Re: [PATCH v2 16/25] iomap: Support large pages in read paths

[Christoph Hellwig]

> +/*
> + * Estimate the number of vectors we need based on the current page size;
> + * if we're wrong we'll end up doing an overly large allocation or needing
> + * to do a second allocation, neither of which is a big deal.
> + */
> +static unsigned int iomap_nr_vecs(struct page *page, loff_t length)
> +{
> +	return (length + thp_size(page) - 1) >> page_shift(page);
> +}

With the multipage bvecs a huge page (or any physically contigous piece
of memory) will always use one or less (if merged into the previous)
bio_vec.  So this can be simplified and optimized.