fs: Convert nr_inodes and nr_unused to per-cpu counters

The number of inodes allocated does not need to be tied to the
addition or removal of an inode to/from a list. If we are not tied
to a list lock, we could update the counters when inodes are
initialised or destroyed, but to do that we need to convert the
counters to be per-cpu (i.e. independent of a lock). This means that
we have the freedom to change the list/locking implementation
without needing to care about the counters.

Based on a patch originally from Eric Dumazet.

[AV: cleaned up a bit, fixed build breakage on weird configs

Signed-off-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
diff --git a/kernel/sysctl.c b/kernel/sysctl.c
index 694b140..99a510c 100644
--- a/kernel/sysctl.c
+++ b/kernel/sysctl.c
@@ -1340,14 +1340,14 @@
 		.data		= &inodes_stat,
 		.maxlen		= 2*sizeof(int),
 		.mode		= 0444,
-		.proc_handler	= proc_dointvec,
+		.proc_handler	= proc_nr_inodes,
 	},
 	{
 		.procname	= "inode-state",
 		.data		= &inodes_stat,
 		.maxlen		= 7*sizeof(int),
 		.mode		= 0444,
-		.proc_handler	= proc_dointvec,
+		.proc_handler	= proc_nr_inodes,
 	},
 	{
 		.procname	= "file-nr",