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 *
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 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, \
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 \
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
|
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 * 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 range, \
35 constraint) \
36 \
37 product(uintx, ShenandoahGenerationalHumongousReserve, 0, EXPERIMENTAL, \
38 "(Generational mode only) What percent of the heap should be " \
39 "reserved for humongous objects if possible. Old-generation " \
40 "collections will endeavor to evacuate old-gen regions within " \
41 "this reserved area even if these regions do not contain high " \
42 "percentage of garbage. Setting a larger value will cause " \
43 "more frequent old-gen collections. A smaller value will " \
44 "increase the likelihood that humongous object allocations " \
45 "fail, resulting in stop-the-world full GCs.") \
46 range(0,100) \
47 \
48 product(double, ShenandoahMinOldGenGrowthPercent, 12.5, EXPERIMENTAL, \
49 "(Generational mode only) If the usage within old generation " \
50 "has grown by at least this percent of its live memory size " \
51 "at completion of the most recent old-generation marking " \
52 "effort, heuristics may trigger the start of a new old-gen " \
53 "collection.") \
54 range(0.0,100.0) \
55 \
56 product(uintx, ShenandoahIgnoreOldGrowthBelowPercentage,10, EXPERIMENTAL, \
57 "(Generational mode only) If the total usage of the old " \
58 "generation is smaller than this percent, we do not trigger " \
59 "old gen collections even if old has grown, except when " \
60 "ShenandoahGenerationalDoNotIgnoreGrowthAfterYoungCycles " \
61 "consecutive cycles have been completed following the " \
62 "preceding old-gen collection.") \
63 range(0,100) \
64 \
65 product(uintx, ShenandoahDoNotIgnoreGrowthAfterYoungCycles, \
66 50, EXPERIMENTAL, \
67 "(Generational mode only) Even if the usage of old generation " \
68 "is below ShenandoahIgnoreOldGrowthBelowPercentage, " \
69 "trigger an old-generation mark if old has grown and this " \
70 "many consecutive young-gen collections have been " \
71 "completed following the preceding old-gen collection.") \
72 \
73 product(bool, ShenandoahGenerationalCensusAtEvac, false, EXPERIMENTAL, \
74 "(Generational mode only) Object age census at evacuation, " \
75 "rather than during marking.") \
76 \
77 product(bool, ShenandoahGenerationalAdaptiveTenuring, true, EXPERIMENTAL, \
78 "(Generational mode only) Dynamically adapt tenuring age.") \
79 \
80 product(bool, ShenandoahGenerationalCensusIgnoreOlderCohorts, true, \
81 EXPERIMENTAL,\
82 "(Generational mode only) Ignore mortality rates older than the " \
83 "oldest cohort under the tenuring age for the last cycle." ) \
84 \
85 product(uintx, ShenandoahGenerationalMinTenuringAge, 1, EXPERIMENTAL, \
86 "(Generational mode only) Floor for adaptive tenuring age. " \
87 "Setting floor and ceiling to the same value fixes the tenuring " \
88 "age; setting both to 1 simulates a poor approximation to " \
89 "AlwaysTenure, and setting both to 16 simulates NeverTenure.") \
90 range(1,16) \
91 \
92 product(uintx, ShenandoahGenerationalMaxTenuringAge, 15, EXPERIMENTAL, \
93 "(Generational mode only) Ceiling for adaptive tenuring age. " \
94 "Setting floor and ceiling to the same value fixes the tenuring " \
95 "age; setting both to 1 simulates a poor approximation to " \
96 "AlwaysTenure, and setting both to 16 simulates NeverTenure.") \
97 range(1,16) \
98 \
99 product(double, ShenandoahGenerationalTenuringMortalityRateThreshold, \
100 0.1, EXPERIMENTAL, \
101 "(Generational mode only) Cohort mortality rates below this " \
102 "value will be treated as indicative of longevity, leading to " \
103 "tenuring. A lower value delays tenuring, a higher value hastens "\
