Clearing a page table entry's accessed bit (PG_A) and setting the

page's PG_REFERENCED flag in pmap_protect() can't really be justified.
In contrast to pmap_remove() or pmap_remove_all(), the mapping is not
being destroyed, so the notion that the page was accessed is not lost.
Moreover, clearing the page table entry's accessed bit and setting the
page's PG_REFERENCED flag can throw off the page daemon's activity
count calculation.  Finally, in my tests, I found that 15% of the
atomic memory operations being performed by pmap_protect() were only
to clear PG_A, and not change protection.  This could, by itself, be
fixed, but I don't see the point given the above argument.

Remove a comment from pmap_protect_pde() that is no longer meaningful
after the above change.

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