I attempted to upload a 250MB file by dragging it into a ticket comment field. The upload progressed normally, but after it hit 100%, I got a popup in the lower left with a nasty 502 Bad Gateway error. I can see from system logs that phabricator allocated a lot of memory suddenly, possibly consuming as much as 2GB (it happened so suddenly that I don't have any metrics data).
We have phabricator running on an EC2 c4.xlarge which has 7.5GB of memory. About 2GB of memory is available (cache + free).
For reference, our max file upload size setting is 512MB.