104 "it. Used only when ShenandoahGenerationalhenAdaptiveTenuring is "\
105 "enabled.") \
106 range(0.001,0.999) \
107 \
108 product(size_t, ShenandoahGenerationalTenuringCohortPopulationThreshold, \
109 4*K, EXPERIMENTAL, \
110 "(Generational mode only) Cohorts whose population is lower than "\
111 "this value in the previous census are ignored wrt tenuring " \
112 "decisions. Effectively this makes then tenurable as soon as all "\
113 "older cohorts are. Set this value to the largest cohort " \
114 "population volume that you are comfortable ignoring when making "\
115 "tenuring decisions.") \
116 \
117 product(size_t, ShenandoahRegionSize, 0, EXPERIMENTAL, \
118 "Static heap region size. Set zero to enable automatic sizing.") \
119 \
120 product(size_t, ShenandoahTargetNumRegions, 2048, EXPERIMENTAL, \
121 "With automatic region sizing, this is the approximate number " \
122 "of regions that would be used, within min/max region size " \
123 "limits.") \
124 \
125 product(size_t, ShenandoahMinRegionSize, 256 * K, EXPERIMENTAL, \
126 "With automatic region sizing, the regions would be at least " \
127 "this large.") \
128 \
129 product(size_t, ShenandoahMaxRegionSize, 32 * M, EXPERIMENTAL, \
130 "With automatic region sizing, the regions would be at most " \
131 "this large.") \
132 \
133 product(intx, ShenandoahHumongousThreshold, 100, EXPERIMENTAL, \
134 "Humongous objects are allocated in separate regions. " \
135 "This setting defines how large the object should be to be " \
136 "deemed humongous. Value is in percents of heap region size. " \
137 "This also caps the maximum TLAB size.") \
138 range(1, 100) \
139 \
140 product(ccstr, ShenandoahGCMode, "satb", \
141 "GC mode to use. Among other things, this defines which " \
142 "barriers are in in use. Possible values are:" \
143 " satb - snapshot-at-the-beginning concurrent GC (three pass mark-evac-update);" \
144 " iu - incremental-update concurrent GC (three pass mark-evac-update);" \
145 " passive - stop the world GC only (either degenerated or full);" \
146 " generational - generational concurrent GC") \
147 \
148 product(ccstr, ShenandoahGCHeuristics, "adaptive", \
149 "GC heuristics to use. This fine-tunes the GC mode selected, " \
150 "by choosing when to start the GC, how much to process on each " \
151 "cycle, and what other features to automatically enable. " \
152 "Possible values are:" \
153 " adaptive - adapt to maintain the given amount of free heap " \
154 "at all times, even during the GC cycle;" \
155 " static - trigger GC when free heap falls below the threshold;" \
156 " aggressive - run GC continuously, try to evacuate everything;" \
157 " compact - run GC more frequently and with deeper targets to " \
158 "free up more memory.") \
159 \
160 product(uintx, ShenandoahExpeditePromotionsThreshold, 5, EXPERIMENTAL, \
161 "When Shenandoah expects to promote at least this percentage " \
162 "of the young generation, trigger a young collection to " \
163 "expedite these promotions.") \
164 range(0,100) \
165 \
166 product(uintx, ShenandoahExpediteMixedThreshold, 10, EXPERIMENTAL, \
167 "When there are this many old regions waiting to be collected, " \
168 "trigger a mixed collection immediately.") \
169 \
170 product(uintx, ShenandoahGarbageThreshold, 25, EXPERIMENTAL, \
171 "How much garbage a region has to contain before it would be " \
172 "taken for collection. This a guideline only, as GC heuristics " \
173 "may select the region for collection even if it has little " \
174 "garbage. This also affects how much internal fragmentation the " \
175 "collector accepts. In percents of heap region size.") \
176 range(0,100) \
177 \
178 product(uintx, ShenandoahOldGarbageThreshold, 15, EXPERIMENTAL, \
179 "How much garbage an old region has to contain before it would " \
180 "be taken for collection.") \
181 range(0,100) \
182 \
