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Subject: Re: [OMPI devel] RFC: make mpi_leave_pinned=1 the default
From: Patrick Geoffray (patrick_at_[hidden])
Date: 2008-07-06 13:28:32


Jeff Squyres wrote:
> WHAT: make mpi_leave_pinned=1 by default when a BTL is used that would
> benefit from it (when possible; 0 when not, obviously)

> Comments?

The probable reason registration cache (aka leave_pinned) is disabled by
default is that it may be unsafe. Even if you use mallocopt to never
return memory to the OS, how do you guarantee that:
* malloc always enforce the mallocopt *hints*.
* pinned memory can safely be fork()ed (system() for example).
* pinned memory can safely be unmmap()ed (Direct I/O or file mapping for
example).

If you can't, one solution may be to write a simple MPI code that
corrupts MVAPICH and make some noise about it.

My 2 cents.

Patrick