> Of course, Perl will never release any memory back to the O/S, but it will reuse it for its own purposes!

This is not correct. It depends on the implementation of the user-level malloc function. For more detail, see:

• Re: Not able to release memory (malloc implementation)

which notes that on Linux and Windows at least (unlike most other Perl platforms) the standard C Library malloc function does return "big" chunks of memory back to the OS.

Update: Though it's possible for a Perl built with a suitable malloc function to return memory to the OS, in practice this happens rarely, as described in ikegami's excellent Mini-Tutorial: Perl's Memory Management - which concludes with "You can't rely on memory being returned to the system, but it can happen ... if and when memory is returned to the OS is dependant on the memory allocation mechanism perl was compiled to use ... you are more likely to see memory being released to the OS on Windows".

See also:

• perlfaq3: How can I make my Perl program take less memory
• perlfaq3: How can I free an array or hash so my program shrinks

• Re: Re: Re: Clearing an Array of Array's from memory by Elian (whether the freed space is returned to the operating system is OS, OS version, C library, and allocation size dependent)
• Re^3: Memory usage double expected (run-time) (notes from Tim Bunce's excellent Profiling Memory Usage talk - with examples showing why Perl sometimes surprises by not returning memory to the OS)

• Is malloc part of the kernel or the C Library? (SO) - malloc is part of the standard C Library, not the OS kernel
• malloc_trim (Linux glibc-specific function to force malloc to free all eligible OS pages to the kernel)
• What causes Ruby memory bloat? (blog post describing malloc_trim)

References Added Later

• How to implement a Queue that doesn't leak memory? by anonymonk (2024)

Updated: minor improvements to wording; added extra references.

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