183 product(uintx, ShenandoahIgnoreGarbageThreshold, 5, EXPERIMENTAL, \
184 "When less than this amount of garbage (as a percentage of " \
185 "region size) exists within a region, the region will not be " \
186 "added to the collection set, even when the heuristic has " \
187 "chosen to aggressively add regions with less than " \
188 "ShenandoahGarbageThreshold amount of garbage into the " \
189 "collection set.") \
190 range(0,100) \
191 \
192 product(uintx, ShenandoahInitFreeThreshold, 70, EXPERIMENTAL, \
193 "When less than this amount of memory is free within the" \
194 "heap or generation, trigger a learning cycle if we are " \
195 "in learning mode. Learning mode happens during initialization " \
196 "and following a drastic state change, such as following a " \
197 "degenerated or Full GC cycle. In percents of soft max " \
198 "heap size.") \
199 range(0,100) \
200 \
201 product(uintx, ShenandoahMinFreeThreshold, 10, EXPERIMENTAL, \
202 "Percentage of free heap memory (or young generation, in " \
203 "generational mode) below which most heuristics trigger " \
204 "collection independent of other triggers. Provides a safety " \
205 "margin for many heuristics. In percents of (soft) max heap " \
206 "size.") \
207 range(0,100) \
208 \
209 product(uintx, ShenandoahAllocationThreshold, 0, EXPERIMENTAL, \
210 "How many new allocations should happen since the last GC cycle " \
211 "before some heuristics trigger the collection. In percents of " \
212 "(soft) max heap size. Set to zero to effectively disable.") \
213 range(0,100) \
214 \
215 product(uintx, ShenandoahAllocSpikeFactor, 5, EXPERIMENTAL, \
216 "How much of heap should some heuristics reserve for absorbing " \
217 "the allocation spikes. Larger value wastes more memory in " \
218 "non-emergency cases, but provides more safety in emergency " \
219 "cases. In percents of (soft) max heap size.") \
220 range(0,100) \
221 \
222 product(uintx, ShenandoahLearningSteps, 10, EXPERIMENTAL, \
223 "The number of cycles some heuristics take to collect in order " \
224 "to learn application and GC performance.") \
225 range(0,100) \
226 \
227 product(uintx, ShenandoahImmediateThreshold, 70, EXPERIMENTAL, \
228 "The cycle may shortcut when enough garbage can be reclaimed " \
229 "from the immediate garbage (completely garbage regions). " \
230 "In percents of total garbage found. Setting this threshold " \
231 "to 100 effectively disables the shortcut.") \
232 range(0,100) \
233 \
234 product(uintx, ShenandoahAdaptiveSampleFrequencyHz, 10, EXPERIMENTAL, \
235 "The number of times per second to update the allocation rate " \
236 "moving average.") \
237 \
238 product(uintx, ShenandoahAdaptiveSampleSizeSeconds, 10, EXPERIMENTAL, \
239 "The size of the moving window over which the average " \
240 "allocation rate is maintained. The total number of samples " \
241 "is the product of this number and the sample frequency.") \
242 \
243 product(double, ShenandoahAdaptiveInitialConfidence, 1.8, EXPERIMENTAL, \
244 "The number of standard deviations used to determine an initial " \
245 "margin of error for the average cycle time and average " \
246 "allocation rate. Increasing this value will cause the " \
247 "heuristic to initiate more concurrent cycles." ) \
248 \
249 product(double, ShenandoahAdaptiveInitialSpikeThreshold, 1.8, EXPERIMENTAL, \
250 "If the most recently sampled allocation rate is more than " \
251 "this many standard deviations away from the moving average, " \
252 "then a cycle is initiated. This value controls how sensitive " \
253 "the heuristic is to allocation spikes. Decreasing this number " \
254 "increases the sensitivity. ") \
255 \
256 product(double, ShenandoahAdaptiveDecayFactor, 0.1, EXPERIMENTAL, \
257 "The decay factor (alpha) used for values in the weighted " \
258 "moving average of cycle time and allocation rate. " \
