wingo pushed a commit to branch wip-whippet
in repository guile.
commit 62f4b045f8117461f1ce0a5cc426d83aea0a7748
Author: Andy Wingo <wi...@igalia.com>
AuthorDate: Tue Feb 28 22:02:49 2023 +0100
BDW supports growable heap
---
bdw.c | 32 +++++++++++++++++++++++++++-----
1 file changed, 27 insertions(+), 5 deletions(-)
diff --git a/bdw.c b/bdw.c
index 41533e1a2..d4c664eeb 100644
--- a/bdw.c
+++ b/bdw.c
@@ -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.
