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From:   David Howells <dhowells@redhat.com>
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To:     Jan Kara <jack@suse.cz>
Cc:     dhowells@redhat.com, Jens Axboe <axboe@kernel.dk>,
        Al Viro <viro@zeniv.linux.org.uk>,
        Christoph Hellwig <hch@lst.de>,
        Matthew Wilcox <willy@infradead.org>,
        Logan Gunthorpe <logang@deltatee.com>,
        Christoph Hellwig <hch@infradead.org>,
        Jeff Layton <jlayton@kernel.org>,
        linux-fsdevel@vger.kernel.org, linux-block@vger.kernel.org,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH v4 7/7] iov_iter, block: Make bio structs pin pages rather than ref'ing if appropriate
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Date:   Tue, 10 Jan 2023 14:42:04 +0000
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Jan Kara <jack@suse.cz> wrote:

> ... So filesystems really need DIO reads to use FOLL_PIN instead of FOLL_GET
> and consequently we need to pass information to bio completion function how
> page references should be dropped.

That information would be available in the bio struct with this patch if
necessary, though transcribed into a combination of BIO_* flags instead off
FOLL_* flags.

I wonder if there's the possibility of the filesystem that generated the bio
nicking the pages out of the bio and putting them itself.

David