAL, \
335 "The time period for one step in control loop interval " \
336 "adjustment. Lower values make adjustments faster, at the " \
337 "expense of higher perf overhead. Time is in milliseconds.") \
338 \
339 product(bool, ShenandoahVerify, false, DIAGNOSTIC, \
340 "Enable internal verification. This would catch many GC bugs, " \
341 "but it would also stall the collector during the verification, " \
342 "which prolongs the pauses and might hide other bugs.") \
343 \
344 product(intx, ShenandoahVerifyLevel, 4, DIAGNOSTIC, \
345 "Verification level, higher levels check more, taking more time. "\
346 "Accepted values are:" \
347 " 0 = basic heap checks; " \
348 " 1 = previous level, plus basic region checks; " \
349 " 2 = previous level, plus all roots; " \
350 " 3 = previous level, plus all reachable objects; " \
351 " 4 = previous level, plus all marked objects") \
352 \
353 product(bool, ShenandoahElasticTLAB, true, DIAGNOSTIC, \
354 "Use Elastic TLABs with Shenandoah. This allows Shenandoah to " \
355 "decrease the size of a TLAB to fit in a region's remaining space") \
356 \
357 product(uintx, ShenandoahEvacReserve, 5, EXPERIMENTAL, \
358 "How much of (young-generation) heap to reserve for " \
359 "(young-generation) evacuations. Larger values allow GC to " \
360 "evacuate more live objects on every cycle, while leaving " \
361 "less headroom for application to allocate while GC is " \
362 "evacuating and updating references. This parameter is " \
363 "consulted at the end of marking, before selecting the " \
364 "collection set. If available memory at this time is smaller " \
365 "than the indicated reserve, the bound on collection set size is "\
366 "adjusted downward. The size of a generational mixed " \
367 "evacuation collection set (comprised of both young and old " \
368 "regions) is also bounded by this parameter. In percents of " \
369 "total (young-generation) heap size.") \
370 range(1,100) \
371 \
372 product(double, ShenandoahEvacWaste, 1.2, EXPERIMENTAL, \
373 "How much waste evacuations produce within the reserved space. " \
374 "Larger values make evacuations more resilient against " \
375 "evacuation conflicts, at expense of evacuating less on each " \
376 "GC cycle. Smaller values increase the risk of evacuation " \
377 "failures, which will trigger stop-the-world Full GC passes.") \
378 range(1.0,100.0) \
379 \
380 product(double, ShenandoahOldEvacWaste, 1.4, EXPERIMENTAL, \
381 "How much waste evacuations produce within the reserved space. " \
382 "Larger values make evacuations more resilient against " \
383 "evacuation conflicts, at expense of evacuating less on each " \
384 "GC cycle. Smaller values increase the risk of evacuation " \
385 "failures, which will trigger stop-the-world Full GC passes.") \
386 range(1.0,100.0) \
387 \
388 product(double, ShenandoahPromoEvacWaste, 1.2, EXPERIMENTAL, \
389 "How much waste promotions produce within the reserved space. " \
390 "Larger values make evacuations more resilient against " \
391 "evacuation conflicts, at expense of promoting less on each " \
392 "GC cycle. Smaller values increase the risk of evacuation " \
393 "failures, which will trigger stop-the-world Full GC passes.") \
394 range(1.0,100.0) \
395 \
396 product(uintx, ShenandoahMaxEvacLABRatio, 0, EXPERIMENTAL, \
397 "Potentially, each running thread maintains a PLAB for " \
398 "evacuating objects into old-gen memory and a GCLAB for " \
399 "evacuating objects into young-gen memory. Each time a thread " \
400 "exhausts its PLAB or GCLAB, a new local buffer is allocated. " \
401 "By default, the new buffer is twice the size of the previous " \
402 "buffer. The sizes are reset to the minimum at the start of " \
403 "each GC pass. This parameter limits the growth of evacuation " \
404 "buffer sizes to its value multiplied by the minimum buffer " \
405 "size. A higher value allows evacuation allocations to be more " \
406 "efficient because less synchronization is required by " \
407 "individual threads. However, a larger value increases the " \
408 "likelihood of evacuation failures, leading to long " \
409 "stop-the-world pauses. This is because a large value " \
410 "allows individual threads to consume large percentages of " \
411 "the total evacuation budget without necessarily effectively " \
