1 /*
2 * Copyright (c) 2020, 2024, 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 *
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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 range, \
34 constraint) \
35 \
36 product(size_t, ShenandoahRegionSize, 0, EXPERIMENTAL, \
37 "Static heap region size. Set zero to enable automatic sizing.") \
38 \
39 product(size_t, ShenandoahTargetNumRegions, 2048, EXPERIMENTAL, \
40 "With automatic region sizing, this is the approximate number " \
41 "of regions that would be used, within min/max region size " \
42 "limits.") \
43 \
44 product(size_t, ShenandoahMinRegionSize, 256 * K, EXPERIMENTAL, \
45 "With automatic region sizing, the regions would be at least " \
46 "this large.") \
47 \
48 product(size_t, ShenandoahMaxRegionSize, 32 * M, EXPERIMENTAL, \
49 "With automatic region sizing, the regions would be at most " \
50 "this large.") \
51 \
52 product(intx, ShenandoahHumongousThreshold, 100, EXPERIMENTAL, \
53 "Humongous objects are allocated in separate regions. " \
54 "This setting defines how large the object should be to be " \
55 "deemed humongous. Value is in percents of heap region size. " \
56 "This also caps the maximum TLAB size.") \
57 range(1, 100) \
58 \
59 product(ccstr, ShenandoahGCMode, "satb", \
60 "GC mode to use. Among other things, this defines which " \
61 "barriers are in in use. Possible values are:" \
62 " satb - snapshot-at-the-beginning concurrent GC (three pass mark-evac-update);" \
63 " iu - incremental-update concurrent GC (three pass mark-evac-update);" \
64 " passive - stop the world GC only (either degenerated or full)") \
65 \
66 product(ccstr, ShenandoahGCHeuristics, "adaptive", \
67 "GC heuristics to use. This fine-tunes the GC mode selected, " \
68 "by choosing when to start the GC, how much to process on each " \
69 "cycle, and what other features to automatically enable. " \
70 "Possible values are:" \
71 " adaptive - adapt to maintain the given amount of free heap " \
72 "at all times, even during the GC cycle;" \
73 " static - trigger GC when free heap falls below the threshold;" \
74 " aggressive - run GC continuously, try to evacuate everything;" \
75 " compact - run GC more frequently and with deeper targets to " \
76 "free up more memory.") \
77 \
78 product(uintx, ShenandoahGarbageThreshold, 25, EXPERIMENTAL, \
79 "How much garbage a region has to contain before it would be " \
80 "taken for collection. This a guideline only, as GC heuristics " \
81 "may select the region for collection even if it has little " \
82 "garbage. This also affects how much internal fragmentation the " \
83 "collector accepts. In percents of heap region size.") \
84 range(0,100) \
85 \
86 product(uintx, ShenandoahInitFreeThreshold, 70, EXPERIMENTAL, \
87 "How much heap should be free before some heuristics trigger the "\
88 "initial (learning) cycles. Affects cycle frequency on startup " \
89 "and after drastic state changes, e.g. after degenerated/full " \
90 "GC cycles. In percents of (soft) max heap size.") \
91 range(0,100) \
92 \
93 product(uintx, ShenandoahMinFreeThreshold, 10, EXPERIMENTAL, \
94 "How much heap should be free before most heuristics trigger the "\
95 "collection, even without other triggers. Provides the safety " \
96 "margin for many heuristics. In percents of (soft) max heap size.")\
97 range(0,100) \
98 \
99 product(uintx, ShenandoahAllocationThreshold, 0, EXPERIMENTAL, \
100 "How many new allocations should happen since the last GC cycle " \
101 "before some heuristics trigger the collection. In percents of " \
102 "(soft) max heap size. Set to zero to effectively disable.") \
103 range(0,100) \
104 \
105 product(uintx, ShenandoahAllocSpikeFactor, 5, EXPERIMENTAL, \
106 "How much of heap should some heuristics reserve for absorbing " \
107 "the allocation spikes. Larger value wastes more memory in " \
108 "non-emergency cases, but provides more safety in emergency " \
109 "cases. In percents of (soft) max heap size.") \
110 range(0,100) \
