On Tue, 3 Jul 2012 14:23:41 +0800 majianpeng <majianpeng@xxxxxxxxx> wrote:
> Because bios will merge at block-layer,so bios-error may caused by other
> bio which be merged into to the same request.
> Using this flag,it will find exactly error-sector and not do redundant
> operation like re-write and re-read.
>
> Signed-off-by: majianpeng <majianpeng@xxxxxxxxx>
Hi,
I think this patch needs a more detailed explanation.
What exactly is the situation that causes a problem, and what exactly is the
problem that it causes?
Pretend that I don't know anything about what happens below the md level..
Thanks,
NeilBrown
> ---
> block/blk-core.c | 8 ++++++++
> drivers/md/raid5.c | 16 +++++++++++++---
> drivers/md/raid5.h | 1 +
> 3 files changed, 22 insertions(+), 3 deletions(-)
>
> diff --git a/block/blk-core.c b/block/blk-core.c
> index 3c923a7..ee04bfc 100644
> --- a/block/blk-core.c
> +++ b/block/blk-core.c
> @@ -1401,6 +1401,9 @@ void init_request_from_bio(struct request *req, struct bio *bio)
> if (bio->bi_rw & REQ_RAHEAD)
> req->cmd_flags |= REQ_FAILFAST_MASK;
>
> + if (unlikely(bio->bi_rw & REQ_NOMERGE))
> + req->cmd_flags |= REQ_NOMERGE;
> +
> req->errors = 0;
> req->__sector = bio->bi_sector;
> req->ioprio = bio_prio(bio);
> @@ -1428,6 +1431,11 @@ void blk_queue_bio(struct request_queue *q, struct bio *bio)
> goto get_rq;
> }
>
> + if (unlikely(bio->bi_rw & REQ_NOMERGE)) {
> + spin_lock_irq(q->queue_lock);
> + where = ELEVATOR_INSERT_BACK;
> + goto get_rq;
> + }
> /*
> * Check if we can merge with the plugged list before grabbing
> * any locks.
> diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c
> index d267672..04f78d2 100644
> --- a/drivers/md/raid5.c
> +++ b/drivers/md/raid5.c
> @@ -632,6 +632,9 @@ static void ops_run_io(struct stripe_head *sh, struct stripe_head_state *s)
> else
> bi->bi_sector = (sh->sector
> + rdev->data_offset);
> + if (test_bit(R5_ReadNoMerge, &sh->dev[i].flags))
> + bi->bi_rw |= REQ_NOMERGE;
> +
> bi->bi_flags = 1 << BIO_UPTODATE;
> bi->bi_idx = 0;
> bi->bi_io_vec[0].bv_len = STRIPE_SIZE;
> @@ -1731,7 +1734,9 @@ static void raid5_end_read_request(struct bio * bi, int error)
> atomic_add(STRIPE_SECTORS, &rdev->corrected_errors);
> clear_bit(R5_ReadError, &sh->dev[i].flags);
> clear_bit(R5_ReWrite, &sh->dev[i].flags);
> - }
> + } else if (test_bit(R5_ReadNoMerge, &sh->dev[i].flags))
> + clear_bit(R5_ReadNoMerge, &sh->dev[i].flags);
> +
> if (atomic_read(&rdev->read_errors))
> atomic_set(&rdev->read_errors, 0);
> } else {
> @@ -1773,7 +1778,11 @@ static void raid5_end_read_request(struct bio * bi, int error)
> else
> retry = 1;
> if (retry)
> - set_bit(R5_ReadError, &sh->dev[i].flags);
> + if (test_bit(R5_ReadNoMerge, &sh->dev[i].flags)) {
> + set_bit(R5_ReadError, &sh->dev[i].flags);
> + clear_bit(R5_ReadNoMerge, &sh->dev[i].flags);
> + } else
> + set_bit(R5_ReadNoMerge, &sh->dev[i].flags);
> else {
> clear_bit(R5_ReadError, &sh->dev[i].flags);
> clear_bit(R5_ReWrite, &sh->dev[i].flags);
> @@ -4481,7 +4490,8 @@ static int retry_aligned_read(struct r5conf *conf, struct bio *raid_bio)
> conf->retry_read_aligned = raid_bio;
> return handled;
> }
> -
> + if (likely(raid_bio->bi_size >> 9) > STRIPE_SECTORS)
> + set_bit(R5_ReadNoMerge, &sh->dev[dd_idx].flags);
> handle_stripe(sh);
> release_stripe(sh);
> handled++;
> diff --git a/drivers/md/raid5.h b/drivers/md/raid5.h
> index 2164021..6767d07 100644
> --- a/drivers/md/raid5.h
> +++ b/drivers/md/raid5.h
> @@ -273,6 +273,7 @@ enum r5dev_flags {
> R5_Wantwrite,
> R5_Overlap, /* There is a pending overlapping request
> * on this block */
> + R5_ReadNoMerge, /* prevent bio from merging in block-layer */
> R5_ReadError, /* seen a read error here recently */
> R5_ReWrite, /* have tried to over-write the readerror */
>
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