Before anyone posts something about checking php.ini, bear in mind there are all sorts of ways it could be overridden. Where's the admin page or panel that lists the amount of RAM available to mediawiki?
(Due diligence: Searches turned up nothing. Proof in links below)
https://www.google.com/search?q=mediawiki+admin+panel&ie=utf-8&oe=utf-8&client=firefox-b-1 only relevant link is https://www.mediawiki.org/wiki/Manual:System_administration which contains nothing about memory or RAM
https://www.google.com/search?q=mediawiki+admin+UI+how+much+memory+is+allocated&ie=utf-8&oe=utf-8&client=firefox-b-1 again nothing
https://www.google.com/search?q=mediawiki+how+to+check+how+much+memory+is+allocated&ie=utf-8&oe=utf-8&client=firefox-b-1 again, nothing. First link suggests increasing amount of RAM but that isn't useful if my php.ini is being ignored for unknown reasons