259 "Larger values give more weight to recent values.") \
260 range(0,1.0) \
261 \
262 product(bool, ShenandoahAdaptiveIgnoreShortCycles, true, EXPERIMENTAL, \
263 "The adaptive heuristic tracks a moving average of cycle " \
264 "times in order to start a gc before memory is exhausted. " \
265 "In some cases, Shenandoah may skip the evacuation and update " \
266 "reference phases, resulting in a shorter cycle. These may skew " \
267 "the average cycle time downward and may cause the heuristic " \
268 "to wait too long to start a cycle. Disabling this will have " \
269 "the gc run less often, which will reduce CPU utilization, but" \
270 "increase the risk of degenerated cycles.") \
271 \
272 product(uintx, ShenandoahGuaranteedGCInterval, 5*60*1000, EXPERIMENTAL, \
273 "Many heuristics would guarantee a concurrent GC cycle at " \
274 "least with this interval. This is useful when large idle " \
275 "intervals are present, where GC can run without stealing " \
276 "time from active application. Time is in milliseconds. " \
277 "Setting this to 0 disables the feature.") \
278 \
279 product(uintx, ShenandoahGuaranteedOldGCInterval, 10*60*1000, EXPERIMENTAL, \
280 "Run a collection of the old generation at least this often. " \
281 "Heuristics may trigger collections more frequently. Time is in " \
282 "milliseconds. Setting this to 0 disables the feature.") \
283 \
284 product(uintx, ShenandoahGuaranteedYoungGCInterval, 5*60*1000, EXPERIMENTAL, \
285 "Run a collection of the young generation at least this often. " \
286 "Heuristics may trigger collections more frequently. Time is in " \
287 "milliseconds. Setting this to 0 disables the feature.") \
288 \
289 product(bool, ShenandoahAlwaysClearSoftRefs, false, EXPERIMENTAL, \
290 "Unconditionally clear soft references, instead of using any " \
291 "other cleanup policy. This minimizes footprint at expense of" \
292 "more soft reference churn in applications.") \
293 \
294 product(bool, ShenandoahUncommit, true, EXPERIMENTAL, \
295 "Allow to uncommit memory under unused regions and metadata. " \
296 "This optimizes footprint at expense of allocation latency in " \
297 "regions that require committing back. Uncommits would be " \
298 "disabled by some heuristics, or with static heap size.") \
299 \
300 product(uintx, ShenandoahUncommitDelay, 5*60*1000, EXPERIMENTAL, \
301 "Uncommit memory for regions that were not used for more than " \
302 "this time. First use after that would incur allocation stalls. " \
303 "Actively used regions would never be uncommitted, because they " \
304 "do not become unused longer than this delay. Time is in " \
305 "milliseconds. Setting this delay to 0 effectively uncommits " \
306 "regions almost immediately after they become unused.") \
307 \
308 product(bool, ShenandoahRegionSampling, false, EXPERIMENTAL, \
328 product(uintx, ShenandoahControlIntervalAdjustPeriod, 1000, EXPERIMENTAL, \
329 "The time period for one step in control loop interval " \
330 "adjustment. Lower values make adjustments faster, at the " \
331 "expense of higher perf overhead. Time is in milliseconds.") \
332 \
333 product(bool, ShenandoahVerify, false, DIAGNOSTIC, \
334 "Enable internal verification. This would catch many GC bugs, " \
335 "but it would also stall the collector during the verification, " \
336 "which prolongs the pauses and might hide other bugs.") \
337 \
338 product(intx, ShenandoahVerifyLevel, 4, DIAGNOSTIC, \
339 "Verification level, higher levels check more, taking more time. "\
340 "Accepted values are:" \
341 " 0 = basic heap checks; " \
342 " 1 = previous level, plus basic region checks; " \
343 " 2 = previous level, plus all roots; " \
344 " 3 = previous level, plus all reachable objects; " \
345 " 4 = previous level, plus all marked objects") \
346 \
347 product(uintx, ShenandoahEvacReserve, 5, EXPERIMENTAL, \
348 "How much of (young-generation) heap to reserve for " \
