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/*
* Copyright (c) 2016, 2019, Red Hat, Inc. All rights reserved.
+ * Copyright Amazon.com Inc. or its affiliates. All Rights Reserved.
* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
*
* This code is free software; you can redistribute it and/or modify it
* under the terms of the GNU General Public License version 2 only, as
* published by the Free Software Foundation.
#ifndef SHARE_GC_SHENANDOAH_SHENANDOAHFREESET_HPP
#define SHARE_GC_SHENANDOAH_SHENANDOAHFREESET_HPP
#include "gc/shenandoah/shenandoahHeapRegionSet.hpp"
#include "gc/shenandoah/shenandoahHeap.hpp"
+ #include "gc/shenandoah/shenandoahSimpleBitMap.hpp"
+
+ // Each ShenandoahHeapRegion is associated with a ShenandoahFreeSetPartitionId.
+ enum class ShenandoahFreeSetPartitionId : uint8_t {
+ Mutator, // Region is in the Mutator free set: available memory is available to mutators.
+ Collector, // Region is in the Collector free set: available memory is reserved for evacuations.
+ OldCollector, // Region is in the Old Collector free set:
+ // available memory is reserved for old evacuations and for promotions..
+ NotFree // Region is in no free set: it has no available memory
+ };
+
+ // We do not maintain counts, capacity, or used for regions that are not free. Informally, if a region is NotFree, it is
+ // in no partition. NumPartitions represents the size of an array that may be indexed by Mutator or Collector.
+ #define NumPartitions (ShenandoahFreeSetPartitionId::NotFree)
+ #define IntNumPartitions int(ShenandoahFreeSetPartitionId::NotFree)
+ #define UIntNumPartitions uint(ShenandoahFreeSetPartitionId::NotFree)
+
+ // ShenandoahRegionPartitions provides an abstraction to help organize the implementation of ShenandoahFreeSet. This
+ // class implements partitioning of regions into distinct sets. Each ShenandoahHeapRegion is either in the Mutator free set,
+ // the Collector free set, or in neither free set (NotFree). When we speak of a "free partition", we mean partitions that
+ // for which the ShenandoahFreeSetPartitionId is not equal to NotFree.
+ class ShenandoahRegionPartitions {
+
+ private:
+ const ssize_t _max; // The maximum number of heap regions
+ const size_t _region_size_bytes;
+ const ShenandoahFreeSet* _free_set;
+ // For each partition, we maintain a bitmap of which regions are affiliated with his partition.
+ ShenandoahSimpleBitMap _membership[UIntNumPartitions];
+
+ // For each partition, we track an interval outside of which a region affiliated with that partition is guaranteed
+ // not to be found. This makes searches for free space more efficient. For each partition p, _leftmosts[p]
+ // represents its least index, and its _rightmosts[p] its greatest index. Empty intervals are indicated by the
+ // canonical [_max, -1].
+ ssize_t _leftmosts[UIntNumPartitions];
+ ssize_t _rightmosts[UIntNumPartitions];
+
+ // Allocation for humongous objects needs to find regions that are entirely empty. For each partion p, _leftmosts_empty[p]
+ // represents the first region belonging to this partition that is completely empty and _rightmosts_empty[p] represents the
+ // last region that is completely empty. If there is no completely empty region in this partition, this is represented
+ // by the canonical [_max, -1].
+ ssize_t _leftmosts_empty[UIntNumPartitions];
+ ssize_t _rightmosts_empty[UIntNumPartitions];
+
+ // For each partition p, _capacity[p] represents the total amount of memory within the partition at the time
+ // of the most recent rebuild, _used[p] represents the total amount of memory that has been allocated within this
+ // partition (either already allocated as of the rebuild, or allocated since the rebuild). _capacity[p] and _used[p]
+ // are denoted in bytes. Note that some regions that had been assigned to a particular partition at rebuild time
+ // may have been retired following the rebuild. The tallies for these regions are still reflected in _capacity[p]
+ // and _used[p], even though the region may have been removed from the free set.
+ size_t _capacity[UIntNumPartitions];
+ size_t _used[UIntNumPartitions];
+ size_t _region_counts[UIntNumPartitions];
+
+ // For each partition p, _left_to_right_bias is true iff allocations are normally made from lower indexed regions
+ // before higher indexed regions.
