From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755155Ab0JLGjv (ORCPT ); Tue, 12 Oct 2010 02:39:51 -0400 Received: from fgwmail6.fujitsu.co.jp ([192.51.44.36]:39423 "EHLO fgwmail6.fujitsu.co.jp" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753641Ab0JLGju (ORCPT ); Tue, 12 Oct 2010 02:39:50 -0400 X-SecurityPolicyCheck-FJ: OK by FujitsuOutboundMailChecker v1.4.0 Message-ID: <4CB40281.1020403@jp.fujitsu.com> Date: Tue, 12 Oct 2010 15:38:57 +0900 From: Yasuaki Ishimatsu User-Agent: Thunderbird 2.0.0.23 (Windows/20090812) MIME-Version: 1.0 To: axboe@kernel.dk, linux-kernel@vger.kernel.org Subject: [PATCH] blk: fix a wrong accounting of hd_struct->in_flight Content-Type: text/plain; charset=ISO-2022-JP Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Yasuaki Ishimatsu /proc/diskstats would display a strange output as follows. $ cat /proc/diskstats |grep sda 8 0 sda 90524 7579 102154 20464 0 0 0 0 0 14096 20089 8 1 sda1 19085 1352 21841 4209 0 0 0 0 4294967064 15689 4293424691 ~~~~~~~~~~ 8 2 sda2 71252 3624 74891 15950 0 0 0 0 232 23995 1562390 8 3 sda3 54 487 2188 92 0 0 0 0 0 88 92 8 4 sda4 4 0 8 0 0 0 0 0 0 0 0 8 5 sda5 81 2027 2130 138 0 0 0 0 0 87 137 Its reason is the wrong way of accounting hd_struct->in_flight. When a bio is merged into a request belongs to different partition by ELEVATOR_FRONT_MERGE. The detailed root cause is as follows. Assuming that there are two partition, sda1 and sda2. 1. A request for sda2 is in request_queue. Hence sda1's hd_struct->in_flight is 0 and sda2's one is 1. | hd_struct->in_flight --------------------------- sda1 | 0 sda2 | 1 --------------------------- 2. A bio belongs to sda1 is issued and is merged into the request mentioned on step1 by ELEVATOR_BACK_MERGE. The first sector of the request is changed from sda2 region to sda1 region. However the two partition's hd_struct->in_flight are not changed. | hd_struct->in_flight --------------------------- sda1 | 0 sda2 | 1 --------------------------- 3. The request is finished and blk_account_io_done() is called. In this case, sda2's hd_struct->in_flight, not a sda1's one, is decremented. | hd_struct->in_flight --------------------------- sda1 | -1 sda2 | 1 --------------------------- The patch fixes the problem. Signed-off-by: Yasuaki Ishimatsu --- block/blk-core.c | 12 ++++++++++++ 1 file changed, 12 insertions(+) Index: linux-2.6.36-rc7/block/blk-core.c =================================================================== --- linux-2.6.36-rc7.orig/block/blk-core.c 2010-10-07 05:39:52.000000000 +0900 +++ linux-2.6.36-rc7/block/blk-core.c 2010-10-09 05:53:51.000000000 +0900 @@ -1202,6 +1202,8 @@ static int __make_request(struct request const bool unplug = !!(bio->bi_rw & REQ_UNPLUG); const unsigned long ff = bio->bi_rw & REQ_FAILFAST_MASK; int rw_flags; + struct hd_struct *src_part; + struct hd_struct *dst_part; if ((bio->bi_rw & REQ_HARDBARRIER) && (q->next_ordered == QUEUE_ORDERED_NONE)) { @@ -1268,7 +1270,17 @@ static int __make_request(struct request * not touch req->buffer either... */ req->buffer = bio_data(bio); + src_part = disk_map_sector_rcu(req->rq_disk, blk_rq_pos(req)); req->__sector = bio->bi_sector; + dst_part = disk_map_sector_rcu(req->rq_disk, blk_rq_pos(req)); + if (unlikely(src_part != dst_part)) { + int rw = rq_data_dir(req); + + part_stat_lock(); + part_dec_in_flight(src_part, rw); + part_inc_in_flight(dst_part, rw); + part_stat_unlock(); + } req->__data_len += bytes; req->ioprio = ioprio_best(req->ioprio, prio); if (!blk_rq_cpu_valid(req))