Live Visitors widget Memory exchausting

I’ve been running Piwik for a while, but suddenly I get this in my Live Visitors widget;
Fatal error: Allowed memory size of 536870912 bytes exhausted (tried to allocate 72 bytes) in /var/www/html/core/DataTable/Renderer/Php.php on line 148

memory_limit is set to 512MB, the server currently has 7,7GB of free memory, the mysql database is roughly 140MB and we’re having about 6000 visitors a day. Has anyone seen this or encountered it? Or even better, know about a fix?

Let me know if anything else is needed to go deeper into the problem.

Hmm, seems like i fixed it by increasing memory_limit further, to a total of 1024MB. I’ll keep an eye on the feature to see if it ever needs more.