In ae0ceaf ruby_dtoa was switched to use malloc instead of xmalloc, which means that consumers should be using free instead of xfree. Otherwise we will artificially shrink oldmalloc_increase_bytes.

I found this while investigating #9150

cc @nobu I'm not 100% sure this is the best approach or if we should #define MALLOC xmalloc in util.c ?

Before:

$ ./miniruby -e '10.times { 1000.times { 0.0.to_s }; GC.start(full_mark: false); puts GC.stat(:oldmalloc_increase_bytes) }'
10376
832
0
0
0
0
0
0
0
0

After:

$ ./miniruby -e '10.times { 1000.times { 0.0.to_s }; GC.start(full_mark: false); puts GC.stat(:oldmalloc_increase_bytes) }'
18376
8832
8832
8832
8832
8832
8832
8832
8832
8832