1 /*
2 * Copyright (c) 2016, 2019, Red Hat, Inc. All rights reserved.
3 * Copyright Amazon.com Inc. or its affiliates. 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,
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19 *
20 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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24 */
25
26 #ifndef SHARE_GC_SHENANDOAH_SHENANDOAHFREESET_HPP
27 #define SHARE_GC_SHENANDOAH_SHENANDOAHFREESET_HPP
28
29 #include "gc/shenandoah/shenandoahHeapRegionSet.hpp"
30 #include "gc/shenandoah/shenandoahHeap.hpp"
31 #include "gc/shenandoah/shenandoahSimpleBitMap.hpp"
32
33 // Each ShenandoahHeapRegion is associated with a ShenandoahFreeSetPartitionId.
34 enum class ShenandoahFreeSetPartitionId : uint8_t {
35 Mutator, // Region is in the Mutator free set: available memory is available to mutators.
36 Collector, // Region is in the Collector free set: available memory is reserved for evacuations.
37 OldCollector, // Region is in the Old Collector free set:
38 // available memory is reserved for old evacuations and for promotions..
39 NotFree // Region is in no free set: it has no available memory
40 };
41
42 // We do not maintain counts, capacity, or used for regions that are not free. Informally, if a region is NotFree, it is
43 // in no partition. NumPartitions represents the size of an array that may be indexed by Mutator or Collector.
44 #define NumPartitions (ShenandoahFreeSetPartitionId::NotFree)
45 #define IntNumPartitions int(ShenandoahFreeSetPartitionId::NotFree)
46 #define UIntNumPartitions uint(ShenandoahFreeSetPartitionId::NotFree)
47
48 // ShenandoahRegionPartitions provides an abstraction to help organize the implementation of ShenandoahFreeSet. This
49 // class implements partitioning of regions into distinct sets. Each ShenandoahHeapRegion is either in the Mutator free set,
50 // the Collector free set, or in neither free set (NotFree). When we speak of a "free partition", we mean partitions that
51 // for which the ShenandoahFreeSetPartitionId is not equal to NotFree.
52 class ShenandoahRegionPartitions {
53
54 private:
55 const ssize_t _max; // The maximum number of heap regions
56 const size_t _region_size_bytes;
57 const ShenandoahFreeSet* _free_set;
58 // For each partition, we maintain a bitmap of which regions are affiliated with his partition.
59 ShenandoahSimpleBitMap _membership[UIntNumPartitions];
60
61 // For each partition, we track an interval outside of which a region affiliated with that partition is guaranteed
62 // not to be found. This makes searches for free space more efficient. For each partition p, _leftmosts[p]
63 // represents its least index, and its _rightmosts[p] its greatest index. Empty intervals are indicated by the
64 // canonical [_max, -1].
65 ssize_t _leftmosts[UIntNumPartitions];
66 ssize_t _rightmosts[UIntNumPartitions];
67
68 // Allocation for humongous objects needs to find regions that are entirely empty. For each partion p, _leftmosts_empty[p]
69 // represents the first region belonging to this partition that is completely empty and _rightmosts_empty[p] represents the
70 // last region that is completely empty. If there is no completely empty region in this partition, this is represented
71 // by the canonical [_max, -1].
72 ssize_t _leftmosts_empty[UIntNumPartitions];
73 ssize_t _rightmosts_empty[UIntNumPartitions];
74
75 // For each partition p, _capacity[p] represents the total amount of memory within the partition at the time
76 // of the most recent rebuild, _used[p] represents the total amount of memory that has been allocated within this
77 // partition (either already allocated as of the rebuild, or allocated since the rebuild). _capacity[p] and _used[p]
78 // are denoted in bytes. Note that some regions that had been assigned to a particular partition at rebuild time
79 // may have been retired following the rebuild. The tallies for these regions are still reflected in _capacity[p]
80 // and _used[p], even though the region may have been removed from the free set.
81 size_t _capacity[UIntNumPartitions];
82 size_t _used[UIntNumPartitions];
83 size_t _region_counts[UIntNumPartitions];
84
85 // For each partition p, _left_to_right_bias is true iff allocations are normally made from lower indexed regions
86 // before higher indexed regions.