+ bool _left_to_right_bias[UIntNumPartitions];
+
+ // Shrink the intervals associated with partition when region idx is removed from this free set
+ inline void shrink_interval_if_boundary_modified(ShenandoahFreeSetPartitionId partition, ssize_t idx);
+
+ // Shrink the intervals associated with partition when regions low_idx through high_idx inclusive are removed from this free set
+ inline void shrink_interval_if_range_modifies_either_boundary(ShenandoahFreeSetPartitionId partition,
+ ssize_t low_idx, ssize_t high_idx);
+ inline void expand_interval_if_boundary_modified(ShenandoahFreeSetPartitionId partition, ssize_t idx, size_t capacity);
+
+ inline bool is_mutator_partition(ShenandoahFreeSetPartitionId p);
+ inline bool is_young_collector_partition(ShenandoahFreeSetPartitionId p);
+ inline bool is_old_collector_partition(ShenandoahFreeSetPartitionId p);
+ inline bool available_implies_empty(size_t available);
+
+ #ifndef PRODUCT
+ void dump_bitmap_row(ssize_t region_idx) const;
+ void dump_bitmap_range(ssize_t start_region_idx, ssize_t end_region_idx) const;
+ void dump_bitmap() const;
+ #endif
+ public:
+ ShenandoahRegionPartitions(size_t max_regions, ShenandoahFreeSet* free_set);
+ ~ShenandoahRegionPartitions() {}
+
+ // Remove all regions from all partitions and reset all bounds
+ void make_all_regions_unavailable();
+
+ // Set the partition id for a particular region without adjusting interval bounds or usage/capacity tallies
+ inline void raw_assign_membership(size_t idx, ShenandoahFreeSetPartitionId p) {
+ _membership[int(p)].set_bit(idx);
+ }
+
+ // Set the Mutator intervals, usage, and capacity according to arguments. Reset the Collector intervals, used, capacity
+ // to represent empty Collector free set. We use this at the end of rebuild_free_set() to avoid the overhead of making
+ // many redundant incremental adjustments to the mutator intervals as the free set is being rebuilt.
+ void establish_mutator_intervals(ssize_t mutator_leftmost, ssize_t mutator_rightmost,
+ ssize_t mutator_leftmost_empty, ssize_t mutator_rightmost_empty,
+ size_t mutator_region_count, size_t mutator_used);
+
+ // Set the OldCollector intervals, usage, and capacity according to arguments. We use this at the end of rebuild_free_set()
+ // to avoid the overhead of making many redundant incremental adjustments to the mutator intervals as the free set is being
+ // rebuilt.
+ void establish_old_collector_intervals(ssize_t old_collector_leftmost, ssize_t old_collector_rightmost,
+ ssize_t old_collector_leftmost_empty, ssize_t old_collector_rightmost_empty,
+ size_t old_collector_region_count, size_t old_collector_used);
+
+ // Retire region idx from within partition, , leaving its capacity and used as part of the original free partition's totals.
+ // Requires that region idx is in in the Mutator or Collector partitions. Hereafter, identifies this region as NotFree.
+ // Any remnant of available memory at the time of retirement is added to the original partition's total of used bytes.
+ void retire_from_partition(ShenandoahFreeSetPartitionId p, ssize_t idx, size_t used_bytes);
+
+ // Retire all regions between low_idx and high_idx inclusive from within partition. Requires that each region idx is
+ // in the same Mutator or Collector partition. Hereafter, identifies each region as NotFree. Assumes that each region
+ // is now considered fully used, since the region is presumably used to represent a humongous object.
+ void retire_range_from_partition(ShenandoahFreeSetPartitionId partition, ssize_t low_idx, ssize_t high_idx);
+
+ // Place region idx into free set which_partition. Requires that idx is currently NotFree.
+ void make_free(ssize_t idx, ShenandoahFreeSetPartitionId which_partition, size_t region_capacity);
+
+ // Place region idx into free partition new_partition, adjusting used and capacity totals for the original and new partition
+ // given that available bytes can still be allocated within this region. Requires that idx is currently not NotFree.
+ void move_from_partition_to_partition(ssize_t idx, ShenandoahFreeSetPartitionId orig_partition,
+ ShenandoahFreeSetPartitionId new_partition, size_t available);
+
+ const char* partition_membership_name(ssize_t idx) const;
+
+ // Return the index of the next available region >= start_index, or maximum_regions if not found.
