The following can be read in the Samba cvs.log,
it makes me believe that shmem is faster than mmap.
Informix also uses shmem and not mmap.

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Date:   Wednesday October 29, 1997 @ 1:19
Author: tridge

Update of /data/cvs/samba/source
In directory samba:/tmp/cvs-serv8959

Modified Files:
        Makefile includes.h locking_shm.c proto.h shmem.c smb.h
Added Files:
        shmem_sysv.c
Log Message:
SYSV IPC implementation of fast share modes.

It will try sysv IPC first, then if that fails it will try mmap(),
then after that it will try share files.

I have defined USE_SYSV_IPC for Linux, Solaris and HPUX at the
moment. Probably a lot more could have it defined. In fact, the vast
majority of systems support it. Need autoconf again :-)

It should actually be faster than the mmap() version, and doesn't need
any lock files. This means the problem of the share mem file being on
a NFS drive will be gone.
****************************************************************************
***

Andreas

Thu, 23 Apr 1998 19:18:06 +0200
Zeugswetter Andreas SARZ <Andreas.Zeugswetter@telecom.at>
Using mmap instead of shmem