> 1. How do I tell how much heap space is available in a currently
> running SBCL?
There's no exported interface for that, though you can get at it
through some symbols in the internal SB-VM package. I think Cyrus
Harmon posted a patch last summer for adding this information into the
output of ROOM.
> 2. Is there a command-line switch to control the heap size? I looked
> in the manual but didn't see anything? Maybe the size is
> determined at compile-time, so I have to rebuild from source? If
> so, what do I set?
Tweak dynamic-space-start / dynamic-space-end in
src/compiler/x86/parms.lisp and recompile.
> 3. What is the maximum possible heap size, for both 32 and 64-bit x86
That will depend on how big a free contiguous memory area you can
find, which is somewhat out of SBCL's hands. You can probably get
something around 2GB on x86. I have no idea of what the practical
x86-64 upper limit is, but it should be large enough to not matter.
There are some people around for whom the default 8GB heap is
insufficient, and who have increased it to tens of GBs without