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8352765: G1CollectedHeap::expand_and_allocate() may fail to allocate even after heap expansion succeeds #1924

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8352765: G1CollectedHeap::expand_and_allocate() may fail to allocate even after heap expansion succeeds #1924

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38 changes: 22 additions & 16 deletions src/hotspot/share/gc/g1/g1Policy.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -338,41 +338,47 @@ uint G1Policy::calculate_young_target_length(uint desired_young_length) const {
_reserve_regions,
max_to_eat_into_reserve);

uint survivor_regions_count = _g1h->survivor_regions_count();
uint desired_eden_length = desired_young_length - survivor_regions_count;
uint allocated_eden_length = allocated_young_length - survivor_regions_count;

if (_free_regions_at_end_of_collection <= _reserve_regions) {
// Fully eat (or already eating) into the reserve, hand back at most absolute_min_length regions.
uint receiving_young = MIN3(_free_regions_at_end_of_collection,
desired_young_length,
uint receiving_eden = MIN3(_free_regions_at_end_of_collection,
desired_eden_length,
max_to_eat_into_reserve);
// Ensure that we provision for at least one Eden region.
receiving_eden = MAX2(receiving_eden, 1u);
// We could already have allocated more regions than what we could get
// above.
receiving_additional_eden = allocated_young_length < receiving_young ?
receiving_young - allocated_young_length : 0;
receiving_additional_eden = allocated_eden_length < receiving_eden ?
receiving_eden - allocated_eden_length : 0;

log_trace(gc, ergo, heap)("Young target length: Fully eat into reserve "
"receiving young %u receiving additional eden %u",
receiving_young,
receiving_additional_eden);
} else if (_free_regions_at_end_of_collection < (desired_young_length + _reserve_regions)) {
"receiving eden %u receiving additional eden %u",
receiving_eden, receiving_additional_eden);
} else if (_free_regions_at_end_of_collection < (desired_eden_length + _reserve_regions)) {
// Partially eat into the reserve, at most max_to_eat_into_reserve regions.
uint free_outside_reserve = _free_regions_at_end_of_collection - _reserve_regions;
assert(free_outside_reserve < desired_young_length,
assert(free_outside_reserve < desired_eden_length,
"must be %u %u",
free_outside_reserve, desired_young_length);
free_outside_reserve, desired_eden_length);

uint receiving_within_reserve = MIN2(desired_young_length - free_outside_reserve,
uint receiving_within_reserve = MIN2(desired_eden_length - free_outside_reserve,
max_to_eat_into_reserve);
uint receiving_young = free_outside_reserve + receiving_within_reserve;
uint receiving_eden = free_outside_reserve + receiving_within_reserve;

// Again, we could have already allocated more than we could get.
receiving_additional_eden = allocated_young_length < receiving_young ?
receiving_young - allocated_young_length : 0;
receiving_additional_eden = allocated_eden_length < receiving_eden ?
receiving_eden - allocated_eden_length : 0;

log_trace(gc, ergo, heap)("Young target length: Partially eat into reserve "
"free outside reserve %u "
"receiving within reserve %u "
"receiving young %u "
"receiving eden %u "
"receiving additional eden %u",
free_outside_reserve, receiving_within_reserve,
receiving_young, receiving_additional_eden);
receiving_eden, receiving_additional_eden);
} else {
// No need to use the reserve.
receiving_additional_eden = desired_young_length - allocated_young_length;
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