svn commit: r238359 - head/sys/vm

[Attilio Rao]

Author: attilio
Date: Wed Jul 11 01:04:59 2012
New Revision: 238359
URL: http://svn.freebsd.org/changeset/base/238359

Log:
  Document the object type movements, related to swp_pager_copy(),
  in vm_object_collapse() and vm_object_split().
  
  In collabouration with:	alc
  MFC after:	3 days

Modified:
  head/sys/vm/vm_object.c

Modified: head/sys/vm/vm_object.c
==============================================================================
--- head/sys/vm/vm_object.c	Tue Jul 10 23:11:52 2012	(r238358)
+++ head/sys/vm/vm_object.c	Wed Jul 11 01:04:59 2012	(r238359)
@@ -1381,6 +1381,12 @@ retry:
 
 		/*
 		 * Transfer any cached pages from orig_object to new_object.
+		 * If swap_pager_copy() found swapped out pages within the
+		 * specified range of orig_object, then it changed
+		 * new_object's type to OBJT_SWAP when it transferred those
+		 * pages to new_object.  Otherwise, new_object's type
+		 * should still be OBJT_DEFAULT and orig_object should not
+		 * contain any cached pages within the specified range.
 		 */
 		if (__predict_false(orig_object->cache != NULL))
 			vm_page_cache_transfer(orig_object, offidxstart,
@@ -1719,6 +1725,9 @@ vm_object_collapse(vm_object_t object)
 				 * swap_pager_copy() can sleep, in which case
 				 * the backing_object's and object's locks are
 				 * released and reacquired.
+				 * Since swap_pager_copy() is being asked to
+				 * destroy the source, it will change the
+				 * backing_object's type to OBJT_DEFAULT.
 				 */
 				swap_pager_copy(
 				    backing_object,