On 2013年04月22日 23:46, Kent Overstreet wrote:
> On Wed, Apr 17, 2013 at 09:36:11AM +0200, Jack Wang wrote:
>> We are using your bcache-testing branch.
>>
>> From 20ad8cfb8047df2d09a5a960610f02c555a31a4f Mon Sep 17 00:00:00 2001
>> From: Jack Wang <jinpu.wang@xxxxxxxxxxxxxxxx>
>> Date: Tue, 16 Apr 2013 14:59:04 +0200
>> Subject: [PATCH] limit the max sectors in bcache to fix the make request bug
>> in raid10
>> During test bcache with raid1+0, we saw a lot of complain as below:
>> [ 2766.555172] md/raid0:md400: make_request bug: can't convert block
>> across chunks or bigger than 512k 953328 144
>>
>> when the using dd or fio with bigger blocksize like 512k, limited the
>> bio_max_sectors resolve this issue.
>
> The fix is wrong - it'll have the effect of limiting _every_ bio bcache
> emits to a single page, which will be bad for performance.
>
> I think I just found the problem though - looking at the raid0
> merge_bvec_fn, when it's stacked on top of devices with their own
> merge_bvec_fns, it reuses the bvm was passed to it and modifies the
> bi_bdev and bi_sector. Ew.
>
> Can you try this patch and see if it fixes it?
Sure, thanks for looking into it, will test it today.
>
> commit a09ded8edf9ed4009930713e101249084cbcea5c
> Author: Kent Overstreet <koverstreet@xxxxxxxxxx>
> Date: Mon Apr 22 14:44:24 2013 -0700
>
> bcache: Fix merge_bvec_fn usage for when it modifies the bvm
>
> Stacked md devices reuse the bvm for the subordinate device, causing
> problems...
>
> Reported-by: Michael Balser <michael.balser@xxxxxxxxxxxxxxxx>
> Signed-off-by: Kent Overstreet <koverstreet@xxxxxxxxxx>
>
> diff --git a/drivers/md/bcache/io.c b/drivers/md/bcache/io.c
> index 5304eaa..48efd4d 100644
> --- a/drivers/md/bcache/io.c
> +++ b/drivers/md/bcache/io.c
> @@ -163,13 +163,6 @@ static unsigned bch_bio_max_sectors(struct bio *bio)
> struct bio_vec *bv, *end = bio_iovec(bio) +
> min_t(int, bio_segments(bio), max_segments);
>
> - struct bvec_merge_data bvm = {
> - .bi_bdev = bio->bi_bdev,
> - .bi_sector = bio->bi_sector,
> - .bi_size = 0,
> - .bi_rw = bio->bi_rw,
> - };
> -
> if (bio->bi_rw & REQ_DISCARD)
> return min(ret, q->limits.max_discard_sectors);
>
> @@ -178,12 +171,18 @@ static unsigned bch_bio_max_sectors(struct bio *bio)
> ret = 0;
>
> for (bv = bio_iovec(bio); bv < end; bv++) {
> + struct bvec_merge_data bvm = {
> + .bi_bdev = bio->bi_bdev,
> + .bi_sector = bio->bi_sector,
> + .bi_size = ret << 9,
> + .bi_rw = bio->bi_rw,
> + };
> +
> if (q->merge_bvec_fn &&
> q->merge_bvec_fn(q, &bvm, bv) < (int) bv->bv_len)
> break;
>
> - ret += bv->bv_len >> 9;
> - bvm.bi_size += bv->bv_len;
> + ret += bv->bv_len >> 9;
> }
> }
>
>
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