nginx+php-fpm randomly goes down

Hello!

I have been using nginx + php-fpm for a while now, mostly on small personal projects. But a few weeks ago I started using nginx for one of my bigger sites (10-20k pageviews daily). All my settings are pretty much default.

Here is what happens:
After running for 2-3 days it starts showing 404 error on everything. Only way to fix this is to reboot the server, and then it works again.

Do anyone know what's wrong?

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My default file: http://pastebin.com/0pc5HZpr