issue with direct reclaims and kswapd reclaims on 2.6.35.7

[Jeffrey Vanhoof <jdv1029@gmail.com>]

On a 2.6.35.7 based kernel, on a portable device with 512MB RAM, I am
seeing the following issues while consuming 20Mbps video content:
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.
3) kswapd not reclaiming pages quickly enough due to falling into
congestion_wait() very often.
4) power consumption is degraded as a result of time being spent in
io_schedule_timeout() called within congestion_wait(). (the power
c-state will stay in C0)

Are there specific patches which can be easily back-ported to K35
which may address most of these issues?

For file read performance, I believe it is better for kswapd to
reclaim memory instead of hitting a direct reclaim, and for power it
would be best that while reclaiming memory in kswapd that
io_schedule()/io_schedule_timeout() is never called unless absolutely
required.

Are any of the workarounds listed below appropriate to use?
1) change the congestion_wait() timeout value in balance_pgdat() from
HZ/10 to HZ/50. This allows for faster reclaims in kswapd and limits
the time spend in congestion_wait().
2) change SWAP_CLUSTER_MAX from 32 to 128 or higher (swap is enabled,
but there is no swap).
3) change DEF_PRIORITY from 12 to 9. This results in a larger scan and
pages are reclaimed quicker. Also, this causes congestion_wait() to be
called less frequently due to the likelyhood of pages being found with
increase priority.

Any help would be appreciated.

Thanks,
Jeff V.

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