+ inline ssize_t find_index_of_next_available_region(ShenandoahFreeSetPartitionId which_partition, ssize_t start_index) const;
+
+ // Return the index of the previous available region <= last_index, or -1 if not found.
+ inline ssize_t find_index_of_previous_available_region(ShenandoahFreeSetPartitionId which_partition, ssize_t last_index) const;
+
+ // Return the index of the next available cluster of cluster_size regions >= start_index, or maximum_regions if not found.
+ inline ssize_t find_index_of_next_available_cluster_of_regions(ShenandoahFreeSetPartitionId which_partition,
+ ssize_t start_index, size_t cluster_size) const;
+
+ // Return the index of the previous available cluster of cluster_size regions <= last_index, or -1 if not found.
+ inline ssize_t find_index_of_previous_available_cluster_of_regions(ShenandoahFreeSetPartitionId which_partition,
+ ssize_t last_index, size_t cluster_size) const;
+
+ inline bool in_free_set(ShenandoahFreeSetPartitionId which_partition, ssize_t idx) const {
+ return _membership[int(which_partition)].is_set(idx);
+ }
+
+ // Returns the ShenandoahFreeSetPartitionId affiliation of region idx, NotFree if this region is not currently in any partition.
+ // This does not enforce that free_set membership implies allocation capacity.
+ inline ShenandoahFreeSetPartitionId membership(ssize_t idx) const;
+
+ #ifdef ASSERT
+ // Returns true iff region idx's membership is which_partition. If which_partition represents a free set, asserts
+ // that the region has allocation capacity.
+ inline bool partition_id_matches(ssize_t idx, ShenandoahFreeSetPartitionId which_partition) const;
+ #endif
+
+ inline size_t max_regions() const { return _max; }
+
+ inline size_t region_size_bytes() const { return _region_size_bytes; };
+
+ // The following four methods return the left-most and right-most bounds on ranges of regions representing
+ // the requested set. The _empty variants represent bounds on the range that holds completely empty
+ // regions, which are required for humongous allocations and desired for "very large" allocations.
+ // if the requested which_partition is empty:
+ // leftmost() and leftmost_empty() return _max, rightmost() and rightmost_empty() return 0
+ // otherwise, expect the following:
+ // 0 <= leftmost <= leftmost_empty <= rightmost_empty <= rightmost < _max
+ inline ssize_t leftmost(ShenandoahFreeSetPartitionId which_partition) const;
+ inline ssize_t rightmost(ShenandoahFreeSetPartitionId which_partition) const;
+ ssize_t leftmost_empty(ShenandoahFreeSetPartitionId which_partition);
+ ssize_t rightmost_empty(ShenandoahFreeSetPartitionId which_partition);
+
+ inline bool is_empty(ShenandoahFreeSetPartitionId which_partition) const;
+
+ inline void increase_used(ShenandoahFreeSetPartitionId which_partition, size_t bytes);
+
+ inline void set_bias_from_left_to_right(ShenandoahFreeSetPartitionId which_partition, bool value) {
+ assert (which_partition < NumPartitions, "selected free set must be valid");
+ _left_to_right_bias[int(which_partition)] = value;
+ }
+
+ inline bool alloc_from_left_bias(ShenandoahFreeSetPartitionId which_partition) const {
+ assert (which_partition < NumPartitions, "selected free set must be valid");
+ return _left_to_right_bias[int(which_partition)];
+ }
+
+ inline size_t capacity_of(ShenandoahFreeSetPartitionId which_partition) const {
+ assert (which_partition < NumPartitions, "selected free set must be valid");
+ return _capacity[int(which_partition)];
+ }
+
+ inline size_t used_by(ShenandoahFreeSetPartitionId which_partition) const {
+ assert (which_partition < NumPartitions, "selected free set must be valid");
+ return _used[int(which_partition)];
+ }
+
+ inline size_t available_in(ShenandoahFreeSetPartitionId which_partition) const {
+ assert (which_partition < NumPartitions, "selected free set must be valid");
+ return _capacity[int(which_partition)] - _used[int(which_partition)];
+ }
+
+ inline void set_capacity_of(ShenandoahFreeSetPartitionId which_partition, size_t value) {
+ assert (which_partition < NumPartitions, "selected free set must be valid");
+ _capacity[int(which_partition)] = value;
+ }
+
+ inline void set_used_by(ShenandoahFreeSetPartitionId which_partition, size_t value) {
+ assert (which_partition < NumPartitions, "selected free set must be valid");
+ _used[int(which_partition)] = value;
+ }
+
+ inline size_t count(ShenandoahFreeSetPartitionId which_partition) const { return _region_counts[int(which_partition)]; }
+
+ // Assure leftmost, rightmost, leftmost_empty, and rightmost_empty bounds are valid for all free sets.
