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Coping with, and minimizing, memory usage in Common Lisp (SBCL)

Asked 2009-04-02T08:52:16.397
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I have a VPS with not very much memory (256Mb) which I am trying to use for Common Lisp development with SBCL+Hunchentoot to write some simple web-apps. A large amount of memory appears to be getting used without doing anything particularly complex, and after a while of serving pages it runs out of memory and either goes crazy using all swap or (if there is no swap) just dies.

So I need help to:

  • Find out what is using all the memory (if it's libraries or me, especially)
  • Limit the amount of memory which SBCL is allowed to use, to avoid massive quantities of swapping
  • Handle things cleanly when memory runs out, rather than crashing (since it's a web-app I want it to carry on and try to clean up).

I assume the first two are reasonably straightforward, but is the third even possible? How do people handle out-of-memory or constrained memory conditions in Lisp?

(Also, I note that a 64-bit SBCL appears to use literally twice as much memory as 32-bit. Is this expected? I can run a 32-bit version if it will save a lot of memory)

memory lisp common-lisp out-of-memory sbcl
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I would not be surprised by a 64-bit SBCL using twice the meory, as it will probably use a 64-bit cell rather than a 32-bit one, but couldn't say for sure without actually checking.

Typical things that keep memory hanging around for longer than expected are no-longer-useful references that still have a path to the root allocation set (hash tables are, I find, a good way of letting these things linger). You could try interspersing explicit calls to GC in your code and make sure to (as far as possible) not store things in global variables.

answered 2009-04-02T09:47:17.217

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