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 <[email protected]> > 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? commit a09ded8edf9ed4009930713e101249084cbcea5c Author: Kent Overstreet <[email protected]> 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 <[email protected]> Signed-off-by: Kent Overstreet <[email protected]> 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; } } -- To unsubscribe from this list: send the line "unsubscribe linux-bcache" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html
