linux-kernel - Re: [PATCH v4 7/7] iov_iter, block: Make bio structs pin pages rather than ref'ing if appropriate

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Message-ID: <2155893.1673361724@warthog.procyon.org.uk>
Date:   Tue, 10 Jan 2023 14:42:04 +0000
From:   David Howells <dhowells@...hat.com>
To:     Jan Kara <jack@...e.cz>
Cc:     dhowells@...hat.com, Jens Axboe <axboe@...nel.dk>,
        Al Viro <viro@...iv.linux.org.uk>,
        Christoph Hellwig <hch@....de>,
        Matthew Wilcox <willy@...radead.org>,
        Logan Gunthorpe <logang@...tatee.com>,
        Christoph Hellwig <hch@...radead.org>,
        Jeff Layton <jlayton@...nel.org>,
        linux-fsdevel@...r.kernel.org, linux-block@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 7/7] iov_iter, block: Make bio structs pin pages rather than ref'ing if appropriate

Jan Kara <jack@...e.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