On Wed, 10 Aug 2011 11:47:19 +0100
Mel Gorman [off-list ref] wrote:

The percentage that must be in writeback depends on the priority. At
default priority, all of them must be dirty. At DEF_PRIORITY-1, 50%
of them must be, DEF_PRIORITY-2, 25% etc. i.e. as pressure increases
the greater the likelihood the process will get throttled to allow
the flusher threads to make some progress.

It'd be nice if the code comment were to capture this piece of implicit
arithmetic.  After all, it's a magic number and magic numbers should
stick out like sore thumbs.

And.. how do we know that the chosen magic numbers were optimal?

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