111 \
112 product(uintx, ShenandoahLearningSteps, 5, EXPERIMENTAL, \
113 "The number of cycles some heuristics take to collect in order " \
114 "to learn application and GC performance.") \
115 range(0,100) \
116 \
117 product(uintx, ShenandoahImmediateThreshold, 90, EXPERIMENTAL, \
118 "The cycle may shortcut when enough garbage can be reclaimed " \
119 "from the immediate garbage (completely garbage regions). " \
120 "In percents of total garbage found. Setting this threshold " \
121 "to 100 effectively disables the shortcut.") \
122 range(0,100) \
123 \
124 product(uintx, ShenandoahAdaptiveSampleFrequencyHz, 10, EXPERIMENTAL, \
125 "The number of times per second to update the allocation rate " \
126 "moving average.") \
127 \
128 product(uintx, ShenandoahAdaptiveSampleSizeSeconds, 10, EXPERIMENTAL, \
129 "The size of the moving window over which the average " \
130 "allocation rate is maintained. The total number of samples " \
131 "is the product of this number and the sample frequency.") \
132 \
133 product(double, ShenandoahAdaptiveInitialConfidence, 1.8, EXPERIMENTAL, \
134 "The number of standard deviations used to determine an initial " \
135 "margin of error for the average cycle time and average " \
136 "allocation rate. Increasing this value will cause the " \
137 "heuristic to initiate more concurrent cycles." ) \
138 \
139 product(double, ShenandoahAdaptiveInitialSpikeThreshold, 1.8, EXPERIMENTAL, \
140 "If the most recently sampled allocation rate is more than " \
141 "this many standard deviations away from the moving average, " \
142 "then a cycle is initiated. This value controls how sensitive " \
143 "the heuristic is to allocation spikes. Decreasing this number " \
144 "increases the sensitivity. ") \
145 \
146 product(double, ShenandoahAdaptiveDecayFactor, 0.5, EXPERIMENTAL, \
147 "The decay factor (alpha) used for values in the weighted " \
148 "moving average of cycle time and allocation rate. " \
149 "Larger values give more weight to recent values.") \
150 range(0,1.0) \
151 \
152 product(uintx, ShenandoahGuaranteedGCInterval, 5*60*1000, EXPERIMENTAL, \
153 "Many heuristics would guarantee a concurrent GC cycle at " \
154 "least with this interval. This is useful when large idle " \
155 "intervals are present, where GC can run without stealing " \
156 "time from active application. Time is in milliseconds. " \
157 "Setting this to 0 disables the feature.") \
158 \
159 product(bool, ShenandoahAlwaysClearSoftRefs, false, EXPERIMENTAL, \
160 "Unconditionally clear soft references, instead of using any " \
161 "other cleanup policy. This minimizes footprint at expense of" \
162 "more soft reference churn in applications.") \
163 \
164 product(bool, ShenandoahUncommit, true, EXPERIMENTAL, \
165 "Allow to uncommit memory under unused regions and metadata. " \
166 "This optimizes footprint at expense of allocation latency in " \
167 "regions that require committing back. Uncommits would be " \
168 "disabled by some heuristics, or with static heap size.") \
169 \
170 product(uintx, ShenandoahUncommitDelay, 5*60*1000, EXPERIMENTAL, \
171 "Uncommit memory for regions that were not used for more than " \
172 "this time. First use after that would incur allocation stalls. " \
173 "Actively used regions would never be uncommitted, because they " \
174 "do not become unused longer than this delay. Time is in " \
175 "milliseconds. Setting this delay to 0 effectively uncommits " \
176 "regions almost immediately after they become unused.") \
177 \
178 product(bool, ShenandoahRegionSampling, false, EXPERIMENTAL, \
179 "Provide heap region sampling data via jvmstat.") \
180 \
181 product(int, ShenandoahRegionSamplingRate, 40, EXPERIMENTAL, \
182 "Sampling rate for heap region sampling. In milliseconds between "\
183 "the samples. Higher values provide more fidelity, at expense " \
184 "of more sampling overhead.") \
185 \
186 product(uintx, ShenandoahControlIntervalMin, 1, EXPERIMENTAL, \
187 "The minimum sleep interval for the control loop that drives " \