87 bool _left_to_right_bias[UIntNumPartitions];
88
89 // Shrink the intervals associated with partition when region idx is removed from this free set
90 inline void shrink_interval_if_boundary_modified(ShenandoahFreeSetPartitionId partition, ssize_t idx);
91
92 // Shrink the intervals associated with partition when regions low_idx through high_idx inclusive are removed from this free set
93 inline void shrink_interval_if_range_modifies_either_boundary(ShenandoahFreeSetPartitionId partition,
94 ssize_t low_idx, ssize_t high_idx);
95 inline void expand_interval_if_boundary_modified(ShenandoahFreeSetPartitionId partition, ssize_t idx, size_t capacity);
96
97 inline bool is_mutator_partition(ShenandoahFreeSetPartitionId p);
98 inline bool is_young_collector_partition(ShenandoahFreeSetPartitionId p);
99 inline bool is_old_collector_partition(ShenandoahFreeSetPartitionId p);
100 inline bool available_implies_empty(size_t available);
101
102 #ifndef PRODUCT
103 void dump_bitmap_row(ssize_t region_idx) const;
104 void dump_bitmap_range(ssize_t start_region_idx, ssize_t end_region_idx) const;
105 void dump_bitmap() const;
106 #endif
107 public:
108 ShenandoahRegionPartitions(size_t max_regions, ShenandoahFreeSet* free_set);
109 ~ShenandoahRegionPartitions() {}
110
111 // Remove all regions from all partitions and reset all bounds
112 void make_all_regions_unavailable();
113
114 // Set the partition id for a particular region without adjusting interval bounds or usage/capacity tallies
115 inline void raw_assign_membership(size_t idx, ShenandoahFreeSetPartitionId p) {
116 _membership[int(p)].set_bit(idx);
117 }
118
119 // Set the Mutator intervals, usage, and capacity according to arguments. Reset the Collector intervals, used, capacity
120 // to represent empty Collector free set. We use this at the end of rebuild_free_set() to avoid the overhead of making
121 // many redundant incremental adjustments to the mutator intervals as the free set is being rebuilt.
122 void establish_mutator_intervals(ssize_t mutator_leftmost, ssize_t mutator_rightmost,
123 ssize_t mutator_leftmost_empty, ssize_t mutator_rightmost_empty,
124 size_t mutator_region_count, size_t mutator_used);
125
126 // Set the OldCollector intervals, usage, and capacity according to arguments. We use this at the end of rebuild_free_set()
127 // to avoid the overhead of making many redundant incremental adjustments to the mutator intervals as the free set is being
128 // rebuilt.
129 void establish_old_collector_intervals(ssize_t old_collector_leftmost, ssize_t old_collector_rightmost,
130 ssize_t old_collector_leftmost_empty, ssize_t old_collector_rightmost_empty,
131 size_t old_collector_region_count, size_t old_collector_used);
132
133 // Retire region idx from within partition, , leaving its capacity and used as part of the original free partition's totals.
134 // Requires that region idx is in in the Mutator or Collector partitions. Hereafter, identifies this region as NotFree.
135 // Any remnant of available memory at the time of retirement is added to the original partition's total of used bytes.
136 void retire_from_partition(ShenandoahFreeSetPartitionId p, ssize_t idx, size_t used_bytes);
137
138 // Retire all regions between low_idx and high_idx inclusive from within partition. Requires that each region idx is
139 // in the same Mutator or Collector partition. Hereafter, identifies each region as NotFree. Assumes that each region
140 // is now considered fully used, since the region is presumably used to represent a humongous object.
141 void retire_range_from_partition(ShenandoahFreeSetPartitionId partition, ssize_t low_idx, ssize_t high_idx);
142
143 // Place region idx into free set which_partition. Requires that idx is currently NotFree.
144 void make_free(ssize_t idx, ShenandoahFreeSetPartitionId which_partition, size_t region_capacity);
145
146 // Place region idx into free partition new_partition, adjusting used and capacity totals for the original and new partition
147 // given that available bytes can still be allocated within this region. Requires that idx is currently not NotFree.
