Re: [RFC PATCH v2 3/3] block: Use iov_iter_extract_pages() and page pinning in direct-io.c

From: Christoph Hellwig
Date: Fri May 26 2023 - 04:26:16 EST

On Thu, May 25, 2023 at 11:39:53PM +0100, David Howells wrote:
> Change the old block-based direct-I/O code to use iov_iter_extract_pages()
> to pin user pages or leave kernel pages unpinned rather than taking refs
> when submitting bios.
> This makes use of the preceding patches to not take pins on the zero page
> (thereby allowing insertion of zero pages in with pinned pages) and to get
> additional pins on pages, allowing an extracted page to be used in multiple
> bios without having to re-extract it.

I'm not seeing where we skip the unpin of the zero page, as commented
in patch 1 (but maybe I'm not reviewing carefully enough as I'm at a
conference right now).

Otherwise my only rather cosmetic comment right now is that I'd called
the "need_unpin" member is_pinned.