MAP_POPULATE supports both file and anonymous mappings.

Since 2.6.23, MAP_POPULATE supports private mappings.
Since 2.6.23, MAP_NONBLOCK causes MAP_POPULATE to be a no-op.

man2/mmap.2

@@ -36,7 +36,7 @@
 .\" Modified 2006-12-04, mtk, various parts rewritten
 .\" 2007-07-10, mtk, Added an example program.
 .\"
-.TH MMAP 2 2008-04-22 "Linux" "Linux Programmer's Manual"
+.TH MMAP 2 2008-05-05 "Linux" "Linux Programmer's Manual"
 .SH NAME
 mmap, munmap \- map or unmap files or devices into memory
 .SH SYNOPSIS
@@ -226,6 +226,15 @@ Only meaningful in conjunction with
 Don't perform read-ahead:
 only create page tables entries for pages
 that are already present in RAM.
+Since Linux 2.6.23,
+this flags causes
+.BR MAP_POPULATE
+to do nothing.
+One day the combination of
+.BR MAP_POPULATE
+and
+.BR MAP_NONBLOCK
+may be re-implemented.
 .TP
 .B MAP_NORESERVE
 Do not reserve swap space for this mapping.
@@ -243,9 +252,11 @@ In kernels before 2.6, this flag only had effect for
 private writable mappings.
 .TP
 .BR MAP_POPULATE " (since Linux 2.5.46)"
-Populate (prefault) page tables for a file mapping,
-by performing read-ahead on the file.
+Populate (prefault) page tables for a mapping.
+For a file mapping, this causes read-ahead on the file.
 Later accesses to the mapping will not be blocked by page faults.
+.BR MAP_POPULATE
+is only supported for private mappings since Linux 2.6.23.
 .LP
 Of the above flags, only
 .B MAP_FIXED