148 void move_from_partition_to_partition(ssize_t idx, ShenandoahFreeSetPartitionId orig_partition,
149 ShenandoahFreeSetPartitionId new_partition, size_t available);
150
151 const char* partition_membership_name(ssize_t idx) const;
152
153 // Return the index of the next available region >= start_index, or maximum_regions if not found.
154 inline ssize_t find_index_of_next_available_region(ShenandoahFreeSetPartitionId which_partition, ssize_t start_index) const;
155
156 // Return the index of the previous available region <= last_index, or -1 if not found.
157 inline ssize_t find_index_of_previous_available_region(ShenandoahFreeSetPartitionId which_partition, ssize_t last_index) const;
158
159 // Return the index of the next available cluster of cluster_size regions >= start_index, or maximum_regions if not found.
160 inline ssize_t find_index_of_next_available_cluster_of_regions(ShenandoahFreeSetPartitionId which_partition,
161 ssize_t start_index, size_t cluster_size) const;
162
163 // Return the index of the previous available cluster of cluster_size regions <= last_index, or -1 if not found.
164 inline ssize_t find_index_of_previous_available_cluster_of_regions(ShenandoahFreeSetPartitionId which_partition,
165 ssize_t last_index, size_t cluster_size) const;
166
167 inline bool in_free_set(ShenandoahFreeSetPartitionId which_partition, ssize_t idx) const {
168 return _membership[int(which_partition)].is_set(idx);
169 }
170
171 // Returns the ShenandoahFreeSetPartitionId affiliation of region idx, NotFree if this region is not currently in any partition.
172 // This does not enforce that free_set membership implies allocation capacity.
173 inline ShenandoahFreeSetPartitionId membership(ssize_t idx) const;
174
175 #ifdef ASSERT
176 // Returns true iff region idx's membership is which_partition. If which_partition represents a free set, asserts
177 // that the region has allocation capacity.
178 inline bool partition_id_matches(ssize_t idx, ShenandoahFreeSetPartitionId which_partition) const;
179 #endif
180
181 inline size_t max_regions() const { return _max; }
182
183 inline size_t region_size_bytes() const { return _region_size_bytes; };
184
185 // The following four methods return the left-most and right-most bounds on ranges of regions representing
186 // the requested set. The _empty variants represent bounds on the range that holds completely empty
187 // regions, which are required for humongous allocations and desired for "very large" allocations.
188 // if the requested which_partition is empty:
189 // leftmost() and leftmost_empty() return _max, rightmost() and rightmost_empty() return 0
190 // otherwise, expect the following:
191 // 0 <= leftmost <= leftmost_empty <= rightmost_empty <= rightmost < _max
192 inline ssize_t leftmost(ShenandoahFreeSetPartitionId which_partition) const;
193 inline ssize_t rightmost(ShenandoahFreeSetPartitionId which_partition) const;
194 ssize_t leftmost_empty(ShenandoahFreeSetPartitionId which_partition);
195 ssize_t rightmost_empty(ShenandoahFreeSetPartitionId which_partition);
196
197 inline bool is_empty(ShenandoahFreeSetPartitionId which_partition) const;
198
199 inline void increase_used(ShenandoahFreeSetPartitionId which_partition, size_t bytes);
200
201 inline void set_bias_from_left_to_right(ShenandoahFreeSetPartitionId which_partition, bool value) {
202 assert (which_partition < NumPartitions, "selected free set must be valid");
203 _left_to_right_bias[int(which_partition)] = value;
204 }
205
206 inline bool alloc_from_left_bias(ShenandoahFreeSetPartitionId which_partition) const {
207 assert (which_partition < NumPartitions, "selected free set must be valid");
208 return _left_to_right_bias[int(which_partition)];
209 }
210
211 inline size_t capacity_of(ShenandoahFreeSetPartitionId which_partition) const {
212 assert (which_partition < NumPartitions, "selected free set must be valid");
213 return _capacity[int(which_partition)];
214 }
215
216 inline size_t used_by(ShenandoahFreeSetPartitionId which_partition) const {
217 assert (which_partition < NumPartitions, "selected free set must be valid");
218 return _used[int(which_partition)];
219 }
220
221 inline size_t available_in(ShenandoahFreeSetPartitionId which_partition) const {
222 assert (which_partition < NumPartitions, "selected free set must be valid");
223 return _capacity[int(which_partition)] - _used[int(which_partition)];
224 }
225
226 inline void set_capacity_of(ShenandoahFreeSetPartitionId which_partition, size_t value) {
227 assert (which_partition < NumPartitions, "selected free set must be valid");
228 _capacity[int(which_partition)] = value;
229 }
230
231 inline void set_used_by(ShenandoahFreeSetPartitionId which_partition, size_t value) {
232 assert (which_partition < NumPartitions, "selected free set must be valid");
233 _used[int(which_partition)] = value;
234 }
235
236 inline size_t count(ShenandoahFreeSetPartitionId which_partition) const { return _region_counts[int(which_partition)]; }
237
238 // Assure leftmost, rightmost, leftmost_empty, and rightmost_empty bounds are valid for all free sets.
