[m-dev.] boehm gc USE_MUNMAP

Peter Wang novalazy at gmail.com
Fri Jan 18 16:50:03 AEDT 2008

On 2008-01-18, Julien Fischer <juliensf at csse.unimelb.edu.au> wrote:
>  On Fri, 18 Jan 2008, Peter Wang wrote:
> > We're seeing (probably) heap fragmentation leading to unexpectedly large
> > heaps for a particular application.  Following the Boehm GC
> > documentation, I linked it against a copy of libgc built with the
> > USE_MUNMAP option which lets it return unused pages to the OS.
> > It solved the problem with that application.
> >
> > The following speed test on saturn shows a ~20% slow down with this
> > option, so I assume we wouldn't want it on by default.  However, we
> > could add it as a new grade component, say gc_unmap.  I think it would
> > be generally useful.
>  I'm not exactly thrilled about the prospect of adding yet-another-grade,
>  but since these things are easier to use when you can install two
>  versions of the library concurrently, e.g. asm_fast.gc and
>  asm_fast.gc_unmap, I don't have any objections to adding an new
>  grade component.

I'm not thrilled at updating the scripts to support another gc grade
either.  As it only changes which gc library an application links
against, it would be a real waste to install asm_fast.gc and
asm_fast.gc_unmap -- all the files would be exactly the same.

Maybe the use of libgc_unmap should just be an option passed to mmc or
ml?  I don't know how the install process would work though.


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