188 "the cycles. Lower values would increase GC responsiveness " \
189 "to changing heap conditions, at the expense of higher perf " \
190 "overhead. Time is in milliseconds.") \
191 \
192 product(uintx, ShenandoahControlIntervalMax, 10, EXPERIMENTAL, \
193 "The maximum sleep interval for 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, ShenandoahControlIntervalAdjustPeriod, 1000, EXPERIMENTAL, \
199 "The time period for one step in control loop interval " \
200 "adjustment. Lower values make adjustments faster, at the " \
201 "expense of higher perf overhead. Time is in milliseconds.") \
202 \
203 product(bool, ShenandoahVerify, false, DIAGNOSTIC, \
204 "Enable internal verification. This would catch many GC bugs, " \
205 "but it would also stall the collector during the verification, " \
206 "which prolongs the pauses and might hide other bugs.") \
207 \
208 product(intx, ShenandoahVerifyLevel, 4, DIAGNOSTIC, \
209 "Verification level, higher levels check more, taking more time. "\
210 "Accepted values are:" \
211 " 0 = basic heap checks; " \
212 " 1 = previous level, plus basic region checks; " \
213 " 2 = previous level, plus all roots; " \
214 " 3 = previous level, plus all reachable objects; " \
215 " 4 = previous level, plus all marked objects") \
216 \
217 product(uintx, ShenandoahEvacReserve, 5, EXPERIMENTAL, \
218 "How much of heap to reserve for evacuations. Larger values make "\
219 "GC evacuate more live objects on every cycle, while leaving " \
220 "less headroom for application to allocate in. In percents of " \
221 "total heap size.") \
222 range(1,100) \
223 \
224 product(double, ShenandoahEvacWaste, 1.2, EXPERIMENTAL, \
225 "How much waste evacuations produce within the reserved space. " \
226 "Larger values make evacuations more resilient against " \
227 "evacuation conflicts, at expense of evacuating less on each " \
228 "GC cycle.") \
229 range(1.0,100.0) \
230 \
231 product(bool, ShenandoahEvacReserveOverflow, true, EXPERIMENTAL, \
232 "Allow evacuations to overflow the reserved space. Enabling it " \
233 "will make evacuations more resilient when evacuation " \
234 "reserve/waste is incorrect, at the risk that application " \
235 "runs out of memory too early.") \
236 \
237 product(bool, ShenandoahPacing, true, EXPERIMENTAL, \
238 "Pace application allocations to give GC chance to start " \
239 "and complete before allocation failure is reached.") \
240 \
241 product(uintx, ShenandoahPacingMaxDelay, 10, EXPERIMENTAL, \
242 "Max delay for pacing application allocations. Larger values " \
243 "provide more resilience against out of memory, at expense at " \
244 "hiding the GC latencies in the allocation path. Time is in " \
245 "milliseconds. Setting it to arbitrarily large value makes " \
246 "GC effectively stall the threads indefinitely instead of going " \
247 "to degenerated or Full GC.") \
248 \
249 product(uintx, ShenandoahPacingIdleSlack, 2, EXPERIMENTAL, \
250 "How much of heap counted as non-taxable allocations during idle "\
251 "phases. Larger value makes the pacing milder when collector is " \
252 "idle, requiring less rendezvous with control thread. Lower " \
253 "value makes the pacing control less responsive to out-of-cycle " \
254 "allocs. In percent of total heap size.") \
255 range(0, 100) \
256 \
257 product(uintx, ShenandoahPacingCycleSlack, 10, EXPERIMENTAL, \
258 "How much of free space to take as non-taxable allocations " \
259 "the GC cycle. Larger value makes the pacing milder at the " \
260 "beginning of the GC cycle. Lower value makes the pacing less " \
261 "uniform during the cycle. In percent of free space.") \
262 range(0, 100) \
263 \
264 product(double, ShenandoahPacingSurcharge, 1.1, EXPERIMENTAL, \
265 "Additional pacing tax surcharge to help unclutter the heap. " \
266 "Larger values makes the pacing more aggressive. Lower values " \
267 "risk GC cycles finish with less memory than were available at " \
268 "the beginning of it.") \
269 range(1.0, 100.0) \
