Huge space leak of GHC API 7.8.x?

14 Jul 2014

      Hi,

Some guys reported to me that ghc-mod uses about 1G bytes on Mac and I
can reproduce this. I tried to understand why ghc-mod uses such huge
memory.

I found that GHC API 7.8.x uses much more memory than GHC API 7.6.x.
Attached two files demonstrate this:

	- A.hs -- Simple program using GHC API (copied from Wiki)
	- B.hs -- A target file, just hello world

You can compile A.hs as follows:

	% ghc A.hs -package ghc -package ghc-paths

The following is the result:

            Mac (64bit)  Linux (64bit)
GHC 7.6.3:         20MB            4MB
GHC 7.8.3:        106MB           13MB

So, I think GHC API 7.8.x has huge space leak. (And I'm wondering why
Mac uses much more memory than Linux).

I would like to hear opinions from you guys.

--Kazu

<A.hs>
import Control.Concurrent
import CoreMonad (liftIO)
import DynFlags
import GHC
import GHC.Paths (libdir)

main = defaultErrorHandler defaultFatalMessager defaultFlushOut $ do
    runGhc (Just libdir) $ do
        dflags <- getSessionDynFlags
        let dflags' = dflags {hscTarget = HscInterpreted
                             ,ghcLink   = LinkInMemory
                             ,ghcMode   = CompManager
                             }
        setSessionDynFlags dflags'
        target <- guessTarget "B.hs" Nothing
        setTargets [target]
        load LoadAllTargets
        liftIO $ threadDelay 10000000
</A.hs>
<B.hs>
module B where

main = print "Hello, World!"
</B.hs>

Huge space leak of GHC API 7.8.x?

Kazu Yamamoto