linux-kernel - Re: [PATCH v8 02/10] iov_iter: Add a function to extract a page list from an iterator

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Date:   Tue, 24 Jan 2023 15:37:43 +0100
From:   David Hildenbrand <david@...hat.com>
To:     David Howells <dhowells@...hat.com>
Cc:     Al Viro <viro@...iv.linux.org.uk>,
        Christoph Hellwig <hch@...radead.org>,
        Matthew Wilcox <willy@...radead.org>,
        Jens Axboe <axboe@...nel.dk>, Jan Kara <jack@...e.cz>,
        Jeff Layton <jlayton@...nel.org>,
        Logan Gunthorpe <logang@...tatee.com>,
        linux-fsdevel@...r.kernel.org, linux-block@...r.kernel.org,
        linux-kernel@...r.kernel.org, Christoph Hellwig <hch@....de>,
        John Hubbard <jhubbard@...dia.com>, linux-mm@...ck.org
Subject: Re: [PATCH v8 02/10] iov_iter: Add a function to extract a page list
 from an iterator

On 24.01.23 15:35, David Howells wrote:
> David Hildenbrand <david@...hat.com> wrote:
> 
>>> +#define iov_iter_extract_mode(iter) (user_backed_iter(iter) ? FOLL_PIN : 0)
>>> +
>>
>> Does it make sense to move that to the patch where it is needed? (do we need
>> it at all anymore?)
> 
> Yes, we need something.  Granted, there are now only two alternatives, not
> three: either the pages are going to be pinned or they're not going to be
> pinned, but I would rather have a specific function that tells you than just
> use, say, user_backed_iter() to make it easier to adjust it later if we need
> to - and easier to find the places where we need to adjust.
> 
> But if it's preferred we could require people to use user_backed_iter()
> instead.

At least reduces the occurrences of FOLL_PIN :)

-- 
Thanks,

David / dhildenb