+ // Valid bounds honor all of the following (where max is the number of heap regions):
+ // if the set is empty, leftmost equals max and rightmost equals 0
+ // Otherwise (the set is not empty):
+ // 0 <= leftmost < max and 0 <= rightmost < max
+ // the region at leftmost is in the set
+ // the region at rightmost is in the set
+ // rightmost >= leftmost
+ // for every idx that is in the set {
+ // idx >= leftmost &&
+ // idx <= rightmost
+ // }
+ // if the set has no empty regions, leftmost_empty equals max and rightmost_empty equals 0
+ // Otherwise (the region has empty regions):
+ // 0 <= leftmost_empty < max and 0 <= rightmost_empty < max
+ // rightmost_empty >= leftmost_empty
+ // for every idx that is in the set and is empty {
+ // idx >= leftmost &&
+ // idx <= rightmost
+ // }
+ void assert_bounds() NOT_DEBUG_RETURN;
+ };
+
+ // Publicly, ShenandoahFreeSet represents memory that is available to mutator threads. The public capacity(), used(),
+ // and available() methods represent this public notion of memory that is under control of the mutator. Separately,
+ // ShenandoahFreeSet also represents memory available to garbage collection activities for compaction purposes.
+ //
+ // The Shenandoah garbage collector evacuates live objects out of specific regions that are identified as members of the
+ // collection set (cset).
+ //
+ // The ShenandoahFreeSet tries to colocate survivor objects (objects that have been evacuated at least once) at the
+ // high end of memory. New mutator allocations are taken from the low end of memory. Within the mutator's range of regions,
+ // humongous allocations are taken from the lowest addresses, and LAB (local allocation buffers) and regular shared allocations
+ // are taken from the higher address of the mutator's range of regions. This approach allows longer lasting survivor regions
+ // to congregate at the top of the heap and longer lasting humongous regions to congregate at the bottom of the heap, with
+ // short-lived frequently evacuated regions occupying the middle of the heap.
+ //
+ // Mutator and garbage collection activities tend to scramble the content of regions. Twice, during each GC pass, we rebuild
+ // the free set in an effort to restore the efficient segregation of Collector and Mutator regions:
+ //
+ // 1. At the start of evacuation, we know exactly how much memory is going to be evacuated, and this guides our
+ // sizing of the Collector free set.
+ //
+ // 2. At the end of GC, we have reclaimed all of the memory that was spanned by the cset. We rebuild here to make
+ // sure there is enough memory reserved at the high end of memory to hold the objects that might need to be evacuated
+ // during the next GC pass.
class ShenandoahFreeSet : public CHeapObj<mtGC> {
private:
ShenandoahHeap* const _heap;
- CHeapBitMap _mutator_free_bitmap;
- CHeapBitMap _collector_free_bitmap;
- size_t _max;
+ ShenandoahRegionPartitions _partitions;
+ ShenandoahHeapRegion** _trash_regions;
- // Left-most and right-most region indexes. There are no free regions outside
- // of [left-most; right-most] index intervals
- size_t _mutator_leftmost, _mutator_rightmost;
- size_t _collector_leftmost, _collector_rightmost;
+ HeapWord* allocate_aligned_plab(size_t size, ShenandoahAllocRequest& req, ShenandoahHeapRegion* r);
- size_t _capacity;
- size_t _used;
+ // Return the address of memory allocated, setting in_new_region to true iff the allocation is taken
+ // from a region that was previously empty. Return nullptr if memory could not be allocated.
