Re: [PATCH V10 14/19] block: enable multipage bvecs

Christoph Hellwig
2018-11-16T13:53:13Z

> -
> - if (page == bv->bv_page && off == bv->bv_offset + bv->bv_len) {
> - bv->bv_len += len;
> - bio->bi_iter.bi_size += len;
> - return true;
> - }
> + struct request_queue *q = NULL;
> +
> + if (page == bv->bv_page && off == (bv->bv_offset + bv->bv_len)
> + && (off + len) <= PAGE_SIZE)

How could the page struct be the same, but the range beyond PAGE_SIZE
(at least with the existing callers)?

Also no need for the inner btraces, and the && always goes on the
first line.

> + if (bio->bi_disk)
> + q = bio->bi_disk->queue;
> +
> + /* disable multi-page bvec too if cluster isn't enabled */
> + if (!q || !blk_queue_cluster(q) ||
> + ((page_to_phys(bv->bv_page) + bv->bv_offset + bv->bv_len) !=
> + (page_to_phys(page) + off)))
> + return false;
> + merge:
> + bv->bv_len += len;
> + bio->bi_iter.bi_size += len;
> + return true;

Ok, this is scary, as it will give differen results depending on when
bi_disk is assigned. But then again we shouldn't really do the cluster
check here, but rather when splitting the bio for the actual low-level
driver.

(and eventually we should kill this clustering setting off in favor
of our normal segment limits).