412 "filling their local evacuation buffers with evacuated " \
413 "objects. A value of zero means no maximum size is enforced.") \
414 range(0, 1024) \
415 \
416 product(bool, ShenandoahEvacReserveOverflow, true, EXPERIMENTAL, \
417 "Allow evacuations to overflow the reserved space. Enabling it " \
418 "will make evacuations more resilient when evacuation " \
419 "reserve/waste is incorrect, at the risk that application " \
420 "runs out of memory too early.") \
421 \
422 product(uintx, ShenandoahOldEvacRatioPercent, 75, EXPERIMENTAL, \
423 "The maximum proportion of evacuation from old-gen memory, as " \
424 "a percent ratio. The default value 75 denotes that no more " \
425 "than 75% of the collection set evacuation " \
426 "workload may be evacuate to old-gen heap regions. This limits " \
427 "both the promotion of aged regions and the compaction of " \
428 "existing old regions. A value of 75 denotes that the normal " \
429 "young-gen evacuation is increased by up to four fold. " \
430 "A larger value allows quicker promotion and allows" \
431 "a smaller number of mixed evacuations to process " \
432 "the entire list of old-gen collection candidates at the cost " \
433 "of an increased disruption of the normal cadence of young-gen " \
434 "collections. A value of 100 allows a mixed evacuation to " \
435 "focus entirely on old-gen memory, allowing no young-gen " \
436 "regions to be collected, likely resulting in subsequent " \
437 "allocation failures because the allocation pool is not " \
438 "replenished. A value of 0 allows a mixed evacuation to" \
439 "focus entirely on young-gen memory, allowing no old-gen " \
440 "regions to be collected, likely resulting in subsequent " \
441 "promotion failures and triggering of stop-the-world full GC " \
442 "events.") \
443 range(0,100) \
444 \
445 product(uintx, ShenandoahMinYoungPercentage, 20, EXPERIMENTAL, \
446 "The minimum percentage of the heap to use for the young " \
447 "generation. Heuristics will not adjust the young generation " \
448 "to be less than this.") \
449 range(0, 100) \
450 \
451 product(uintx, ShenandoahMaxYoungPercentage, 100, EXPERIMENTAL, \
452 "The maximum percentage of the heap to use for the young " \
453 "generation. Heuristics will not adjust the young generation " \
454 "to be more than this.") \
455 range(0, 100) \
456 \
457 product(bool, ShenandoahPacing, true, EXPERIMENTAL, \
458 "Pace application allocations to give GC chance to start " \
459 "and complete before allocation failure is reached.") \
460 \
461 product(uintx, ShenandoahPacingMaxDelay, 10, EXPERIMENTAL, \
462 "Max delay for pacing application allocations. Larger values " \
463 "provide more resilience against out of memory, at expense at " \
464 "hiding the GC latencies in the allocation path. Time is in " \
465 "milliseconds. Setting it to arbitrarily large value makes " \
466 "GC effectively stall the threads indefinitely instead of going " \
467 "to degenerated or Full GC.") \
468 \
469 product(uintx, ShenandoahPacingIdleSlack, 2, EXPERIMENTAL, \
470 "How much of heap counted as non-taxable allocations during idle "\
471 "phases. Larger value makes the pacing milder when collector is " \
472 "idle, requiring less rendezvous with control thread. Lower " \
473 "value makes the pacing control less responsive to out-of-cycle " \
474 "allocs. In percent of total heap size.") \
475 range(0, 100) \
476 \
511 "that progress is determined by ShenandoahCriticalFreeThreshold") \
512 \
513 product(bool, ShenandoahImplicitGCInvokesConcurrent, false, EXPERIMENTAL, \
514 "Should internally-caused GC requests invoke concurrent cycles, " \
515 "should they do the stop-the-world (Degenerated / Full GC)? " \
516 "Many heuristics automatically enable this. This option is " \
517 "similar to global ExplicitGCInvokesConcurrent.") \
518 \
519 product(bool, ShenandoahHumongousMoves, true, DIAGNOSTIC, \
520 "Allow moving humongous regions. This makes GC more resistant " \
521 "to external fragmentation that may otherwise fail other " \
522 "humongous allocations, at the expense of higher GC copying " \
523 "costs. Currently affects stop-the-world (Full) cycle only.") \
524 \
525 product(bool, ShenandoahOOMDuringEvacALot, false, DIAGNOSTIC, \
