Understanding the -A and the -H flags

[Johan Tibell]

Hi!

I'm trying to understand the interaction between the -A and -H RTS
flags. The documentation at

  http://www.haskell.org/ghc/docs/7.4.1/html/users_guide/runtime-control.html

says that if you use -H (with or without an argument) it implicitly
implies some value of -A. However, it's not clear to me what value -A
will get and how that value is related to the value of -H. For
example, if I set the suggested heap size to 1G, using -H1G, surely
the size of the nursery (-A) won't be "whatever is left over," but
something more reasonable e.g. the size of the L2 cache?

Perhaps it would make sense to document the actual algorithm used to
set -A given -H (with and without argument.)

Cheers,
Johan