linux-kernel - Re: [PATCH v8 07/10] block: Switch to pinning pages.

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Message-ID: <Y8/xApRVtqK7IlYT@infradead.org>
Date:   Tue, 24 Jan 2023 06:53:54 -0800
From:   Christoph Hellwig <hch@...radead.org>
To:     David Howells <dhowells@...hat.com>
Cc:     David Hildenbrand <david@...hat.com>,
        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>
Subject: Re: [PATCH v8 07/10] block: Switch to pinning pages.

On Tue, Jan 24, 2023 at 02:47:51PM +0000, David Howells wrote:
> > > +static inline void bio_set_cleanup_mode(struct bio *bio, struct iov_iter *iter)
> > > +{
> > > +	unsigned int cleanup_mode = iov_iter_extract_mode(iter);
> > > +
> > > +	if (cleanup_mode & FOLL_GET)
> > > +		bio_set_flag(bio, BIO_PAGE_REFFED);
> > > +	if (cleanup_mode & FOLL_PIN)
> > > +		bio_set_flag(bio, BIO_PAGE_PINNED);
> > 
> > Can FOLL_GET ever happen?
> 
> Yes - unless patches 8 and 9 are merged.  I had them as one, but Christoph
> split them up.

It can't.  Per your latest branch:

#define iov_iter_extract_mode(iter) (user_backed_iter(iter) ? FOLL_PIN : 0)