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From: Brian Barrett (brbarret_at_[hidden])
Date: 2005-12-06 11:07:44

On Dec 6, 2005, at 10:53 AM, Gleb Natapov wrote:

> On Tue, Dec 06, 2005 at 08:33:32AM -0700, Tim S. Woodall wrote:
>>> Also memfree hooks decrease cache efficiency, the better solution
>>> would
>>> be to catch brk() system calls and remove memory from cache only
>>> then,
>>> but there is no way to do it for now.
>> We are look at other options, including catching brk/munmap system
>> calls, and
>> will be experimenting w/ these on the trunk.
> This will be really interesting. How are you going to catch brk/munmap
> without kernel help? Last time I checked preload tricks don't work if
> syscall is done from inside libc itself.

All of the tricks we are looking at assume that nothing in libc calls
munmap. We can successfully catch free() calls from inside libc
without any problems. The LAM/MPI team and Myricom (with MPICH-gm)
have been doing this for many years without any problems. On the
small percentage of MPI applications that require some linker tricks
(some of the commercial apps are this way), we won't be able to
intercept any free/munmap calls, so we're going to fall back to our
RDMA pipeline algorithm.


   Brian Barrett
   Open MPI developer