Re: [PATCH 7/8] writeback: sync old inodes first in background writeback

[Rik van Riel]

On 07/25/2010 11:08 PM, Wu Fengguang wrote:

> We do need some throttling under memory pressure. However stall time
> more than 1s is not acceptable. A simple congestion_wait() may be
> better, since it waits on _any_ IO completion (which will likely
> release a set of PG_reclaim pages) rather than one specific IO
> completion. This makes much smoother stall time.
> wait_on_page_writeback() shall really be the last resort.
> DEF_PRIORITY/3 means 1/16=6.25%, which is closer.

I agree with the max 1 second stall time, but 6.25% of
memory could be an awful lot of pages to scan on a system
with 1TB of memory :)

Not sure what the best approach is, just pointing out
that DEF_PRIORITY/3 may be too much for large systems...

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