--- a/runtime/doc/message.txt
+++ b/runtime/doc/message.txt
@@ -1,4 +1,4 @@
-*message.txt*   For Vim version 7.3c.  Last change: 2010 Jul 20
+*message.txt*   For Vim version 7.3c.  Last change: 2010 Jul 26
 
 
 		  VIM REFERENCE MANUAL    by Bram Moolenaar
@@ -467,7 +467,16 @@ Oh, oh.  You must have been doing someth
 is consuming your memory.  Be careful!  Vim is not completely prepared for an
 out-of-memory situation.  First make sure that any changes are saved.  Then
 try to solve the memory shortage.  To stay on the safe side, exit Vim and
-start again.  Also see |msdos-limitations|.
+start again.
+
+Buffers are only partly kept in memory, thus editing a very large file is
+unlikely to cause an out-of-memory situation.  Undo information is completely
+in memory, you can reduce that with these options:
+- 'undolevels'  Set to a low value, or to -1 to disable undo completely.  This
+  helps for a change that affects all lines.
+- 'undoreload' Set to zero to disable.
+
+Also see |msdos-limitations|.
 
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