How to limit Apache sub-process memory usage?

poige asked:

— Yeah, just that simple question. It’s too easy to consume a lot of RAM in brain-dead mod_XxX (say, mod_php) application, so I’m just wondering what does Apache allow to do as countermeasure.

My answer:

Apache doesn’t, but PHP does allow limiting the maximum amount of memory used, in php.ini. For instance:

memory_limit = 128M

Of course if someone hits this limit the actual amount of RAM used will be slightly higher due to PHP being embedded into Apache.

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