svn commit: r310358 - stable/11/sys/vm

[Konstantin Belousov]

Author: kib
Date: Wed Dec 21 09:18:53 2016
New Revision: 310358
URL: https://svnweb.freebsd.org/changeset/base/310358

Log:
  MFC r310098:
  Provide introductory description of the default pager.

Modified:
  stable/11/sys/vm/default_pager.c
Directory Properties:
  stable/11/   (props changed)

Modified: stable/11/sys/vm/default_pager.c
==============================================================================
--- stable/11/sys/vm/default_pager.c	Wed Dec 21 09:15:25 2016	(r310357)
+++ stable/11/sys/vm/default_pager.c	Wed Dec 21 09:18:53 2016	(r310358)
@@ -63,6 +63,16 @@ static boolean_t default_pager_haspage(v
 		int *);
 /*
  * pagerops for OBJT_DEFAULT - "default pager".
+ *
+ * This pager handles anonymous (no handle) swap-backed memory, just
+ * like the swap pager.  It allows several optimizations based on the
+ * fact that no pages of a default object can be swapped out.  The
+ * most important optimization is in vm_fault(), where the pager is
+ * never asked for a non-resident page.  Instead, a freshly allocated
+ * zeroed page is used.
+ *
+ * On the first request to page out a page from a default object, the
+ * object is converted to swap pager type.
  */
 struct pagerops defaultpagerops = {
 	.pgo_alloc =	default_pager_alloc,