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8308854: G1 archive region allocation may expand/shrink the heap above/below -Xms #25036

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8308854: G1 archive region allocation may expand/shrink the heap above/below -Xms #25036

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20 changes: 15 additions & 5 deletions src/hotspot/share/gc/g1/g1CollectedHeap.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -547,7 +547,6 @@ void G1CollectedHeap::dealloc_archive_regions(MemRegion range) {
assert(!is_init_completed(), "Expect to be called at JVM init time");
MemRegion reserved = _hrm.reserved();
size_t size_used = 0;
uint shrink_count = 0;

// Free the G1 regions that are within the specified range.
MutexLocker x(Heap_lock);
Expand All @@ -559,21 +558,32 @@ void G1CollectedHeap::dealloc_archive_regions(MemRegion range) {
p2i(start_address), p2i(last_address));
size_used += range.byte_size();

uint max_shrink_count = 0;
if (capacity() > MinHeapSize) {
size_t max_shrink_bytes = capacity() - MinHeapSize;
max_shrink_count = (uint)(max_shrink_bytes / G1HeapRegion::GrainBytes);
}

uint shrink_count = 0;
// Free, empty and uncommit regions with CDS archive content.
auto dealloc_archive_region = [&] (G1HeapRegion* r, bool is_last) {
guarantee(r->is_old(), "Expected old region at index %u", r->hrm_index());
_old_set.remove(r);
r->set_free();
r->set_top(r->bottom());
_hrm.shrink_at(r->hrm_index(), 1);
shrink_count++;
if (shrink_count < max_shrink_count) {
_hrm.shrink_at(r->hrm_index(), 1);
shrink_count++;
} else {
_hrm.insert_into_free_list(r);
}
};

iterate_regions_in_range(range, dealloc_archive_region);

if (shrink_count != 0) {
log_debug(gc, ergo, heap)("Attempt heap shrinking (CDS archive regions). Total size: %zuB",
G1HeapRegion::GrainWords * HeapWordSize * shrink_count);
log_debug(gc, ergo, heap)("Attempt heap shrinking (CDS archive regions). Total size: %zuB (%u Regions)",
G1HeapRegion::GrainWords * HeapWordSize * shrink_count, shrink_count);
// Explicit uncommit.
uncommit_regions(shrink_count);
}
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