Setting PG_REFERENCED on the requested page in swap_pager_getpages() is either redundant or harmful, depending on the caller.  For example, when called by vm_fault(), it is redundant.  However, when called by vm_thread_swapin(), it is harmful.  Specifically, if the thread is later swapped out, having PG_REFERENCED set on its stack pages leads the page daemon to reactivate these stack pages and delay their reclamation.
Setting PG_REFERENCED on the requested page in swap_pager_getpages() is
either redundant or harmful, depending on the caller.  For example, when
called by vm_fault(), it is redundant.  However, when called by
vm_thread_swapin(), it is harmful.  Specifically, if the thread is later
swapped out, having PG_REFERENCED set on its stack pages leads the page
daemon to reactivate these stack pages and delay their reclamation.

Reviewed by:	kib
MFC after:	3 weeks

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