svn commit: r350021 - head/sys/i386/i386

[Alan Cox]

Author: alc
Date: Tue Jul 16 03:09:03 2019
New Revision: 350021
URL: https://svnweb.freebsd.org/changeset/base/350021

Log:
  Revert r349973.  Upon further reflection, I realized that the comment
  deleted by r349973 is still valid on i386.  Restore it.
  
  Discussed with:	   markj

Modified:
  head/sys/i386/i386/pmap.c

Modified: head/sys/i386/i386/pmap.c
==============================================================================
--- head/sys/i386/i386/pmap.c	Mon Jul 15 23:43:38 2019	(r350020)
+++ head/sys/i386/i386/pmap.c	Tue Jul 16 03:09:03 2019	(r350021)
@@ -5096,6 +5096,13 @@ __CONCAT(PMTYPE, ts_referenced)(vm_page_t m)
 			 * reference bit will result in clearing that bit.
 			 * This function is designed to avoid the selection of
 			 * the same 4KB page for every 2- or 4MB page mapping.
+			 *
+			 * On demotion, a mapping that hasn't been referenced
+			 * is simply destroyed.  To avoid the possibility of a
+			 * subsequent page fault on a demoted wired mapping,
+			 * always leave its reference bit set.  Moreover,
+			 * since the superpage is wired, the current state of
+			 * its reference bit won't affect page replacement.
 			 */
 			if ((((pa >> PAGE_SHIFT) ^ (pv->pv_va >> PDRSHIFT) ^
 			    (uintptr_t)pmap) & (NPTEPG - 1)) == 0 &&