Having tweaked mod_perl with some preloading and other things a pmap on solaris shows our apache processes using 4-5Mb of private memory (mainly heap), the full process size is around 20Mb.
The proprietry module we currently have has process sizes of around 16Mb, but their private data section on pmap is around 200-300k.
I know perl is somewhat more memory intensive, however I remain convinced that each of our modules is not using 4-5 Mb of real memory (7Mb before I started preloading modules), and that actually most of the heap is still actually "copy-on-write" and the perl processes are merely sharing their code on the heap, however I have no idea how to actually get a dump of the memory status of a process and tell which segments of it are still "copy-on-write".
If anyone can give me any pointers how I might track all this info down, or alternatively any good ways of reducing the memory usage any further, I would be very grateful. The issue arises because we need to run up to 800 apache process on each of our frontend webservers at peak times (mainly to deal with slow connections), which would probably require (at 1-2Gb real memory per CPU) 16-32Gb swap space. Our sysadmin is understandably a little nervous about this.
One other issue I had was that I can preload all of the modules in startup.pl, however each module still retains the extra memory unless I actually remove the uses/requires from the module which is using it. This is fine but since we are using objects in perl this causes an error (unless I'm missing something obvious, which is possibly the case).
Thanks Gareth
** Yes the obvious solution to this is to go with threaded, however thats the "next step" and requires some more work on making our "other" apache modules reentrant. I'm pretty sure making our perl code threadsafe is fairly easy, however we have several other apache modules we've converted to apache2, but are still written in C.
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