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BDW supports growable heap

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This commit is contained in:
Andy Wingo 2023-02-28 22:02:49 +01:00
parent 51168fd96e
commit 62f4b045f8
1 changed files with 27 additions and 5 deletions
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32
bdw.c
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@ -248,13 +248,35 @@ int gc_init(const struct gc_options *options, struct gc_stack_addr *stack_base,
if (!options) options = gc_allocate_options();
// GC_full_freq = 30;
// GC_free_space_divisor = 16;
// GC_enable_incremental();
// Ignore stack base for main thread.
GC_set_max_heap_size(options->common.heap_size);
switch (options->common.heap_size_policy) {
case GC_HEAP_SIZE_FIXED:
GC_set_max_heap_size(options->common.heap_size);
break;
case GC_HEAP_SIZE_GROWABLE: {
if (options->common.maximum_heap_size)
GC_set_max_heap_size(options->common.maximum_heap_size);
// BDW uses a pretty weird heap-sizing heuristic:
//
// heap-size = live-data * (1 + (2 / GC_free_space_divisor))
// heap-size-multiplier = heap-size/live-data = 1 + 2/GC_free_space_divisor
// GC_free_space_divisor = 2/(heap-size-multiplier-1)
//
// (Assumption: your heap is mostly "composite", i.e. not
// "atomic". See bdw's alloc.c:min_bytes_allocd.)
double fsd = 2.0/(options->common.heap_size_multiplier - 1);
// But, the divisor is an integer. WTF. This caps the effective
// maximum heap multiplier at 3. Oh well.
GC_set_free_space_divisor(fsd + 0.51);
break;
}
case GC_HEAP_SIZE_ADAPTIVE:
default:
fprintf(stderr, "adaptive heap sizing unsupported by bdw-gc\n");
return 0;
}
// Not part of 7.3, sigh. Have to set an env var.
// GC_set_markers_count(options->common.parallelism);
char markers[21] = {0,}; // 21 bytes enough for 2**64 in decimal + NUL.