From: Andrew Morton <akpm@osdl.org>

Attempt to account for filesytem metadata reads.

Doing it in ll_rw_block() is super-simple and is in fact pretty accurate (I
think).  For example, it accounts for those little reads which
__block_prepare_write() needs to do to bring internal buffer_heads up to date.

But if any filesystem uses ll_rw_block() for its main ->readpage[s]() or
->writepage[s]() implementation, we'll double-account like mad.

Cc: Jay Lan <jlan@sgi.com>
Cc: Shailabh Nagar <nagar@watson.ibm.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Chris Sturtivant <csturtiv@sgi.com>
Cc: Tony Ernst <tee@sgi.com>
Cc: Guillaume Thouvenin <guillaume.thouvenin@bull.net>
Signed-off-by: Andrew Morton <akpm@osdl.org>
---

 fs/buffer.c |    3 +++
 1 file changed, 3 insertions(+)

diff -puN fs/buffer.c~io-accounting-metadata-read-accounting fs/buffer.c
--- a/fs/buffer.c~io-accounting-metadata-read-accounting
+++ a/fs/buffer.c
@@ -2721,6 +2721,9 @@ void ll_rw_block(int rw, int nr, struct 
 {
 	int i;
 
+	if (likely(nr) && !(rw & WRITE))
+		task_io_account_read(nr * bhs[0]->b_size);
+
 	for (i = 0; i < nr; i++) {
 		struct buffer_head *bh = bhs[i];
 
_