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 <[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? Sure, thanks for looking into it, will test it today. > > 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; > } > } > >
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