On Mon, May 25, 2015 at 5:04 PM, Christoph Hellwig <h...@lst.de> wrote: > On Fri, May 22, 2015 at 11:18:40AM -0700, Ming Lin wrote: >> From: Kent Overstreet <kent.overstr...@gmail.com> >> >> As generic_make_request() is now able to handle arbitrarily sized bios, >> it's no longer necessary for each individual block driver to define its >> own ->merge_bvec_fn() callback. Remove every invocation completely. > > It might be good to replace patch 1 and this one by a patch per driver > to remove the merge_bvec_fn instance and add the blk_queue_split call > for all those drivers that actually had a ->merge_bvec_fn. As some > of them were non-trivial attention from the maintainers would be helpful, > and a patch per driver might help with that. > >> -/* This is called by bio_add_page(). >> - * >> - * q->max_hw_sectors and other global limits are already enforced there. >> - * >> - * We need to call down to our lower level device, >> - * in case it has special restrictions. >> - * >> - * We also may need to enforce configured max-bio-bvecs limits. >> - * >> - * As long as the BIO is empty we have to allow at least one bvec, >> - * regardless of size and offset, so no need to ask lower levels. >> - */ >> -int drbd_merge_bvec(struct request_queue *q, struct bvec_merge_data *bvm, >> struct bio_vec *bvec) > > > This just checks the lower device, so it looks obviously fine. > >> -static int pkt_merge_bvec(struct request_queue *q, struct bvec_merge_data >> *bmd, >> - struct bio_vec *bvec) >> -{ >> - struct pktcdvd_device *pd = q->queuedata; >> - sector_t zone = get_zone(bmd->bi_sector, pd); >> - int used = ((bmd->bi_sector - zone) << 9) + bmd->bi_size; >> - int remaining = (pd->settings.size << 9) - used; >> - int remaining2; >> - >> - /* >> - * A bio <= PAGE_SIZE must be allowed. If it crosses a packet >> - * boundary, pkt_make_request() will split the bio. >> - */ >> - remaining2 = PAGE_SIZE - bmd->bi_size; >> - remaining = max(remaining, remaining2); >> - >> - BUG_ON(remaining < 0); >> - return remaining; >> -} > > As mentioned in the comment pkt_make_request will split the bio so pkt > looks fine. > >> diff --git a/drivers/block/rbd.c b/drivers/block/rbd.c >> index ec6c5c6..f50edb3 100644 >> --- a/drivers/block/rbd.c >> +++ b/drivers/block/rbd.c >> @@ -3440,52 +3440,6 @@ static int rbd_queue_rq(struct blk_mq_hw_ctx *hctx, >> return BLK_MQ_RQ_QUEUE_OK; >> } >> >> -/* >> - * a queue callback. Makes sure that we don't create a bio that spans across >> - * multiple osd objects. One exception would be with a single page bios, >> - * which we handle later at bio_chain_clone_range() >> - */ >> -static int rbd_merge_bvec(struct request_queue *q, struct bvec_merge_data >> *bmd, >> - struct bio_vec *bvec) > > It seems rbd handles requests spanning objects just fine, so I don't > really understand why rbd_merge_bvec even exists. Getting some form > of ACK from the ceph folks would be useful.
I'm not Alex, but yeah, we have all the clone/split machinery and so we can handle a spanning case just fine. I think rbd_merge_bvec() exists to make sure we don't have to do that unless it's really necessary - like when a single page gets submitted at an inconvenient offset. I have a patch that adds a blk_queue_chunk_sectors(object_size) call to rbd_init_disk() but I haven't had a chance to play with it yet. In any case, we should be fine with getting rid of rbd_merge_bvec(). If this ends up a per-driver patchset, I can make rbd_merge_bvec() -> blk_queue_chunk_sectors() a single patch and push it through ceph-client.git. Thanks, Ilya -- To unsubscribe from this list: send the line "unsubscribe ceph-devel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html