linux-kernel - [PATCH] module: reorder kparam_array to remove alignment padding on 64 bit builds

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Message-ID: <1298481296.2130.7.camel@castor.rsk>
Date:	Wed, 23 Feb 2011 17:14:56 +0000
From:	Richard Kennedy <richard@....demon.co.uk>
To:	Rusty Russell <rusty@...tcorp.com.au>
Cc:	lkml <linux-kernel@...r.kernel.org>
Subject: [PATCH] module: reorder kparam_array to remove alignment padding
 on 64 bit builds

Reorder structure kparam_array to remove 8 bytes of alignment padding on
64 bit builds, dropping its size from 40 to 32 bytes.

Also update the macro module_param_array_named to initialise the
structure using its member names to allow it to be changed without
touching all its call sites.

'git grep' finds module_param_array in 1037 places so this patch will
save a small amount of data space across many modules.

Signed-off-by: Richard Kennedy <richard@....demon.co.uk>
----

patch against v2.6.38-rc6
compiled & tested on x86_64

regards
Richard



diff --git a/include/linux/moduleparam.h b/include/linux/moduleparam.h
index 07b4195..ddaae98 100644
--- a/include/linux/moduleparam.h
+++ b/include/linux/moduleparam.h
@@ -67,9 +67,9 @@ struct kparam_string {
 struct kparam_array
 {
 	unsigned int max;
+	unsigned int elemsize;
 	unsigned int *num;
 	const struct kernel_param_ops *ops;
-	unsigned int elemsize;
 	void *elem;
 };
 
@@ -371,8 +371,9 @@ extern int param_get_invbool(char *buffer, const struct kernel_param *kp);
  */
 #define module_param_array_named(name, array, type, nump, perm)		\
 	static const struct kparam_array __param_arr_##name		\
-	= { ARRAY_SIZE(array), nump, &param_ops_##type,			\
-	    sizeof(array[0]), array };					\
+	= { .max = ARRAY_SIZE(array), .num = nump,                      \
+	    .ops = &param_ops_##type,					\
+	    .elemsize = sizeof(array[0]), .elem = array };		\
 	__module_param_call(MODULE_PARAM_PREFIX, name,			\
 			    &param_array_ops,				\
 			    .arr = &__param_arr_##name,			\


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