Linux 3.0: Shrinker compatibility

Update the the wrapper macros for the memory shrinker to handle
this 4th API change.  The callback function now takes a
shrink_control structure.  This is certainly a step in the
right direction but it's annoying to have to accomidate yet
another version of the API.

config/spl-build.m4

@@ -81,6 +81,7 @@ AC_DEFUN([SPL_AC_CONFIG_KERNEL], [
 	SPL_AC_SHRINK_ICACHE_MEMORY
 	SPL_AC_KERN_PATH_PARENT
 	SPL_AC_2ARGS_ZLIB_DEFLATE_WORKSPACESIZE
+	SPL_AC_SHRINK_CONTROL_STRUCT
 ])
 
 AC_DEFUN([SPL_AC_MODULE_SYMVERS], [
@@ -1810,3 +1811,25 @@ AC_DEFUN([SPL_AC_2ARGS_ZLIB_DEFLATE_WORKSPACESIZE],
 		AC_MSG_RESULT(no)
 	])
 ])
+
+dnl #
+dnl # 2.6.39 API change,
+dnl # Shrinker adjust to use common shrink_control structure.
+dnl #
+AC_DEFUN([SPL_AC_SHRINK_CONTROL_STRUCT], [
+	AC_MSG_CHECKING([whether struct shrink_control exists])
+	SPL_LINUX_TRY_COMPILE([
+		#include <linux/mm.h>
+	],[
+		struct shrink_control sc __attribute__ ((unused));
+
+		sc.nr_to_scan = 0;
+		sc.gfp_mask = GFP_KERNEL;
+	],[
+		AC_MSG_RESULT(yes)
+		AC_DEFINE(HAVE_SHRINK_CONTROL_STRUCT, 1,
+			[struct shrink_control exists])
+	],[
+		AC_MSG_RESULT(no)
+	])
+])