MFC r265418

  Prior to r254304, a separate function, vm_pageout_page_stats(), was used
  to periodically update the reference status of the active pages.  This
  function was called, instead of vm_pageout_scan(), when memory was not
  scarce.  The objective was to provide up to date reference status for
  active pages in case memory did become scarce and active pages needed to
  be deactivated.

  The active page queue scan performed by vm_pageout_page_stats() was
  virtually identical to that performed by vm_pageout_scan(), and so r254304
  eliminated vm_pageout_page_stats().  Instead, vm_pageout_scan() is
  called with the parameter "pass" set to zero.  The intention was that when
  pass is zero, vm_pageout_scan() would only scan the active queue.
  However, the variable page_shortage can still be greater than zero when
  memory is not scarce and vm_pageout_scan() is called with pass equal to
  zero.  Consequently, the inactive queue may be scanned and dirty pages
  laundered even though that was not intended by r254304.  This revision
  fixes that.

1 files changed, 5 insertions, 3 deletions

diff --git a/sys/vm/vm_pageout.c b/sys/vm/vm_pageout.c
index d2ccfa0..9ccb606 100644
--- a/sys/vm/vm_pageout.c
+++ b/sys/vm/vm_pageout.c
@@ -942,13 +942,15 @@ vm_pageout_scan(struct vm_domain *vmd, int pass)
 	 */
 	addl_page_shortage = 0;
 
-	deficit = atomic_readandclear_int(&vm_pageout_deficit);
-
 	/*
 	 * Calculate the number of pages we want to either free or move
 	 * to the cache.
 	 */
-	page_shortage = vm_paging_target() + deficit;
+	if (pass > 0) {
+		deficit = atomic_readandclear_int(&vm_pageout_deficit);
+		page_shortage = vm_paging_target() + deficit;
+	} else
+		page_shortage = deficit = 0;
 
 	/*
 	 * maxlaunder limits the number of dirty pages we flush per scan.