If a hidden page has never been visible, no need to gently ramp into throttling - treat it the same as a page that has been viewed, but has been in the background for a long time. Why? The throttling mechanism scales with the amount of background work by shifting the limit - once all background pages have maxed out the limit, they should no longer be burden of the system. However the mechanism doesn't currently do anything to accelerate towards the limit based on the number of pages in the ramp up phase, and ramp up duration is proportional to limit (so ramping up to a high limit takes a long time). So if you quickly create a large number of hidden pages the system may be under excessive load for a while, as we slowly ramp up to a limit that will adequately constrain resource consumption. In cases where a large number of hidden pages are rapidly generated, many likely remain in the pre-render state, so this mitigation should typically help.
Created attachment 273034 [details] Fix
Comment on attachment 273034 [details] Fix r=me
Transmitting file data .. Committed revision 197588.