linux-kernel - Re: [RFC PATCH v2 3/3] block: Use iov_iter_extract

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Message-ID: <ZHBtGJ3SzJtr5HZP@infradead.org>
Date:   Fri, 26 May 2023 01:26:00 -0700
From:   Christoph Hellwig <hch@...radead.org>
To:     David Howells <dhowells@...hat.com>
Cc:     Christoph Hellwig <hch@...radead.org>,
        David Hildenbrand <david@...hat.com>,
        Jens Axboe <axboe@...nel.dk>,
        Al Viro <viro@...iv.linux.org.uk>,
        Matthew Wilcox <willy@...radead.org>, Jan Kara <jack@...e.cz>,
        Jeff Layton <jlayton@...nel.org>,
        Jason Gunthorpe <jgg@...dia.com>,
        Logan Gunthorpe <logang@...tatee.com>,
        Hillf Danton <hdanton@...a.com>,
        Christian Brauner <brauner@...nel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        linux-fsdevel@...r.kernel.org, linux-block@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [RFC PATCH v2 3/3] block: Use iov_iter_extract_pages() and page
 pinning in direct-io.c

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.