[Guile-commits] 07/09: mmc: Grow the heap if collection fails to find space for large alloc

[Andy Wingo]

wingo pushed a commit to branch wip-whippet
in repository guile.

commit b794e4663505a98d728943cb21edc735cd7d174b
Author: Andy Wingo <wingo@igalia.com>
AuthorDate: Fri May 16 22:01:55 2025 +0200

    mmc: Grow the heap if collection fails to find space for large alloc
    
    For a pending large allocation, we will try to page out blocks from the
    nofl space.  However sometimes we are not able to do so, especially if
    evacuation is unavailable, as in a heap-conservative configuration.  In
    that case, if the heap is growable, grow the heap after GC if there are
    still bytes pending to page out.
---
 src/mmc.c | 18 ++++++++++++++++++
 1 file changed, 18 insertions(+)

diff --git a/src/mmc.c b/src/mmc.c
index 375548701..79e6a709a 100644
--- a/src/mmc.c
+++ b/src/mmc.c
@@ -531,6 +531,23 @@ compute_progress(struct gc_heap *heap, uintptr_t 
allocation_since_last_gc) {
   return allocation_since_last_gc > nofl_space_fragmentation(nofl);
 }
 
+static void
+grow_heap_for_large_allocation_if_necessary(struct gc_heap *heap,
+                                            enum gc_collection_kind gc_kind,
+                                            int progress)
+{
+  if (progress || heap->sizer.policy == GC_HEAP_SIZE_FIXED)
+    return;
+
+  struct nofl_space *nofl = heap_nofl_space(heap);
+  if (nofl_space_shrink (nofl, 0))
+    return;
+
+  ssize_t pending = nofl_space_request_release_memory(nofl, 0);
+  GC_ASSERT (pending > 0);
+  resize_heap(heap, heap->size + pending);
+}
+
 static int
 compute_success(struct gc_heap *heap, enum gc_collection_kind gc_kind,
                 int progress) {
@@ -833,6 +850,7 @@ collect(struct gc_mutator *mut, enum gc_collection_kind 
requested_kind) {
   DEBUG("--- total live bytes estimate: %zu\n", live_bytes_estimate);
   gc_heap_sizer_on_gc(heap->sizer, heap->size, live_bytes_estimate, pause_ns,
                       resize_heap);
+  grow_heap_for_large_allocation_if_necessary(heap, gc_kind, progress);
   heap->size_at_last_gc = heap->size;
   HEAP_EVENT(heap, restarting_mutators);
   allow_mutators_to_continue(heap);