349 "(young-generation) evacuations. Larger values allow GC to " \
350 "evacuate more live objects on every cycle, while leaving " \
351 "less headroom for application to allocate while GC is " \
352 "evacuating and updating references. This parameter is " \
353 "consulted at the end of marking, before selecting the " \
354 "collection set. If available memory at this time is smaller " \
355 "than the indicated reserve, the bound on collection set size is "\
356 "adjusted downward. The size of a generational mixed " \
357 "evacuation collection set (comprised of both young and old " \
358 "regions) is also bounded by this parameter. In percents of " \
359 "total (young-generation) heap size.") \
360 range(1,100) \
361 \
362 product(double, ShenandoahEvacWaste, 1.2, EXPERIMENTAL, \
363 "How much waste evacuations produce within the reserved space. " \
364 "Larger values make evacuations more resilient against " \
365 "evacuation conflicts, at expense of evacuating less on each " \
366 "GC cycle. Smaller values increase the risk of evacuation " \
367 "failures, which will trigger stop-the-world Full GC passes.") \
368 range(1.0,100.0) \
369 \
370 product(double, ShenandoahOldEvacWaste, 1.4, EXPERIMENTAL, \
371 "How much waste evacuations produce within the reserved space. " \
372 "Larger values make evacuations more resilient against " \
373 "evacuation conflicts, at expense of evacuating less on each " \
374 "GC cycle. Smaller values increase the risk of evacuation " \
375 "failures, which will trigger stop-the-world Full GC passes.") \
376 range(1.0,100.0) \
377 \
378 product(double, ShenandoahPromoEvacWaste, 1.2, EXPERIMENTAL, \
379 "How much waste promotions produce within the reserved space. " \
380 "Larger values make evacuations more resilient against " \
381 "evacuation conflicts, at expense of promoting less on each " \
382 "GC cycle. Smaller values increase the risk of evacuation " \
383 "failures, which will trigger stop-the-world Full GC passes.") \
384 range(1.0,100.0) \
385 \
386 product(uintx, ShenandoahMaxEvacLABRatio, 0, EXPERIMENTAL, \
387 "Potentially, each running thread maintains a PLAB for " \
388 "evacuating objects into old-gen memory and a GCLAB for " \
389 "evacuating objects into young-gen memory. Each time a thread " \
390 "exhausts its PLAB or GCLAB, a new local buffer is allocated. " \
391 "By default, the new buffer is twice the size of the previous " \
392 "buffer. The sizes are reset to the minimum at the start of " \
393 "each GC pass. This parameter limits the growth of evacuation " \
394 "buffer sizes to its value multiplied by the minimum buffer " \
395 "size. A higher value allows evacuation allocations to be more " \
396 "efficient because less synchronization is required by " \
397 "individual threads. However, a larger value increases the " \
398 "likelihood of evacuation failures, leading to long " \
399 "stop-the-world pauses. This is because a large value " \
400 "allows individual threads to consume large percentages of " \
401 "the total evacuation budget without necessarily effectively " \
402 "filling their local evacuation buffers with evacuated " \
403 "objects. A value of zero means no maximum size is enforced.") \
404 range(0, 1024) \
405 \
406 product(bool, ShenandoahEvacReserveOverflow, true, EXPERIMENTAL, \
407 "Allow evacuations to overflow the reserved space. Enabling it " \
408 "will make evacuations more resilient when evacuation " \
409 "reserve/waste is incorrect, at the risk that application " \
410 "runs out of memory too early.") \
411 \
412 product(uintx, ShenandoahOldEvacRatioPercent, 75, EXPERIMENTAL, \
413 "The maximum proportion of evacuation from old-gen memory, " \
414 "expressed as a percentage. The default value 75 denotes that no" \
415 "more than 75% of the collection set evacuation workload may be " \
