K 10
svn:author
V 4
jeff
K 8
svn:date
V 27
2019-09-10T19:08:01.578484Z
K 7
svn:log
V 391
Replace redundant code with a few new vm_page_grab facilities:
 - VM_ALLOC_NOCREAT will grab without creating a page.
 - vm_page_grab_valid() will grab and page in if necessary.
 - vm_page_busy_acquire() automates some busy acquire loops.

Discussed with:	alc, kib, markj
Tested by:	pho (part of larger branch)
Sponsored by:	Netflix
Differential Revision:	https://reviews.freebsd.org/D21546

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