[PATCH 6/7] mm: vmscan: Throttle reclaim if encountering too many dirty pages under writeback

[Andrew Morton]

On Wed, 10 Aug 2011 11:47:19 +0100
Mel Gorman <mgorman at suse.de> 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?