ghci leaks memory when loading a file
In the 6.12 series, ghci leaks memory when loading definitions. This appears to be a regression from previous releases. The problem appears in both 6.12.1 and 6.12.2, but not in 6.8.3 or 6.10.4.
As a test, take the attached Hello World file, fire up ghci, and :load Hello.hs. Watch the memory usage of ghci---each time you repeat the load command, the memory usage of the process grows. (It grows slowly on this simple example, but on a real project, the growth can be several megabytes per :load.)
I discovered this due to my workflow. When programming Haskell, I typically use emacs with haskell-mode, and frequently reload the definitions of the code I am working on. After upgrading to 6.12.1, after coding for some time, I noticed my 8GB machine was swapping. (It is faster to :reload the file rather than :load, and reloading doesn't appear to suffer from the memory leak, but sometimes I switch between modules and :reload is not applicable.)
My workaround for now is to regularly restart my ghci processes to prevent their memory usage from growing so much that my system starts swapping.
I have observed this bug on 32- and 64-bit GHCi on various versions of Ubuntu, on both Intel and AMD processors.