Introduce a kconfig option READAHEAD_ALLOW_OVERHEADS to enable users
to choose extra features that have overheads.

Features with overheads will be disabled by default.

Signed-off-by: Wu Fengguang <wfg@mail.ustc.edu.cn>
---

--- linux-2.6.17-mm2.orig/mm/Kconfig
+++ linux-2.6.17-mm2/mm/Kconfig
@@ -182,10 +182,15 @@ config ADAPTIVE_READAHEAD
 	  It is known to work well for many desktops, file servers and
 	  postgresql databases. Say Y to try it out for yourself.
 
+config READAHEAD_ALLOW_OVERHEADS
+	bool "Allow extra features with overheads"
+	default n
+	depends on ADAPTIVE_READAHEAD
+
 config DEBUG_READAHEAD
 	bool "Readahead debug and accounting"
 	default y
-	depends on ADAPTIVE_READAHEAD
+	depends on READAHEAD_ALLOW_OVERHEADS
 	select DEBUG_FS
 	help
 	  This option injects extra code to dump detailed debug traces and do

--