Jeff Muizelaar [:jrmuizel] Reporter
	Description • 9 years ago

When playing around with the minimap on http://people.mozilla.org/~jmuizelaar/test-cases/wide-page/planet.freedesktop.org.html I see us expanding the display port in a direction opposite of the direction we're scrolling. This causes us to spend time painting content that will not be shown and fall further behind.

	Kartikaya Gupta (email:kats@mozilla.staktrace.com)
	Comment 1 • 9 years ago

Well there's really two separate effects happening - one is that we expand the displayport, and the second is that we shift the displayport in the direction of scrolling. If the shift isn't big enough relative to the expansion it will appear that the displayport is growing in the wrong direction.

As it turns out, on desktop our skate and stationary displayport multipliers are both 3.5 so the displayport enlargement is likely coming from the high-memory adjustment that Mason added recently in bug 1208636. We should further update the code to shift the displayport in the direction of scrolling by a larger amount if this high-memory adjustment is kicking in.

	Kartikaya Gupta (email:kats@mozilla.staktrace.com)
	Comment 2 • 9 years ago

Also, Jeff, if you're seeing jank at the point that the displayport changes size, try setting the apz.x_skate_highmem_adjust and apz.y_skate_highmem_adjust prefs to 0 and see if that fixes it.

It may be that we don't want the highmem adjustment at all, because as BenWa pointed out to me on IRC, having more memory doesn't mean we have a higher memory bandwidth or more CPU and those could bottleneck paint/transaction time as well.

	Jeff Muizelaar [:jrmuizel] Reporter
	Comment 3 • 9 years ago

I think it's better without the highmem. It would be nice to show it with numbers though.

	Kartikaya Gupta (email:kats@mozilla.staktrace.com)
	Comment 4 • 8 years ago

We already turned off the highmem adjustment, so I think there's nothing left to do here.