239 // Valid bounds honor all of the following (where max is the number of heap regions):
240 // if the set is empty, leftmost equals max and rightmost equals 0
241 // Otherwise (the set is not empty):
242 // 0 <= leftmost < max and 0 <= rightmost < max
243 // the region at leftmost is in the set
244 // the region at rightmost is in the set
245 // rightmost >= leftmost
246 // for every idx that is in the set {
247 // idx >= leftmost &&
248 // idx <= rightmost
249 // }
250 // if the set has no empty regions, leftmost_empty equals max and rightmost_empty equals 0
251 // Otherwise (the region has empty regions):
252 // 0 <= leftmost_empty < max and 0 <= rightmost_empty < max
253 // rightmost_empty >= leftmost_empty
254 // for every idx that is in the set and is empty {
255 // idx >= leftmost &&
256 // idx <= rightmost
257 // }
258 void assert_bounds() NOT_DEBUG_RETURN;
259 };
260
261 // Publicly, ShenandoahFreeSet represents memory that is available to mutator threads. The public capacity(), used(),
262 // and available() methods represent this public notion of memory that is under control of the mutator. Separately,
263 // ShenandoahFreeSet also represents memory available to garbage collection activities for compaction purposes.
264 //
265 // The Shenandoah garbage collector evacuates live objects out of specific regions that are identified as members of the
266 // collection set (cset).
267 //
268 // The ShenandoahFreeSet tries to colocate survivor objects (objects that have been evacuated at least once) at the
269 // high end of memory. New mutator allocations are taken from the low end of memory. Within the mutator's range of regions,
270 // humongous allocations are taken from the lowest addresses, and LAB (local allocation buffers) and regular shared allocations
271 // are taken from the higher address of the mutator's range of regions. This approach allows longer lasting survivor regions
272 // to congregate at the top of the heap and longer lasting humongous regions to congregate at the bottom of the heap, with
273 // short-lived frequently evacuated regions occupying the middle of the heap.
274 //
275 // Mutator and garbage collection activities tend to scramble the content of regions. Twice, during each GC pass, we rebuild
276 // the free set in an effort to restore the efficient segregation of Collector and Mutator regions:
277 //
278 // 1. At the start of evacuation, we know exactly how much memory is going to be evacuated, and this guides our
279 // sizing of the Collector free set.
280 //
281 // 2. At the end of GC, we have reclaimed all of the memory that was spanned by the cset. We rebuild here to make
282 // sure there is enough memory reserved at the high end of memory to hold the objects that might need to be evacuated
283 // during the next GC pass.
284
285 class ShenandoahFreeSet : public CHeapObj<mtGC> {
286 private:
287 ShenandoahHeap* const _heap;
288 ShenandoahRegionPartitions _partitions;
289 ShenandoahHeapRegion** _trash_regions;
290
291 HeapWord* allocate_aligned_plab(size_t size, ShenandoahAllocRequest& req, ShenandoahHeapRegion* r);
292
293 // Return the address of memory allocated, setting in_new_region to true iff the allocation is taken
294 // from a region that was previously empty. Return nullptr if memory could not be allocated.
