Hi,
the loaned pages are explicitly wired down. Is it actually necessary
in all cases? It would probably be quite safe to not wire them, or
at least give an option to not have them wired.  Or would that open
a can of worms?

I note there is a comment in uvm/uvm_loan.c:
"""
 * each loan of a page to the kernel bumps the pg->wire_count.  the
 * kernel mappings for these pages will be read-only and wired.  since
 * the page will also be wired, it will not be a candidate for pageout,
 * and thus will never be pmap_page_protect()'d with VM_PROT_NONE.  a
 * write fault in the kernel to one of these pages will not cause
 * copy-on-write.  instead, the page fault is considered fatal.  this
 * is because the kernel mapping will have no way to look up the
 * object/anon which the page is owned by.  this is a good side-effect,
 * since a kernel write to a loaned page is an error.
"""

Jaromir
-- 
Jaromir Dolecek <Jaromir.Dolecek@ARTISYS.cz>
ARTISYS s.r.o., Stursova 71, 616 Brno, Czech Republic, phone: +420-5-41224836