526 "Testing: simulate OOM during evacuation.") \
527 \
528 product(bool, ShenandoahAllocFailureALot, false, DIAGNOSTIC, \
529 "Testing: make lots of artificial allocation failures.") \
530 \
531 product(uintx, ShenandoahCoalesceChance, 0, DIAGNOSTIC, \
532 "Testing: Abandon remaining mixed collections with this " \
533 "likelihood. Following each mixed collection, abandon all " \
534 "remaining mixed collection candidate regions with likelihood " \
535 "ShenandoahCoalesceChance. Abandoning a mixed collection will " \
536 "cause the old regions to be made parsable, rather than being " \
537 "evacuated.") \
538 range(0, 100) \
539 \
540 product(intx, ShenandoahMarkScanPrefetch, 32, EXPERIMENTAL, \
541 "How many objects to prefetch ahead when traversing mark bitmaps."\
542 "Set to 0 to disable prefetching.") \
543 range(0, 256) \
544 \
545 product(uintx, ShenandoahMarkLoopStride, 1000, EXPERIMENTAL, \
546 "How many items to process during one marking iteration before " \
547 "checking for cancellation, yielding, etc. Larger values improve "\
548 "marking performance at expense of responsiveness.") \
549 \
550 product(uintx, ShenandoahParallelRegionStride, 1024, EXPERIMENTAL, \
551 "How many regions to process at once during parallel region " \
552 "iteration. Affects heaps with lots of regions.") \
553 \
554 product(size_t, ShenandoahSATBBufferSize, 1 * K, EXPERIMENTAL, \
555 "Number of entries in an SATB log buffer.") \
556 range(1, max_uintx) \
557 \
558 product(uintx, ShenandoahMaxSATBBufferFlushes, 5, EXPERIMENTAL, \
559 "How many times to maximum attempt to flush SATB buffers at the " \
560 "end of concurrent marking.") \
561 \
562 product(bool, ShenandoahSuspendibleWorkers, true, EXPERIMENTAL, \
563 "Suspend concurrent GC worker threads at safepoints") \
564 \
565 product(bool, ShenandoahSATBBarrier, true, DIAGNOSTIC, \
566 "Turn on/off SATB barriers in Shenandoah") \
567 \
568 product(bool, ShenandoahIUBarrier, false, DIAGNOSTIC, \
569 "Turn on/off I-U barriers barriers in Shenandoah") \
570 \
571 product(bool, ShenandoahCardBarrier, false, DIAGNOSTIC, \
572 "Turn on/off card-marking post-write barrier in Shenandoah: " \
573 " true when ShenandoahGCMode is generational, false otherwise") \
574 \
575 product(bool, ShenandoahCASBarrier, true, DIAGNOSTIC, \
576 "Turn on/off CAS barriers in Shenandoah") \
577 \
578 product(bool, ShenandoahCloneBarrier, true, DIAGNOSTIC, \
579 "Turn on/off clone barriers in Shenandoah") \
580 \
581 product(bool, ShenandoahLoadRefBarrier, true, DIAGNOSTIC, \
582 "Turn on/off load-reference barriers in Shenandoah") \
583 \
584 product(bool, ShenandoahStackWatermarkBarrier, true, DIAGNOSTIC, \
585 "Turn on/off stack watermark barriers in Shenandoah") \
586 \
587 develop(bool, ShenandoahVerifyOptoBarriers, false, \
588 "Verify no missing barriers in C2.") \
589 \
590 product(bool, ShenandoahLoopOptsAfterExpansion, true, DIAGNOSTIC, \
591 "Attempt more loop opts after barrier expansion.") \
592 \
593 product(bool, ShenandoahSelfFixing, true, DIAGNOSTIC, \
594 "Fix references with load reference barrier. Disabling this " \
595 "might degrade performance.") \
596 \
597 product(uintx, ShenandoahOldCompactionReserve, 8, EXPERIMENTAL, \
598 "During generational GC, prevent promotions from filling " \
599 "this number of heap regions. These regions are reserved " \
600 "for the purpose of supporting compaction of old-gen " \
601 "memory. Otherwise, old-gen memory cannot be compacted.") \
602 range(0, 128) \
603 \
604 product(bool, ShenandoahAllowOldMarkingPreemption, true, DIAGNOSTIC, \
605 "Allow young generation collections to suspend concurrent" \
606 " marking in the old generation.") \
607 \
608 product(uintx, ShenandoahAgingCyclePeriod, 1, EXPERIMENTAL, \
609 "With generational mode, increment the age of objects and" \
610 "regions each time this many young-gen GC cycles are completed.") \
611 \
612 notproduct(bool, ShenandoahEnableCardStats, false, \
613 "Enable statistics collection related to clean & dirty cards") \
614 \
615 notproduct(int, ShenandoahCardStatsLogInterval, 50, \
616 "Log cumulative card stats every so many remembered set or " \
617 "update refs scans") \
618 // end of GC_SHENANDOAH_FLAGS
619
620 #endif // SHARE_GC_SHENANDOAH_SHENANDOAH_GLOBALS_HPP
|