+;;;
+;;; FIXME: *GC-TRIGGER* seems to be denominated in bytes, not words.
+;;; And limiting it to INDEX is fairly reasonable in order to avoid
+;;; bignum arithmetic on every allocation, and to minimize the need
+;;; for thought about weird gotchas of the GC-control mechanism itself
+;;; consing as it operates. But as of sbcl-0.7.5, 512Mbytes of memory
+;;; costs $54.95 at Fry's in Dallas but cheap consumer 64-bit machines
+;;; are still over the horizon, so gratuitously limiting our heap size
+;;; to FIXNUM bytes seems fairly stupid. It'd be reasonable to
+;;; (1) allow arbitrary UNSIGNED-BYTE values of *GC-TRIGGER*, or
+;;; (2) redenominate this variable in words instead of bytes, postponing
+;;; the problem to heaps which exceed 50% of the machine's address
+;;; space, or even
+;;; (3) redemoninate this variable in CONS-sized two-word units,
+;;; allowing it to cover the entire memory space at the price of
+;;; possible loss of clarity.
+;;; (And whatever is done, it'd also be good to rename the variable so
+;;; that it's clear what unit it's denominated in.)