416 "towards evacuation of old-gen heap regions. This limits both the"\
417 "promotion of aged regions and the compaction of existing old " \
418 "regions. A value of 75 denotes that the total evacuation work" \
419 "may increase to up to four times the young gen evacuation work." \
420 "A larger value allows quicker promotion and allows" \
421 "a smaller number of mixed evacuations to process " \
422 "the entire list of old-gen collection candidates at the cost " \
423 "of an increased disruption of the normal cadence of young-gen " \
424 "collections. A value of 100 allows a mixed evacuation to " \
425 "focus entirely on old-gen memory, allowing no young-gen " \
426 "regions to be collected, likely resulting in subsequent " \
427 "allocation failures because the allocation pool is not " \
428 "replenished. A value of 0 allows a mixed evacuation to" \
429 "focus entirely on young-gen memory, allowing no old-gen " \
430 "regions to be collected, likely resulting in subsequent " \
431 "promotion failures and triggering of stop-the-world full GC " \
432 "events.") \
433 range(0,100) \
434 \
435 product(uintx, ShenandoahMinYoungPercentage, 20, EXPERIMENTAL, \
436 "The minimum percentage of the heap to use for the young " \
437 "generation. Heuristics will not adjust the young generation " \
438 "to be less than this.") \
439 range(0, 100) \
440 \
441 product(uintx, ShenandoahMaxYoungPercentage, 100, EXPERIMENTAL, \
442 "The maximum percentage of the heap to use for the young " \
443 "generation. Heuristics will not adjust the young generation " \
444 "to be more than this.") \
445 range(0, 100) \
446 \
447 product(bool, ShenandoahPacing, true, EXPERIMENTAL, \
448 "Pace application allocations to give GC chance to start " \
449 "and complete before allocation failure is reached.") \
450 \
451 product(uintx, ShenandoahPacingMaxDelay, 10, EXPERIMENTAL, \
452 "Max delay for pacing application allocations. Larger values " \
453 "provide more resilience against out of memory, at expense at " \
454 "hiding the GC latencies in the allocation path. Time is in " \
455 "milliseconds. Setting it to arbitrarily large value makes " \
456 "GC effectively stall the threads indefinitely instead of going " \
457 "to degenerated or Full GC.") \
458 \
459 product(uintx, ShenandoahPacingIdleSlack, 2, EXPERIMENTAL, \
460 "How much of heap counted as non-taxable allocations during idle "\
461 "phases. Larger value makes the pacing milder when collector is " \
462 "idle, requiring less rendezvous with control thread. Lower " \
463 "value makes the pacing control less responsive to out-of-cycle " \
464 "allocs. In percent of total heap size.") \
465 range(0, 100) \
466 \
501 "that progress is determined by ShenandoahCriticalFreeThreshold") \
502 \
503 product(bool, ShenandoahImplicitGCInvokesConcurrent, false, EXPERIMENTAL, \
504 "Should internally-caused GC requests invoke concurrent cycles, " \
505 "should they do the stop-the-world (Degenerated / Full GC)? " \
506 "Many heuristics automatically enable this. This option is " \
507 "similar to global ExplicitGCInvokesConcurrent.") \
508 \
509 product(bool, ShenandoahHumongousMoves, true, DIAGNOSTIC, \
510 "Allow moving humongous regions. This makes GC more resistant " \
511 "to external fragmentation that may otherwise fail other " \
512 "humongous allocations, at the expense of higher GC copying " \
513 "costs. Currently affects stop-the-world (Full) cycle only.") \
514 \
515 product(bool, ShenandoahOOMDuringEvacALot, false, DIAGNOSTIC, \
516 "Testing: simulate OOM during evacuation.") \
517 \
518 product(bool, ShenandoahAllocFailureALot, false, DIAGNOSTIC, \
519 "Testing: make lots of artificial allocation failures.") \
520 \
521 product(uintx, ShenandoahCoalesceChance, 0, DIAGNOSTIC, \
522 "Testing: Abandon remaining mixed collections with this " \
523 "likelihood. Following each mixed collection, abandon all " \
