[PATCH v4 09/13] bcache: fix inaccurate io state for detached bcache devices

Coly Li
2018-01-28T07:48:15Z

From: Tang Junhui <tang.junhui@zte.com.cn>

When we run IO in a detached device, and run iostat to shows IO status,
normally it will show like bellow (Omitted some fields):
Device: ... avgrq-sz avgqu-sz await r_await w_await svctm %util
sdd ... 15.89 0.53 1.82 0.20 2.23 1.81 52.30
bcache0 ... 15.89 115.42 0.00 0.00 0.00 2.40 69.60
but after IO stopped, there are still very big avgqu-sz and %util
values as bellow:
Device: ... avgrq-sz avgqu-sz await r_await w_await svctm %util
bcache0 ... 0 5326.32 0.00 0.00 0.00 0.00 100.10

The reason for this issue is that, only generic_start_io_acct() called
and no generic_end_io_acct() called for detached device in
cached_dev_make_request(). See the code:
//start generic_start_io_acct()
generic_start_io_acct(q, rw, bio_sectors(bio), &d->disk->part0);
if (cached_dev_get(dc)) {
//will callback generic_end_io_acct()
}
else {
//will not call generic_end_io_acct()
}

This patch calls generic_end_io_acct() in the end of IO for detached
devices, so we can show IO state correctly.

(Modified to use GFP_NOIO in kzalloc() by Coly Li)

Signed-off-by: Tang Junhui <tang.junhui@zte.com.cn>
Reviewed-by: Coly Li <colyli@suse.de>
Reviewed-by: Hannes Reinecke <hare@suse.com>
---
drivers/md/bcache/request.c | 58 +++++++++++++++++++++++++++++++++++++++------
1 file changed, 51 insertions(+), 7 deletions(-)

diff --git a/drivers/md/bcache/request.c b/drivers/md/bcache/request.c
index 02296bda6384..e09c5ae745be 100644
--- a/drivers/md/bcache/request.c
+++ b/drivers/md/bcache/request.c
@@ -986,6 +986,55 @@ static void cached_dev_nodata(struct closure *cl)
continue_at(cl, cached_dev_bio_complete, NULL);
}

+struct detached_dev_io_private {
+ struct bcache_device *d;
+ unsigned long start_time;
+ bio_end_io_t *bi_end_io;
+ void *bi_private;
+};
+
+static void detatched_dev_end_io(struct bio *bio)
+{
+ struct detached_dev_io_private *ddip;
+
+ ddip = bio->bi_private;
+ bio->bi_end_io = ddip->bi_end_io;
+ bio->bi_private = ddip->bi_private;
+
+ generic_end_io_acct(ddip->d->disk->queue,
+ bio_data_dir(bio),
+ &ddip->d->disk->part0, ddip->start_time);
+
+ kfree(ddip);
+
+ bio->bi_end_io(bio);
+}
+
+static void detached_dev_do_request(struct bcache_device *d, struct bio *bio)
+{
+ struct detached_dev_io_private *ddip;
+ struct cached_dev *dc = container_of(d, struct cached_dev, disk);
+
+ /*
+ * no need to call closure_get(&dc->disk.cl),
+ * because upper layer had already opened bcache device,
+ * which would call closure_get(&dc->disk.cl)
+ */
+ ddip = kzalloc(sizeof(struct detached_dev_io_private), GFP_NOIO);
+ ddip->d = d;
+ ddip->start_time = jiffies;
+ ddip->bi_end_io = bio->bi_end_io;
+ ddip->bi_private = bio->bi_private;
+ bio->bi_end_io = detatched_dev_end_io;
+ bio->bi_private = ddip;
+
+ if ((bio_op(bio) == REQ_OP_DISCARD) &&
+ !blk_queue_discard(bdev_get_queue(dc->bdev)))
+ bio->bi_end_io(bio);
+ else
+ generic_make_request(bio);
+}
+
/* Cached devices - read & write stuff */

static blk_qc_t cached_dev_make_request(struct request_queue *q,
@@ -1028,13 +1077,8 @@ static blk_qc_t cached_dev_make_request(struct request_queue *q,
else
cached_dev_read(dc, s);
}
- } else {
- if ((bio_op(bio) == REQ_OP_DISCARD) &&
- !blk_queue_discard(bdev_get_queue(dc->bdev)))
- bio_endio(bio);
- else
- generic_make_request(bio);
- }
+ } else
+ detached_dev_do_request(d, bio);

return BLK_QC_T_NONE;
}
--
2.15.1