+ inline HeapWord* allocate_from_partition_with_affiliation(ShenandoahAffiliation affiliation,
+ ShenandoahAllocRequest& req, bool& in_new_region);
- void assert_bounds() const NOT_DEBUG_RETURN;
+ // We re-evaluate the left-to-right allocation bias whenever _alloc_bias_weight is less than zero. Each time
+ // we allocate an object, we decrement the count of this value. Each time we re-evaluate whether to allocate
+ // from right-to-left or left-to-right, we reset the value of this counter to _InitialAllocBiasWeight.
+ ssize_t _alloc_bias_weight;
- bool is_mutator_free(size_t idx) const;
- bool is_collector_free(size_t idx) const;
+ const ssize_t INITIAL_ALLOC_BIAS_WEIGHT = 256;
+ // Increases used memory for the partition if the allocation is successful. `in_new_region` will be set
+ // if this is the first allocation in the region.
HeapWord* try_allocate_in(ShenandoahHeapRegion* region, ShenandoahAllocRequest& req, bool& in_new_region);
+
+ // While holding the heap lock, allocate memory for a single object or LAB which is to be entirely contained
+ // within a single HeapRegion as characterized by req.
+ //
+ // Precondition: !ShenandoahHeapRegion::requires_humongous(req.size())
HeapWord* allocate_single(ShenandoahAllocRequest& req, bool& in_new_region);
+
+ // While holding the heap lock, allocate memory for a humongous object which spans one or more regions that
+ // were previously empty. Regions that represent humongous objects are entirely dedicated to the humongous
+ // object. No other objects are packed into these regions.
+ //
+ // Precondition: ShenandoahHeapRegion::requires_humongous(req.size())
HeapWord* allocate_contiguous(ShenandoahAllocRequest& req);
+ // Change region r from the Mutator partition to the GC's Collector or OldCollector partition. This requires that the
+ // region is entirely empty.
+ //
+ // Typical usage: During evacuation, the GC may find it needs more memory than had been reserved at the start of evacuation to
+ // hold evacuated objects. If this occurs and memory is still available in the Mutator's free set, we will flip a region from
+ // the Mutator free set into the Collector or OldCollector free set.
void flip_to_gc(ShenandoahHeapRegion* r);
+ void flip_to_old_gc(ShenandoahHeapRegion* r);
- void recompute_bounds();
- void adjust_bounds();
- bool touches_bounds(size_t num) const;
+ // Handle allocation for mutator.
+ HeapWord* allocate_for_mutator(ShenandoahAllocRequest &req, bool &in_new_region);
- void increase_used(size_t amount);
- void clear_internal();
+ // Update allocation bias and decided whether to allocate from the left or right side of the heap.
+ void update_allocation_bias();
+
+ // Search for regions to satisfy allocation request using iterator.
+ template<typename Iter>
+ HeapWord* allocate_from_regions(Iter& iterator, ShenandoahAllocRequest &req, bool &in_new_region);
+
+ // Handle allocation for collector (for evacuation).
+ HeapWord* allocate_for_collector(ShenandoahAllocRequest& req, bool& in_new_region);
- size_t collector_count() const { return _collector_free_bitmap.count_one_bits(); }
- size_t mutator_count() const { return _mutator_free_bitmap.count_one_bits(); }
+ // Search for allocation in region with same affiliation as request, using given iterator.
+ template<typename Iter>
+ HeapWord* allocate_with_affiliation(Iter& iterator, ShenandoahAffiliation affiliation, ShenandoahAllocRequest& req, bool& in_new_region);
+ // Return true if the respective generation for this request has free regions.
+ bool can_allocate_in_new_region(const ShenandoahAllocRequest& req);
+
+ // Attempt to allocate memory for an evacuation from the mutator's partition.
+ HeapWord* try_allocate_from_mutator(ShenandoahAllocRequest& req, bool& in_new_region);
+
+ void clear_internal();
void try_recycle_trashed(ShenandoahHeapRegion *r);
- bool can_allocate_from(ShenandoahHeapRegion *r);
- size_t alloc_capacity(ShenandoahHeapRegion *r);
- bool has_no_alloc_capacity(ShenandoahHeapRegion *r);
+ // Returns true iff this region is entirely available, either because it is empty() or because it has been found to represent
+ // immediate trash and we'll be able to immediately recycle it. Note that we cannot recycle immediate trash if
+ // concurrent weak root processing is in progress.
