MFC r215471:

MFC r215471:
In vm_object_page_clean(), handle the pages that might be cached
or not written by vm_pageout_flush().

MFC r215574:
The runlen returned from vm_pageout_flush() might be zero legitimately

MCF r215610:
Eliminate the mab, maf arrays and related variables.
The change also fixes off-by-one error in the calculation of mreq.

MFC r215796:
After the sleep caused by encountering a busy page, relookup the page.

git-svn-id: svn://svn.freebsd.org/base/stable/8@215866 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f