Date:   Mon, 23 Jan 2023 10:25:25 -0800
From:   Christoph Hellwig <hch@infradead.org>
To:     David Howells <dhowells@redhat.com>
Cc:     Al Viro <viro@zeniv.linux.org.uk>,
        Christoph Hellwig <hch@infradead.org>,
        Matthew Wilcox <willy@infradead.org>,
        Jens Axboe <axboe@kernel.dk>, Jan Kara <jack@suse.cz>,
        Jeff Layton <jlayton@kernel.org>,
        Logan Gunthorpe <logang@deltatee.com>,
        linux-fsdevel@vger.kernel.org, linux-block@vger.kernel.org,
        linux-kernel@vger.kernel.org, Christoph Hellwig <hch@lst.de>,
        linux-mm@kvack.org
Subject: Re: [PATCH v8 10/10] mm: Renumber FOLL_PIN and FOLL_GET down
Message-ID: <Y87RFUQcN4my7pa9@infradead.org>
References: <20230123173007.325544-1-dhowells@redhat.com>
 <20230123173007.325544-11-dhowells@redhat.com>
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On Mon, Jan 23, 2023 at 05:30:07PM +0000, David Howells wrote:
> Renumber FOLL_PIN and FOLL_GET down to bit 0 and 1 respectively so that
> they are coincidentally the same as BIO_PAGE_PINNED and BIO_PAGE_REFFED and
> also so that they can be stored in the bottom two bits of a page pointer
> (something I'm looking at for zerocopy socket fragments).
> 
> (Note that BIO_PAGE_REFFED should probably be got rid of at some point,
> hence why FOLL_PIN is at 0.)
> 
> Also renumber down the other FOLL_* flags to close the gaps.

Taking the risk of having a long bikeshed:  I much prefer (1U << bitnr)
style definition that make it obvious where there are holes, but
otherwise:

Reviewed-by: Christoph Hellwig <hch@lst.de>