svn commit: r287121 - head/sys/vm

[Alan Cox]

Author: alc
Date: Tue Aug 25 01:01:25 2015
New Revision: 287121
URL: https://svnweb.freebsd.org/changeset/base/287121

Log:
  Testing whether a page is dirty does not require the page lock.  Moreover,
  it may involve a pmap operation that iterates over the page's PV list, so
  unnecessarily holding the page lock is undesirable.
  
  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	Mon Aug 24 23:40:36 2015	(r287120)
+++ head/sys/vm/vm_pageout.c	Tue Aug 25 01:01:25 2015	(r287121)
@@ -415,10 +415,13 @@ more:
 			ib = 0;
 			break;
 		}
-		vm_page_lock(p);
 		vm_page_test_dirty(p);
-		if (p->dirty == 0 ||
-		    p->queue != PQ_INACTIVE ||
+		if (p->dirty == 0) {
+			ib = 0;
+			break;
+		}
+		vm_page_lock(p);
+		if (p->queue != PQ_INACTIVE ||
 		    p->hold_count != 0) {	/* may be undergoing I/O */
 			vm_page_unlock(p);
 			ib = 0;
@@ -442,10 +445,11 @@ more:
 
 		if ((p = vm_page_next(ps)) == NULL || vm_page_busied(p))
 			break;
-		vm_page_lock(p);
 		vm_page_test_dirty(p);
-		if (p->dirty == 0 ||
-		    p->queue != PQ_INACTIVE ||
+		if (p->dirty == 0)
+			break;
+		vm_page_lock(p);
+		if (p->queue != PQ_INACTIVE ||
 		    p->hold_count != 0) {	/* may be undergoing I/O */
 			vm_page_unlock(p);
 			break;