295 inline HeapWord* allocate_from_partition_with_affiliation(ShenandoahAffiliation affiliation,
296 ShenandoahAllocRequest& req, bool& in_new_region);
297
298 // We re-evaluate the left-to-right allocation bias whenever _alloc_bias_weight is less than zero. Each time
299 // we allocate an object, we decrement the count of this value. Each time we re-evaluate whether to allocate
300 // from right-to-left or left-to-right, we reset the value of this counter to _InitialAllocBiasWeight.
301 ssize_t _alloc_bias_weight;
302
303 const ssize_t INITIAL_ALLOC_BIAS_WEIGHT = 256;
304
305 // Increases used memory for the partition if the allocation is successful. `in_new_region` will be set
306 // if this is the first allocation in the region.
307 HeapWord* try_allocate_in(ShenandoahHeapRegion* region, ShenandoahAllocRequest& req, bool& in_new_region);
308
309 // While holding the heap lock, allocate memory for a single object or LAB which is to be entirely contained
310 // within a single HeapRegion as characterized by req.
311 //
312 // Precondition: !ShenandoahHeapRegion::requires_humongous(req.size())
313 HeapWord* allocate_single(ShenandoahAllocRequest& req, bool& in_new_region);
314
315 // While holding the heap lock, allocate memory for a humongous object which spans one or more regions that
316 // were previously empty. Regions that represent humongous objects are entirely dedicated to the humongous
317 // object. No other objects are packed into these regions.
318 //
319 // Precondition: ShenandoahHeapRegion::requires_humongous(req.size())
320 HeapWord* allocate_contiguous(ShenandoahAllocRequest& req);
321
322 // Change region r from the Mutator partition to the GC's Collector or OldCollector partition. This requires that the
323 // region is entirely empty.
324 //
325 // Typical usage: During evacuation, the GC may find it needs more memory than had been reserved at the start of evacuation to
326 // hold evacuated objects. If this occurs and memory is still available in the Mutator's free set, we will flip a region from
327 // the Mutator free set into the Collector or OldCollector free set.
328 void flip_to_gc(ShenandoahHeapRegion* r);
329 void flip_to_old_gc(ShenandoahHeapRegion* r);
330
331 // Handle allocation for mutator.
332 HeapWord* allocate_for_mutator(ShenandoahAllocRequest &req, bool &in_new_region);
333
334 // Update allocation bias and decided whether to allocate from the left or right side of the heap.
335 void update_allocation_bias();
336
337 // Search for regions to satisfy allocation request using iterator.
338 template<typename Iter>
339 HeapWord* allocate_from_regions(Iter& iterator, ShenandoahAllocRequest &req, bool &in_new_region);
340
341 // Handle allocation for collector (for evacuation).
342 HeapWord* allocate_for_collector(ShenandoahAllocRequest& req, bool& in_new_region);
343
344 // Search for allocation in region with same affiliation as request, using given iterator.
345 template<typename Iter>
346 HeapWord* allocate_with_affiliation(Iter& iterator, ShenandoahAffiliation affiliation, ShenandoahAllocRequest& req, bool& in_new_region);
347
348 // Return true if the respective generation for this request has free regions.
349 bool can_allocate_in_new_region(const ShenandoahAllocRequest& req);
350
351 // Attempt to allocate memory for an evacuation from the mutator's partition.
352 HeapWord* try_allocate_from_mutator(ShenandoahAllocRequest& req, bool& in_new_region);
353
354 void clear_internal();
355 void try_recycle_trashed(ShenandoahHeapRegion *r);
356
357 // Returns true iff this region is entirely available, either because it is empty() or because it has been found to represent
358 // immediate trash and we'll be able to immediately recycle it. Note that we cannot recycle immediate trash if
359 // concurrent weak root processing is in progress.