524 "remaining mixed collection candidate regions with likelihood " \
525 "ShenandoahCoalesceChance. Abandoning a mixed collection will " \
526 "cause the old regions to be made parsable, rather than being " \
527 "evacuated.") \
528 range(0, 100) \
529 \
530 product(intx, ShenandoahMarkScanPrefetch, 32, EXPERIMENTAL, \
531 "How many objects to prefetch ahead when traversing mark bitmaps."\
532 "Set to 0 to disable prefetching.") \
533 range(0, 256) \
534 \
535 product(uintx, ShenandoahMarkLoopStride, 1000, EXPERIMENTAL, \
536 "How many items to process during one marking iteration before " \
537 "checking for cancellation, yielding, etc. Larger values improve "\
538 "marking performance at expense of responsiveness.") \
539 \
540 product(uintx, ShenandoahParallelRegionStride, 1024, EXPERIMENTAL, \
541 "How many regions to process at once during parallel region " \
542 "iteration. Affects heaps with lots of regions.") \
543 \
544 product(size_t, ShenandoahSATBBufferSize, 1 * K, EXPERIMENTAL, \
545 "Number of entries in an SATB log buffer.") \
546 range(1, max_uintx) \
547 \
548 product(uintx, ShenandoahMaxSATBBufferFlushes, 5, EXPERIMENTAL, \
549 "How many times to maximum attempt to flush SATB buffers at the " \
550 "end of concurrent marking.") \
551 \
552 product(bool, ShenandoahSATBBarrier, true, DIAGNOSTIC, \
553 "Turn on/off SATB barriers in Shenandoah") \
554 \
555 product(bool, ShenandoahIUBarrier, false, DIAGNOSTIC, \
556 "Turn on/off I-U barriers barriers in Shenandoah") \
557 \
558 product(bool, ShenandoahCardBarrier, false, DIAGNOSTIC, \
559 "Turn on/off card-marking post-write barrier in Shenandoah: " \
560 " true when ShenandoahGCMode is generational, false otherwise") \
561 \
562 product(bool, ShenandoahCASBarrier, true, DIAGNOSTIC, \
563 "Turn on/off CAS barriers in Shenandoah") \
564 \
565 product(bool, ShenandoahCloneBarrier, true, DIAGNOSTIC, \
566 "Turn on/off clone barriers in Shenandoah") \
567 \
568 product(bool, ShenandoahLoadRefBarrier, true, DIAGNOSTIC, \
569 "Turn on/off load-reference barriers in Shenandoah") \
570 \
571 product(bool, ShenandoahStackWatermarkBarrier, true, DIAGNOSTIC, \
572 "Turn on/off stack watermark barriers in Shenandoah") \
573 \
574 develop(bool, ShenandoahVerifyOptoBarriers, trueInDebug, \
575 "Verify no missing barriers in C2.") \
576 \
577 product(uintx, ShenandoahOldCompactionReserve, 8, EXPERIMENTAL, \
578 "During generational GC, prevent promotions from filling " \
579 "this number of heap regions. These regions are reserved " \
580 "for the purpose of supporting compaction of old-gen " \
581 "memory. Otherwise, old-gen memory cannot be compacted.") \
582 range(0, 128) \
583 \
584 product(bool, ShenandoahAllowOldMarkingPreemption, true, DIAGNOSTIC, \
585 "Allow young generation collections to suspend concurrent" \
586 " marking in the old generation.") \
587 \
588 product(uintx, ShenandoahAgingCyclePeriod, 1, EXPERIMENTAL, \
589 "With generational mode, increment the age of objects and" \
590 "regions each time this many young-gen GC cycles are completed.") \
591 \
592 develop(bool, ShenandoahEnableCardStats, false, \
593 "Enable statistics collection related to clean & dirty cards") \
594 \
595 develop(int, ShenandoahCardStatsLogInterval, 50, \
596 "Log cumulative card stats every so many remembered set or " \
597 "update refs scans") \
598 \
599 product(uintx, ShenandoahMinimumOldMarkTimeMs, 100, EXPERIMENTAL, \
600 "Minimum amount of time in milliseconds to run old marking " \
601 "before a young collection is allowed to run. This is intended " \
602 "to prevent starvation of the old collector. Setting this to " \
603 "0 will allow back to back young collections to run during old " \
604 "marking.") \
605 // end of GC_SHENANDOAH_FLAGS
606
607 #endif // SHARE_GC_SHENANDOAH_SHENANDOAH_GLOBALS_HPP
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