py/gc: Make GC block size be configurable.
diff --git a/py/mpconfig.h b/py/mpconfig.h
index 1f01b3d..922f865 100644
--- a/py/mpconfig.h
+++ b/py/mpconfig.h
@@ -96,6 +96,10 @@
/*****************************************************************************/
/* Memory allocation policy */
+// Number of bytes in memory allocation/GC block. Any size allocated will be
+// rounded up to be multiples of this.
+#define MICROPY_BYTES_PER_GC_BLOCK (4 * BYTES_PER_WORD)
+
// Number of words allocated (in BSS) to the GC stack (minimum is 1)
#ifndef MICROPY_ALLOC_GC_STACK_SIZE
#define MICROPY_ALLOC_GC_STACK_SIZE (64)