Linux and mm session handler -- does it really handle high load?

I have tried mm as a session handler three times, on three different Linux boxes. Each one was a server under heavy load, running many concurrent sessions, so I was hoping mm would solve some performance issues, but have been disappointed each time. So far, I am 0 for 3 on this, having done _everything_ by the book. I am running completely standard stuff: Apache (latest source), MySQL, PHP 4.0.6, or PHP 4.1.1. On two mature kernels ( 2.2.19, and 2.4.17), using either the RPM for mm, or compiling from source, I have come up against the same wall: Every time I try one of these heavy-load systems with the mm session handler, performance gets WORSE instead of better. On the latest system (Dual 1.1 GHz, 2 GB RAM, 4-disk RAID 0+1), I was losing sessions left and right. The system could only handle about 100-150 concurrent users before session keys started disappearing, and users would get logged out, On kernel 2.2.19, over a period of minutes, performance would deteriorate until I started getting segfaults. On each system, when I went back to "files" as a session handler, the problem went away. So, is there something I am doing wrong? Is there some trick to configuring mm and PHP, that is not documented, or is there a problem with Linux and mm itself? Has anyone here successfully used mm as a session handler? On a high-performance system? Any ideas, or should I submit this as a bug? If so, is it a bug with Linux, with the MM library, or with PHP? Thanks, Rick Morris