+ inline bool can_allocate_from(ShenandoahHeapRegion *r) const;
+ inline bool can_allocate_from(size_t idx) const;
+
+ inline bool has_alloc_capacity(ShenandoahHeapRegion *r) const;
+
+ size_t transfer_empty_regions_from_collector_set_to_mutator_set(ShenandoahFreeSetPartitionId which_collector,
+ size_t max_xfer_regions,
+ size_t& bytes_transferred);
+ size_t transfer_non_empty_regions_from_collector_set_to_mutator_set(ShenandoahFreeSetPartitionId which_collector,
+ size_t max_xfer_regions,
+ size_t& bytes_transferred);
+
+
+ // Determine whether we prefer to allocate from left to right or from right to left within the OldCollector free-set.
+ void establish_old_collector_alloc_bias();
+
+ // Set max_capacity for young and old generations
+ void establish_generation_sizes(size_t young_region_count, size_t old_region_count);
+ size_t get_usable_free_words(size_t free_bytes) const;
+
+ // log status, assuming lock has already been acquired by the caller.
+ void log_status();
public:
ShenandoahFreeSet(ShenandoahHeap* heap, size_t max_regions);
+ // Public because ShenandoahRegionPartitions assertions require access.
+ inline size_t alloc_capacity(ShenandoahHeapRegion *r) const;
+ inline size_t alloc_capacity(size_t idx) const;
+
void clear();
- void rebuild();
+
+ // Examine the existing free set representation, capturing the current state into var arguments:
+ //
+ // young_cset_regions is the number of regions currently in the young cset if we are starting to evacuate, or zero
+ // old_cset_regions is the number of regions currently in the old cset if we are starting a mixed evacuation, or zero
+ // first_old_region is the index of the first region that is part of the OldCollector set
+ // last_old_region is the index of the last region that is part of the OldCollector set
+ // old_region_count is the number of regions in the OldCollector set that have memory available to be allocated
+ void prepare_to_rebuild(size_t &young_cset_regions, size_t &old_cset_regions,
+ size_t &first_old_region, size_t &last_old_region, size_t &old_region_count);
+
+ // At the end of final mark, but before we begin evacuating, heuristics calculate how much memory is required to
+ // hold the results of evacuating to young-gen and to old-gen, and have_evacuation_reserves should be true.
+ // These quantities, stored as reserves for their respective generations, are consulted prior to rebuilding
+ // the free set (ShenandoahFreeSet) in preparation for evacuation. When the free set is rebuilt, we make sure
+ // to reserve sufficient memory in the collector and old_collector sets to hold evacuations.
+ //
+ // We also rebuild the free set at the end of GC, as we prepare to idle GC until the next trigger. In this case,
+ // have_evacuation_reserves is false because we don't yet know how much memory will need to be evacuated in the
+ // next GC cycle. When have_evacuation_reserves is false, the free set rebuild operation reserves for the collector
+ // and old_collector sets based on alternative mechanisms, such as ShenandoahEvacReserve, ShenandoahOldEvacReserve, and
+ // ShenandoahOldCompactionReserve. In a future planned enhancement, the reserve for old_collector set when the
+ // evacuation reserves are unknown, is based in part on anticipated promotion as determined by analysis of live data
+ // found during the previous GC pass which is one less than the current tenure age.
+ //
+ // young_cset_regions is the number of regions currently in the young cset if we are starting to evacuate, or zero
+ // old_cset_regions is the number of regions currently in the old cset if we are starting a mixed evacuation, or zero
+ // num_old_regions is the number of old-gen regions that have available memory for further allocations (excluding old cset)
+ // have_evacuation_reserves is true iff the desired values of young-gen and old-gen evacuation reserves and old-gen
+ // promotion reserve have been precomputed (and can be obtained by invoking
+ // <generation>->get_evacuation_reserve() or old_gen->get_promoted_reserve()
+ void finish_rebuild(size_t young_cset_regions, size_t old_cset_regions, size_t num_old_regions,
+ bool have_evacuation_reserves = false);
+
+ // When a region is promoted in place, we add the region's available memory if it is greater than plab_min_size()
+ // into the old collector partition by invoking this method.
+ void add_promoted_in_place_region_to_old_collector(ShenandoahHeapRegion* region);
+
+ // Move up to cset_regions number of regions from being available to the collector to being available to the mutator.
