w.r.t:
> 1) direct reclaims occurring quite frequently, resulting in delayed
> file read requests
> 2) direct reclaims falling into congestion_wait() even though no
> congestion at the time, this results in video jitter.

Backporting the following changes seemed to greatly improve these issues:
-vmscan: synchronous lumpy reclaim should not call congestion_wait()
-writeback: do not sleep on the congestion queue if there are no
congested BDIs or if significant congestion is not being encountered
in the current zone
-vmscan: avoid setting zone congested if no page dirty

w.r.t.:
> 3) kswapd not reclaiming pages quickly enough due to falling into
> congestion_wait() very often. (or stays in congestion_wait() for too long)

The attached patch takes an idea from Mel Gorman's patch for
"writeback: do not sleep on the congestion queue if there are no
congested BDIs or if significant congestion is not being encountered
in the current zone" and applies it around the congestion_wait() in
balance_pgdat(). The idea is that if there is no congestion then avoid
potentially wait for too long. Comments or alternate solutions would
be appreciated.

Thanks,
Jeff Vanhoof