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
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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, \
185 "Provide heap region sampling data via jvmstat.") \
186 \
187 product(int, ShenandoahRegionSamplingRate, 40, EXPERIMENTAL, \
188 "Sampling rate for heap region sampling. In milliseconds between "\
189 "the samples. Higher values provide more fidelity, at expense " \
190 "of more sampling overhead.") \
191 \
192 product(uintx, ShenandoahControlIntervalMin, 1, EXPERIMENTAL, \
193 "The minimum sleep interval for the control loop that drives " \
194 "the cycles. Lower values would increase GC responsiveness " \
195 "to changing heap conditions, at the expense of higher perf " \
196 "overhead. Time is in milliseconds.") \
197 \
198 product(uintx, ShenandoahControlIntervalMax, 10, EXPERIMENTAL, \
199 "The maximum sleep interval for control loop that drives " \
200 "the cycles. Lower values would increase GC responsiveness " \
201 "to changing heap conditions, at the expense of higher perf " \
202 "overhead. Time is in milliseconds.") \
203 \
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 \
266 product(uintx, ShenandoahPacingCycleSlack, 10, EXPERIMENTAL, \
267 "How much of free space to take as non-taxable allocations " \
268 "the GC cycle. Larger value makes the pacing milder at the " \
269 "beginning of the GC cycle. Lower value makes the pacing less " \
270 "uniform during the cycle. In percent of free space.") \
271 range(0, 100) \
272 \
273 product(double, ShenandoahPacingSurcharge, 1.1, EXPERIMENTAL, \
274 "Additional pacing tax surcharge to help unclutter the heap. " \
275 "Larger values makes the pacing more aggressive. Lower values " \
276 "risk GC cycles finish with less memory than were available at " \
277 "the beginning of it.") \
278 range(1.0, 100.0) \
279 \
280 product(uintx, ShenandoahCriticalFreeThreshold, 1, EXPERIMENTAL, \
281 "How much of the heap needs to be free after recovery cycles, " \
282 "either Degenerated or Full GC to be claimed successful. If this "\
283 "much space is not available, next recovery step would be " \
284 "triggered.") \
285 range(0, 100) \
286 \
287 product(bool, ShenandoahDegeneratedGC, true, DIAGNOSTIC, \
288 "Enable Degenerated GC as the graceful degradation step. " \
289 "Disabling this option leads to degradation to Full GC instead. " \
290 "When running in passive mode, this can be toggled to measure " \
291 "either Degenerated GC or Full GC costs.") \
292 \
293 product(uintx, ShenandoahFullGCThreshold, 3, EXPERIMENTAL, \
294 "How many back-to-back Degenerated GCs should happen before " \
295 "going to a Full GC.") \
296 \
297 product(bool, ShenandoahImplicitGCInvokesConcurrent, false, EXPERIMENTAL, \
298 "Should internally-caused GC requests invoke concurrent cycles, " \
299 "should they do the stop-the-world (Degenerated / Full GC)? " \
300 "Many heuristics automatically enable this. This option is " \
301 "similar to global ExplicitGCInvokesConcurrent.") \
302 \
303 product(bool, ShenandoahHumongousMoves, true, DIAGNOSTIC, \
304 "Allow moving humongous regions. This makes GC more resistant " \
305 "to external fragmentation that may otherwise fail other " \
306 "humongous allocations, at the expense of higher GC copying " \
307 "costs. Currently affects stop-the-world (Full) cycle only.") \
308 \
309 product(bool, ShenandoahOOMDuringEvacALot, false, DIAGNOSTIC, \
310 "Testing: simulate OOM during evacuation.") \
311 \
312 product(bool, ShenandoahAllocFailureALot, false, DIAGNOSTIC, \
313 "Testing: make lots of artificial allocation failures.") \
314 \
315 product(intx, ShenandoahMarkScanPrefetch, 32, EXPERIMENTAL, \
316 "How many objects to prefetch ahead when traversing mark bitmaps."\
317 "Set to 0 to disable prefetching.") \
318 range(0, 256) \
319 \
320 product(uintx, ShenandoahMarkLoopStride, 1000, EXPERIMENTAL, \
321 "How many items to process during one marking iteration before " \
322 "checking for cancellation, yielding, etc. Larger values improve "\
323 "marking performance at expense of responsiveness.") \
324 \
325 product(uintx, ShenandoahParallelRegionStride, 1024, EXPERIMENTAL, \
326 "How many regions to process at once during parallel region " \
327 "iteration. Affects heaps with lots of regions.") \
328 \
329 product(size_t, ShenandoahSATBBufferSize, 1 * K, EXPERIMENTAL, \
330 "Number of entries in an SATB log buffer.") \
331 range(1, max_uintx) \
332 \
333 product(uintx, ShenandoahMaxSATBBufferFlushes, 5, EXPERIMENTAL, \
334 "How many times to maximum attempt to flush SATB buffers at the " \
335 "end of concurrent marking.") \
336 \
337 product(bool, ShenandoahSuspendibleWorkers, false, EXPERIMENTAL, \
338 "Suspend concurrent GC worker threads at safepoints") \
339 \
340 product(bool, ShenandoahSATBBarrier, true, DIAGNOSTIC, \
341 "Turn on/off SATB barriers in Shenandoah") \
342 \
343 product(bool, ShenandoahIUBarrier, false, DIAGNOSTIC, \
344 "Turn on/off I-U barriers barriers in Shenandoah") \
345 \
346 product(bool, ShenandoahCASBarrier, true, DIAGNOSTIC, \
347 "Turn on/off CAS barriers in Shenandoah") \
348 \
349 product(bool, ShenandoahCloneBarrier, true, DIAGNOSTIC, \
350 "Turn on/off clone barriers in Shenandoah") \
351 \
352 product(bool, ShenandoahLoadRefBarrier, true, DIAGNOSTIC, \
353 "Turn on/off load-reference barriers in Shenandoah") \
354 \
355 product(bool, ShenandoahNMethodBarrier, true, DIAGNOSTIC, \
356 "Turn on/off NMethod entry barriers in Shenandoah") \
357 \
358 product(bool, ShenandoahStackWatermarkBarrier, true, DIAGNOSTIC, \
359 "Turn on/off stack watermark barriers in Shenandoah") \
360 \
361 develop(bool, ShenandoahVerifyOptoBarriers, false, \
362 "Verify no missing barriers in C2.") \
363 \
364 product(bool, ShenandoahLoopOptsAfterExpansion, true, DIAGNOSTIC, \
365 "Attempt more loop opts after barrier expansion.") \
366 \
367 product(bool, ShenandoahSelfFixing, true, DIAGNOSTIC, \
368 "Fix references with load reference barrier. Disabling this " \
369 "might degrade performance.")
370
371 // end of GC_SHENANDOAH_FLAGS
372
373 #endif // SHARE_GC_SHENANDOAH_SHENANDOAH_GLOBALS_HPP