360 inline bool can_allocate_from(ShenandoahHeapRegion *r) const;
361 inline bool can_allocate_from(size_t idx) const;
362
363 inline bool has_alloc_capacity(ShenandoahHeapRegion *r) const;
364
365 size_t transfer_empty_regions_from_collector_set_to_mutator_set(ShenandoahFreeSetPartitionId which_collector,
366 size_t max_xfer_regions,
367 size_t& bytes_transferred);
368 size_t transfer_non_empty_regions_from_collector_set_to_mutator_set(ShenandoahFreeSetPartitionId which_collector,
369 size_t max_xfer_regions,
370 size_t& bytes_transferred);
371
372
373 // Determine whether we prefer to allocate from left to right or from right to left within the OldCollector free-set.
374 void establish_old_collector_alloc_bias();
375
376 // Set max_capacity for young and old generations
377 void establish_generation_sizes(size_t young_region_count, size_t old_region_count);
378 size_t get_usable_free_words(size_t free_bytes) const;
379
380 // log status, assuming lock has already been acquired by the caller.
381 void log_status();
382
383 public:
384 ShenandoahFreeSet(ShenandoahHeap* heap, size_t max_regions);
385
386 // Public because ShenandoahRegionPartitions assertions require access.
387 inline size_t alloc_capacity(ShenandoahHeapRegion *r) const;
388 inline size_t alloc_capacity(size_t idx) const;
389
390 void clear();
391
392 // Examine the existing free set representation, capturing the current state into var arguments:
393 //
394 // young_cset_regions is the number of regions currently in the young cset if we are starting to evacuate, or zero
395 // old_cset_regions is the number of regions currently in the old cset if we are starting a mixed evacuation, or zero
396 // first_old_region is the index of the first region that is part of the OldCollector set
397 // last_old_region is the index of the last region that is part of the OldCollector set
398 // old_region_count is the number of regions in the OldCollector set that have memory available to be allocated
399 void prepare_to_rebuild(size_t &young_cset_regions, size_t &old_cset_regions,
400 size_t &first_old_region, size_t &last_old_region, size_t &old_region_count);
401
402 // At the end of final mark, but before we begin evacuating, heuristics calculate how much memory is required to
403 // hold the results of evacuating to young-gen and to old-gen, and have_evacuation_reserves should be true.
404 // These quantities, stored as reserves for their respective generations, are consulted prior to rebuilding
405 // the free set (ShenandoahFreeSet) in preparation for evacuation. When the free set is rebuilt, we make sure
406 // to reserve sufficient memory in the collector and old_collector sets to hold evacuations.
407 //
408 // We also rebuild the free set at the end of GC, as we prepare to idle GC until the next trigger. In this case,
409 // have_evacuation_reserves is false because we don't yet know how much memory will need to be evacuated in the
410 // next GC cycle. When have_evacuation_reserves is false, the free set rebuild operation reserves for the collector
411 // and old_collector sets based on alternative mechanisms, such as ShenandoahEvacReserve, ShenandoahOldEvacReserve, and
412 // ShenandoahOldCompactionReserve. In a future planned enhancement, the reserve for old_collector set when the
413 // evacuation reserves are unknown, is based in part on anticipated promotion as determined by analysis of live data
414 // found during the previous GC pass which is one less than the current tenure age.
415 //
416 // young_cset_regions is the number of regions currently in the young cset if we are starting to evacuate, or zero
417 // old_cset_regions is the number of regions currently in the old cset if we are starting a mixed evacuation, or zero
418 // num_old_regions is the number of old-gen regions that have available memory for further allocations (excluding old cset)
419 // have_evacuation_reserves is true iff the desired values of young-gen and old-gen evacuation reserves and old-gen
420 // promotion reserve have been precomputed (and can be obtained by invoking
421 // <generation>->get_evacuation_reserve() or old_gen->get_promoted_reserve()
422 void finish_rebuild(size_t young_cset_regions, size_t old_cset_regions, size_t num_old_regions,
423 bool have_evacuation_reserves = false);
424
425 // When a region is promoted in place, we add the region's available memory if it is greater than plab_min_size()
426 // into the old collector partition by invoking this method.
427 void add_promoted_in_place_region_to_old_collector(ShenandoahHeapRegion* region);
428
429 // Move up to cset_regions number of regions from being available to the collector to being available to the mutator.