+ //
+ // Typical usage: At the end of evacuation, when the collector no longer needs the regions that had been reserved
+ // for evacuation, invoke this to make regions available for mutator allocations.
+ void move_regions_from_collector_to_mutator(size_t cset_regions);
void recycle_trash();
- void log_status();
+ // Acquire heap lock and log status, assuming heap lock is not acquired by the caller.
+ void log_status_under_lock();
- size_t capacity() const { return _capacity; }
- size_t used() const { return _used; }
- size_t available() const {
- assert(_used <= _capacity, "must use less than capacity");
- return _capacity - _used;
+ inline size_t capacity() const { return _partitions.capacity_of(ShenandoahFreeSetPartitionId::Mutator); }
+ inline size_t used() const { return _partitions.used_by(ShenandoahFreeSetPartitionId::Mutator); }
+ inline size_t available() const {
+ assert(used() <= capacity(), "must use less than capacity");
+ return capacity() - used();
}
HeapWord* allocate(ShenandoahAllocRequest& req, bool& in_new_region);
- size_t unsafe_peek_free() const;
+ /*
+ * Internal fragmentation metric: describes how fragmented the heap regions are.
+ *
+ * It is derived as:
+ *
+ * sum(used[i]^2, i=0..k)
+ * IF = 1 - ------------------------------
+ * C * sum(used[i], i=0..k)
+ *
+ * ...where k is the number of regions in computation, C is the region capacity, and
+ * used[i] is the used space in the region.
+ *
+ * The non-linearity causes IF to be lower for the cases where the same total heap
+ * used is densely packed. For example:
+ * a) Heap is completely full => IF = 0
+ * b) Heap is half full, first 50% regions are completely full => IF = 0
+ * c) Heap is half full, each region is 50% full => IF = 1/2
+ * d) Heap is quarter full, first 50% regions are completely full => IF = 0
+ * e) Heap is quarter full, each region is 25% full => IF = 3/4
+ * f) Heap has one small object per each region => IF =~ 1
+ */
double internal_fragmentation();
+
+ /*
+ * External fragmentation metric: describes how fragmented the heap is.
+ *
+ * It is derived as:
+ *
+ * EF = 1 - largest_contiguous_free / total_free
+ *
+ * For example:
+ * a) Heap is completely empty => EF = 0
+ * b) Heap is completely full => EF = 0
+ * c) Heap is first-half full => EF = 1/2
+ * d) Heap is half full, full and empty regions interleave => EF =~ 1
+ */
double external_fragmentation();
void print_on(outputStream* out) const;
+
+ // This function places all regions that have allocation capacity into the mutator partition, or if the region
+ // is already affiliated with old, into the old collector partition, identifying regions that have no allocation
+ // capacity as NotFree. Capture the modified state of the freeset into var arguments:
+ //
+ // young_cset_regions is the number of regions currently in the young cset if we are starting to evacuate, or zero
+ // old_cset_regions is the number of regions currently in the old cset if we are starting a mixed evacuation, or zero
+ // first_old_region is the index of the first region that is part of the OldCollector set
+ // last_old_region is the index of the last region that is part of the OldCollector set
+ // old_region_count is the number of regions in the OldCollector set that have memory available to be allocated
+ void find_regions_with_alloc_capacity(size_t &young_cset_regions, size_t &old_cset_regions,
+ size_t &first_old_region, size_t &last_old_region, size_t &old_region_count);
+
+ // Ensure that Collector has at least to_reserve bytes of available memory, and OldCollector has at least old_reserve
+ // bytes of available memory. On input, old_region_count holds the number of regions already present in the
+ // OldCollector partition. Upon return, old_region_count holds the updated number of regions in the OldCollector partition.
+ void reserve_regions(size_t to_reserve, size_t old_reserve, size_t &old_region_count);
+
+ // Reserve space for evacuations, with regions reserved for old evacuations placed to the right
+ // of regions reserved of young evacuations.
+ void compute_young_and_old_reserves(size_t young_cset_regions, size_t old_cset_regions, bool have_evacuation_reserves,
+ size_t &young_reserve_result, size_t &old_reserve_result) const;
};
#endif // SHARE_GC_SHENANDOAH_SHENANDOAHFREESET_HPP
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