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Subject: [OMPI devel] Memory hooks change testing
From: Brian Barrett (brbarret_at_[hidden])
Date: 2008-06-09 22:56:30

Hi all -

Per the RFC I sent out last week, I've implemented a revised behavior
of the memory hooks for high speed networks. It's a bit different
than the RFC proposed, but still very minor and fairly straight foward.

The default is to build ptmalloc2 support, but as an almost complete
standalone library. If the user wants to use ptmalloc2, he only has
to add -lopenmpi-malloc to his link line. Even when standalone and
openmpi-malloc is not linked in, we'll still intercept munmap as it's
needed for mallopt (below) and we've never had any trouble with that
part of ptmalloc2 (it's easy to intercept).

As a *CHANGE* in behavior, if leave_pinned support is turned on and
there's no ptmalloc2 support, we will automatically enable mallopt.
As a *CHANGE* in behavior, if the user disables mallopt or mallopt is
not available and leave pinned is requested, we'll abort. I think
these both make sense and are closest to expected behavior, but wanted
to point them out. It is possible for the user to disable mallopt and
enable leave_pinned, but that will *only* work if there is some other
mechanism for intercepting free (basically, it allows a way to ensure
your using ptmalloc2 instead of mallopt).

There is also a new memory component, mallopt, which only intercepts
munmap and exists only to allow users to enable mallopt while not
building the ptmalloc2 component at all. Previously, our mallopt
support was lacking in that it didn't cover the case where users
explicitly called munmap in their applications. Now, it does.

The changes are fairly small and can be seen/tested in the HG
repository bwb/mem-hooks, URL below. I think this would be a good
thing to push to 1.3, as it will solve an ongoing problem on Linux
(basically, users getting screwed by our ptmalloc2 implementation).


   Brian Barrett
   Open MPI developer