monotonic_buffer_resource: pass allocs and frees directly to upstream

src/pbrt/util/pstd.cpp

@@ -75,11 +75,10 @@ void *monotonic_buffer_resource::do_allocate(size_t bytes, size_t align) {
     // so this is tied to pbrt's current usage of them...
     CHECK(constructTID == std::this_thread::get_id());
 #endif
-
     if (bytes > block_size)
         // We've got a big allocation; let the current block be so that
         // smaller allocations have a chance at using up more of it.
-        return allocate_block(bytes)->ptr;
+        return upstream->allocate(bytes, align);
 
     if ((current_pos % align) != 0)
         current_pos += align - (current_pos % align);

src/pbrt/util/pstd.h

@@ -576,7 +576,10 @@ class alignas(64) monotonic_buffer_resource : public memory_resource {
     void *do_allocate(size_t bytes, size_t align) override;
 
     void do_deallocate(void *p, size_t bytes, size_t alignment) override {
-        // no-op
+        if (bytes > block_size)
+            // do_allocate() passes large allocations on to the upstream memory resource,
+            // so we might as well deallocate when it's possible.
+            upstream->deallocate(p, bytes);
     }
 
     bool do_is_equal(const memory_resource &other) const noexcept override {