512 // For this, try_reserve_heap() is called with the desired heap base addresses.
513 // A call into the os layer to allocate at a given address can return memory
514 // at a different address than requested. Still, this might be memory at a useful
515 // address. try_reserve_heap() always returns this allocated memory, as only here
516 // the criteria for a good heap are checked.
517
518 // Attempt to allocate so that we can run without base and scale (32-Bit unscaled compressed oops).
519 // Give it several tries from top of range to bottom.
520 if (aligned_heap_base_min_address + size <= (char *)UnscaledOopHeapMax) {
521
522 // Calc address range within we try to attach (range of possible start addresses).
523 char* const highest_start = align_down((char *)UnscaledOopHeapMax - size, attach_point_alignment);
524 char* const lowest_start = align_up(aligned_heap_base_min_address, attach_point_alignment);
525 try_reserve_range(highest_start, lowest_start, attach_point_alignment,
526 aligned_heap_base_min_address, (char *)UnscaledOopHeapMax, size, alignment, page_size);
527 }
528
529 // zerobased: Attempt to allocate in the lower 32G.
530 // But leave room for the compressed class pointers, which is allocated above
531 // the heap.
532 char *zerobased_max = (char *)OopEncodingHeapMax;
533 const size_t class_space = align_up(CompressedClassSpaceSize, alignment);
534 // For small heaps, save some space for compressed class pointer
535 // space so it can be decoded with no base.
536 if (UseCompressedClassPointers && !UseSharedSpaces &&
537 OopEncodingHeapMax <= KlassEncodingMetaspaceMax &&
538 (uint64_t)(aligned_heap_base_min_address + size + class_space) <= KlassEncodingMetaspaceMax) {
539 zerobased_max = (char *)OopEncodingHeapMax - class_space;
540 }
541
542 // Give it several tries from top of range to bottom.
543 if (aligned_heap_base_min_address + size <= zerobased_max && // Zerobased theoretical possible.
544 ((_base == NULL) || // No previous try succeeded.
545 (_base + size > zerobased_max))) { // Unscaled delivered an arbitrary address.
546
547 // Calc address range within we try to attach (range of possible start addresses).
548 char *const highest_start = align_down(zerobased_max - size, attach_point_alignment);
549 // Need to be careful about size being guaranteed to be less
550 // than UnscaledOopHeapMax due to type constraints.
551 char *lowest_start = aligned_heap_base_min_address;
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512 // For this, try_reserve_heap() is called with the desired heap base addresses.
513 // A call into the os layer to allocate at a given address can return memory
514 // at a different address than requested. Still, this might be memory at a useful
515 // address. try_reserve_heap() always returns this allocated memory, as only here
516 // the criteria for a good heap are checked.
517
518 // Attempt to allocate so that we can run without base and scale (32-Bit unscaled compressed oops).
519 // Give it several tries from top of range to bottom.
520 if (aligned_heap_base_min_address + size <= (char *)UnscaledOopHeapMax) {
521
522 // Calc address range within we try to attach (range of possible start addresses).
523 char* const highest_start = align_down((char *)UnscaledOopHeapMax - size, attach_point_alignment);
524 char* const lowest_start = align_up(aligned_heap_base_min_address, attach_point_alignment);
525 try_reserve_range(highest_start, lowest_start, attach_point_alignment,
526 aligned_heap_base_min_address, (char *)UnscaledOopHeapMax, size, alignment, page_size);
527 }
528
529 // zerobased: Attempt to allocate in the lower 32G.
530 // But leave room for the compressed class pointers, which is allocated above
531 // the heap.
532 // Note Lilliput: the advantages of this strategy were questionable before
533 // (since CDS=off + Compressed oops + heap large enough to suffocate us out of lower 32g
534 // is rare) and with Lilliput the encoding range drastically shrank. We may just do away
535 // with this altogether.
536 char *zerobased_max = (char *)OopEncodingHeapMax;
537 const size_t class_space = align_up(CompressedClassSpaceSize, alignment);
538 // For small heaps, save some space for compressed class pointer
539 // space so it can be decoded with no base.
540 if (UseCompressedClassPointers && !UseSharedSpaces &&
541 OopEncodingHeapMax <= KlassEncodingMetaspaceMax &&
542 (uint64_t)(aligned_heap_base_min_address + size + class_space) <= KlassEncodingMetaspaceMax) {
543 zerobased_max = (char *)OopEncodingHeapMax - class_space;
544 }
545
546 // Give it several tries from top of range to bottom.
547 if (aligned_heap_base_min_address + size <= zerobased_max && // Zerobased theoretical possible.
548 ((_base == NULL) || // No previous try succeeded.
549 (_base + size > zerobased_max))) { // Unscaled delivered an arbitrary address.
550
551 // Calc address range within we try to attach (range of possible start addresses).
552 char *const highest_start = align_down(zerobased_max - size, attach_point_alignment);
553 // Need to be careful about size being guaranteed to be less
554 // than UnscaledOopHeapMax due to type constraints.
555 char *lowest_start = aligned_heap_base_min_address;
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