svn commit: r265418 - head/sys/vm

[Alan Cox]

Author: alc
Date: Tue May  6 03:42:04 2014
New Revision: 265418
URL: http://svnweb.freebsd.org/changeset/base/265418

Log:
  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.
  
  Reported by:	avg
  MFC after:	1 week
  Sponsored by:	EMC / Isilon Storage Division

Modified:
  head/sys/vm/vm_pageout.c

Modified: head/sys/vm/vm_pageout.c
==============================================================================
--- head/sys/vm/vm_pageout.c	Tue May  6 03:38:04 2014	(r265417)
+++ head/sys/vm/vm_pageout.c	Tue May  6 03:42:04 2014	(r265418)
@@ -942,13 +942,15 @@ vm_pageout_scan(struct vm_domain *vmd, i
 	 */
 	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.