Re: [PATCH v7 6/8] block: Make bio structs pin pages rather than ref'ing if appropriate

[Christoph Hellwig]

This really does three things:
 
 1) add the BIO_PAGE_PINNED infrastructure
 2) convert bio_iov_iter_get_pages to use iov_iter_extract_pages
 3) convert bio_map_user_iov to use iov_iter_extract_pages

so it should be three pages, with the first one also containing
what is in your previous patch.

> @@ -1183,7 +1185,7 @@ void __bio_release_pages(struct bio *bio, bool mark_dirty)
>  	bio_for_each_segment_all(bvec, bio, iter_all) {
>  		if (mark_dirty && !PageCompound(bvec->bv_page))
>  			set_page_dirty_lock(bvec->bv_page);
> -		put_page(bvec->bv_page);
> +		bio_release_page(bio, bvec->bv_page);

This can be micro-optimized a bit by only doing the flags conversion
once.