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Re: [Haskell-cafe] ghc leaking memory?

Subject: Re: [Haskell-cafe] ghc leaking memory?
From: Simon Marlow
Date: Mon, 08 Mar 2010 11:07:30 +0000
On 06/03/2010 18:43, Antoine Latter wrote:
Including ghc-users.

On Sat, Mar 6, 2010 at 11:57 AM, Joachim Breitner<nomeata@xxxxxxxxxx>  wrote:
Hi,

in Debian, we are having some problems building large libraries (such as
agda, highlighting-kate, xmonad-contrib) on weaker architectures (sparc,
armel, s390) which compile with -fvia-C, especially when building the
profiling libraries.

In the case of highlighting-kate, there were really issues with the
code: A huge list of words which ghc seemed to try to inline caused it
consuming a lot of memory.

But in the case of agda, it even fails with relatively small modules:
https://buildd.debian.org/fetch.cgi?pkg=agda&arch=sparc&ver=2.2.6-3&stamp=1267334936&file=log&as=raw

Now, looking at the memory gauge on my computer while compiling such a
program with Cabal (which compiles all modules in one ghc call), it
looks like it is steadily increasing. Iâd expect ghc to free a lot of
memory when it is done with a module, but this does not seem to be the
case.

Is this a bug (i.e. memory leak) in ghc or expected behavior?

Can you verify that it is GHC leaking memory, and not gcc? I recommend turning off -fvia-C in particular unless you're sure that you need it.

It is expected that a --make compilation grows in memory over time, since the compiler accumulates information about modules that it has loaded. Having said that, it should not be retaining the entire compiled code of each module, only its interface. It might be hard to tell - in any case if you have an example where --make appears to be retaining too much memory then you should submit it as a bug.

Is there a way to make Cabal build each module on its own?

not at the moment, sorry.

>> Are there any fixes or work-arounds?

You can try using GC settings, e.g. +RTS -M<size>. It might be a good idea to set this using an environment variable, e.g. GHCRTS=-M<size> where <size> is roughly equal to the amount of real memory on your machine.

Cheers,
        Simon
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