270 \
271 product(uintx, ShenandoahCriticalFreeThreshold, 1, EXPERIMENTAL, \
272 "How much of the heap needs to be free after recovery cycles, " \
273 "either Degenerated or Full GC to be claimed successful. If this "\
274 "much space is not available, next recovery step would be " \
275 "triggered.") \
276 range(0, 100) \
277 \
278 product(bool, ShenandoahDegeneratedGC, true, DIAGNOSTIC, \
279 "Enable Degenerated GC as the graceful degradation step. " \
280 "Disabling this option leads to degradation to Full GC instead. " \
281 "When running in passive mode, this can be toggled to measure " \
282 "either Degenerated GC or Full GC costs.") \
283 \
284 product(uintx, ShenandoahFullGCThreshold, 3, EXPERIMENTAL, \
285 "How many back-to-back Degenerated GCs should happen before " \
286 "going to a Full GC.") \
287 \
288 product(uintx, ShenandoahNoProgressThreshold, 5, EXPERIMENTAL, \
289 "After this number of consecutive Full GCs fail to make " \
290 "progress, Shenandoah will raise out of memory errors. Note " \
291 "that progress is determined by ShenandoahCriticalFreeThreshold") \
292 \
293 product(bool, ShenandoahImplicitGCInvokesConcurrent, false, EXPERIMENTAL, \
294 "Should internally-caused GC requests invoke concurrent cycles, " \
295 "should they do the stop-the-world (Degenerated / Full GC)? " \
296 "Many heuristics automatically enable this. This option is " \
297 "similar to global ExplicitGCInvokesConcurrent.") \
298 \
299 product(bool, ShenandoahHumongousMoves, true, DIAGNOSTIC, \
300 "Allow moving humongous regions. This makes GC more resistant " \
301 "to external fragmentation that may otherwise fail other " \
302 "humongous allocations, at the expense of higher GC copying " \
303 "costs. Currently affects stop-the-world (Full) cycle only.") \
304 \
305 product(bool, ShenandoahOOMDuringEvacALot, false, DIAGNOSTIC, \
306 "Testing: simulate OOM during evacuation.") \
307 \
308 product(bool, ShenandoahAllocFailureALot, false, DIAGNOSTIC, \
309 "Testing: make lots of artificial allocation failures.") \
310 \
311 product(intx, ShenandoahMarkScanPrefetch, 32, EXPERIMENTAL, \
312 "How many objects to prefetch ahead when traversing mark bitmaps."\
313 "Set to 0 to disable prefetching.") \
314 range(0, 256) \
315 \
316 product(uintx, ShenandoahMarkLoopStride, 1000, EXPERIMENTAL, \
317 "How many items to process during one marking iteration before " \
318 "checking for cancellation, yielding, etc. Larger values improve "\
319 "marking performance at expense of responsiveness.") \
320 \
321 product(uintx, ShenandoahParallelRegionStride, 1024, EXPERIMENTAL, \
322 "How many regions to process at once during parallel region " \
323 "iteration. Affects heaps with lots of regions.") \
324 \
325 product(size_t, ShenandoahSATBBufferSize, 1 * K, EXPERIMENTAL, \
326 "Number of entries in an SATB log buffer.") \
327 range(1, max_uintx) \
328 \
329 product(uintx, ShenandoahMaxSATBBufferFlushes, 5, EXPERIMENTAL, \
330 "How many times to maximum attempt to flush SATB buffers at the " \
331 "end of concurrent marking.") \
332 \
333 product(bool, ShenandoahSATBBarrier, true, DIAGNOSTIC, \
334 "Turn on/off SATB barriers in Shenandoah") \
335 \
336 product(bool, ShenandoahIUBarrier, false, DIAGNOSTIC, \
337 "Turn on/off I-U barriers barriers in Shenandoah") \
338 \
339 product(bool, ShenandoahCASBarrier, true, DIAGNOSTIC, \
340 "Turn on/off CAS barriers in Shenandoah") \
341 \
342 product(bool, ShenandoahCloneBarrier, true, DIAGNOSTIC, \
343 "Turn on/off clone barriers in Shenandoah") \
344 \
345 product(bool, ShenandoahLoadRefBarrier, true, DIAGNOSTIC, \
346 "Turn on/off load-reference barriers in Shenandoah") \
347 \
348 product(bool, ShenandoahStackWatermarkBarrier, true, DIAGNOSTIC, \
349 "Turn on/off stack watermark barriers in Shenandoah") \
350 \
351 develop(bool, ShenandoahVerifyOptoBarriers, trueInDebug, \
352 "Verify no missing barriers in C2.") \
353 \
354
355 // end of GC_SHENANDOAH_FLAGS
356
357 #endif // SHARE_GC_SHENANDOAH_SHENANDOAH_GLOBALS_HPP