Manual:$wgMemoryLimit/ja

詳細
The minimum amount of memory that MediaWiki "needs"; MediaWiki will try to raise PHP's memory limit if it's below this amount.

注記
A check in Setup.php gets run on every page view to make sure that PHP's memory limit is at least this amount. If it's lower, MediaWiki will use ini_set to raise it if it can.

The installation script used to insert  in LocalSettings.php if the memory limit was below 20M. This led to problems when people raised the memory limit for their server later and found that it was mysteriously overridden.