Actually, loading a module before fork will more likely save you memory. Forking uses a "copy on write" semantic. That is, the child process shares its memory pages with its parents until one or the other tries to write into that page. Only at that point does it make a copy of that page for the process that is trying to write.

So if you take an application that has a fairly large number of modules (and the perl interpretter itself) sitting in pages that aren't going to get overwritten, compared to a fairly small number of pages that are getting actively written to, then preloading is going to save you memory (if a fair portion of the modules will be used in more than one of the forked processes). Not to mention the fact that it will also save you time.

Anyway, here's an example. I've got a web server here with three processes: one is a controller process, and two are worker processes. In the first example, I preload a large number of the perl modules before forking. In the second example, the modules are loaded after forking. 

  PID USER     PRI  NI  SIZE  RSS SHARE STAT  LIB %CPU %MEM   TIME COMMAND
16701 me         0   0 35712  34M 31832 S       0  0.0  1.6   0:02 httpd
18302 me         0   0 41400  40M 33100 S       0  0.0  1.8   0:04 httpd
32301 me         0   0 41932  40M 33776 S       0  0.0  1.9   0:02 httpd


  PID USER     PRI  NI  SIZE  RSS SHARE STAT  LIB %CPU %MEM   TIME COMMAND
 2906 me         0   0  4608 4608  3052 S       0  0.0  0.2   0:00 httpd
 2907 me         0   0 35084  34M  5844 S       0  0.0  1.5   0:10 httpd
 2908 me         0   0 38804  37M  5880 S       0  0.0  1.7   0:11 httpd
Paying careful attention to the SHARE column, you see that the total actual used memory is about 50 megs for the preloading and about 65 megs for the non-preloading. Also, you see that two seconds of processing time in the controller (parent) process when preloading that aren't in the controller process when not preloading. You can think of those two seconds as "shared" seconds, too, in much the same way as the shared memory (because two seconds happens to be about how long it takes to load the large corpus of perl modules involved here). 
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In reply to Re: Re: latest on ithreads vs forks? by etcshadow
in thread latest on ithreads vs forks? by Anonymous Monk

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