430 //
431 // Typical usage: At the end of evacuation, when the collector no longer needs the regions that had been reserved
432 // for evacuation, invoke this to make regions available for mutator allocations.
433 void move_regions_from_collector_to_mutator(size_t cset_regions);
434
435 void recycle_trash();
436
437 // Acquire heap lock and log status, assuming heap lock is not acquired by the caller.
438 void log_status_under_lock();
439
440 inline size_t capacity() const { return _partitions.capacity_of(ShenandoahFreeSetPartitionId::Mutator); }
441 inline size_t used() const { return _partitions.used_by(ShenandoahFreeSetPartitionId::Mutator); }
442 inline size_t available() const {
443 assert(used() <= capacity(), "must use less than capacity");
444 return capacity() - used();
445 }
446
447 HeapWord* allocate(ShenandoahAllocRequest& req, bool& in_new_region);
448
449 /*
450 * Internal fragmentation metric: describes how fragmented the heap regions are.
451 *
452 * It is derived as:
453 *
454 * sum(used[i]^2, i=0..k)
455 * IF = 1 - ------------------------------
456 * C * sum(used[i], i=0..k)
457 *
458 * ...where k is the number of regions in computation, C is the region capacity, and
459 * used[i] is the used space in the region.
460 *
461 * The non-linearity causes IF to be lower for the cases where the same total heap
462 * used is densely packed. For example:
463 * a) Heap is completely full => IF = 0
464 * b) Heap is half full, first 50% regions are completely full => IF = 0
465 * c) Heap is half full, each region is 50% full => IF = 1/2
466 * d) Heap is quarter full, first 50% regions are completely full => IF = 0
467 * e) Heap is quarter full, each region is 25% full => IF = 3/4
468 * f) Heap has one small object per each region => IF =~ 1
469 */
470 double internal_fragmentation();
471
472 /*
473 * External fragmentation metric: describes how fragmented the heap is.
474 *
475 * It is derived as:
476 *
477 * EF = 1 - largest_contiguous_free / total_free
478 *
479 * For example:
480 * a) Heap is completely empty => EF = 0
481 * b) Heap is completely full => EF = 0
482 * c) Heap is first-half full => EF = 1/2
483 * d) Heap is half full, full and empty regions interleave => EF =~ 1
484 */
485 double external_fragmentation();
486
487 void print_on(outputStream* out) const;
488
489 // This function places all regions that have allocation capacity into the mutator partition, or if the region
490 // is already affiliated with old, into the old collector partition, identifying regions that have no allocation
491 // capacity as NotFree. Capture the modified state of the freeset into var arguments:
492 //
493 // young_cset_regions is the number of regions currently in the young cset if we are starting to evacuate, or zero
494 // old_cset_regions is the number of regions currently in the old cset if we are starting a mixed evacuation, or zero
495 // first_old_region is the index of the first region that is part of the OldCollector set
496 // last_old_region is the index of the last region that is part of the OldCollector set
497 // old_region_count is the number of regions in the OldCollector set that have memory available to be allocated
498 void find_regions_with_alloc_capacity(size_t &young_cset_regions, size_t &old_cset_regions,
499 size_t &first_old_region, size_t &last_old_region, size_t &old_region_count);
500
501 // Ensure that Collector has at least to_reserve bytes of available memory, and OldCollector has at least old_reserve
502 // bytes of available memory. On input, old_region_count holds the number of regions already present in the
503 // OldCollector partition. Upon return, old_region_count holds the updated number of regions in the OldCollector partition.
504 void reserve_regions(size_t to_reserve, size_t old_reserve, size_t &old_region_count);
505
506 // Reserve space for evacuations, with regions reserved for old evacuations placed to the right
507 // of regions reserved of young evacuations.
508 void compute_young_and_old_reserves(size_t young_cset_regions, size_t old_cset_regions, bool have_evacuation_reserves,
509 size_t &young_reserve_result, size_t &old_reserve_result) const;
510 };
511
512 #endif // SHARE_GC_SHENANDOAH_SHENANDOAHFREESET_HPP