It appears that newly cached entries have their body files remain in dirty "mapped file" VM entries until the file is closed.
With a little msync() magic we can turn this dirty memory clean.
Created attachment 261747 [details]
Comment on attachment 261747 [details]
Clearing flags on attachment: 261747
Committed r190121: <http://trac.webkit.org/changeset/190121>
All reviewed patches have been landed. Closing bug.