fs: drop_caches: move sysctl to fs/drop_caches.c

The sysctl_drop_caches to fs/drop_caches.c, move it to
fs/drop_caches.c from /kernel/sysctl.c. And remove the
useless extern variable declaration from include/linux/mm.h

Signed-off-by: Kaixiong Yu <[e-mail]>
Reviewed-by: Kees Cook <[e-mail]>
Reviewed-by: Jan Kara <[e-mail]>
Reviewed-by: Christian Brauner <[e-mail]>
Reviewed-by: Jeff Layton <[e-mail]>
Signed-off-by: Joel Granados <[e-mail]>

fs/drop_caches.c

···
 #include "internal.h"
 
 /* A global variable is a bit ugly, but it keeps the code simple */
-int sysctl_drop_caches;
+static int sysctl_drop_caches;
 
 static void drop_pagecache_sb(struct super_block *sb, void *unused)
 {
···
 	iput(toput_inode);
 }
 
-int drop_caches_sysctl_handler(const struct ctl_table *table, int write,
+static int drop_caches_sysctl_handler(const struct ctl_table *table, int write,
 		void *buffer, size_t *length, loff_t *ppos)
 {
 	int ret;
···
 	}
 	return 0;
 }
+
+static const struct ctl_table drop_caches_table[] = {
+	{
+		.procname	= "drop_caches",
+		.data		= &sysctl_drop_caches,
+		.maxlen		= sizeof(int),
+		.mode		= 0200,
+		.proc_handler	= drop_caches_sysctl_handler,
+		.extra1		= SYSCTL_ONE,
+		.extra2		= SYSCTL_FOUR,
+	},
+};
+
+static int __init init_vm_drop_caches_sysctls(void)
+{
+	register_sysctl_init("vm", drop_caches_table);
+	return 0;
+}
+fs_initcall(init_vm_drop_caches_sysctls);

include/linux/mm.h

···
 
 extern bool process_shares_mm(struct task_struct *p, struct mm_struct *mm);
 
-#ifdef CONFIG_SYSCTL
-extern int sysctl_drop_caches;
-int drop_caches_sysctl_handler(const struct ctl_table *, int, void *, size_t *,
-		loff_t *);
-#endif
-
 void drop_slab(void);
 
 #ifndef CONFIG_MMU

kernel/sysctl.c

···
 
 static const struct ctl_table vm_table[] = {
 	{
-		.procname	= "drop_caches",
-		.data		= &sysctl_drop_caches,
-		.maxlen		= sizeof(int),
-		.mode		= 0200,
-		.proc_handler	= drop_caches_sysctl_handler,
-		.extra1		= SYSCTL_ONE,
-		.extra2		= SYSCTL_FOUR,
-	},
-	{
 		.procname	= "vfs_cache_pressure",
 		.data		= &sysctl_vfs_cache_pressure,
 		.maxlen		= sizeof(sysctl_vfs_cache_pressure),