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Message-ID: <Y87RFUQcN4my7pa9@infradead.org>
Date: Mon, 23 Jan 2023 10:25:25 -0800
From: Christoph Hellwig <hch@...radead.org>
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>,
linux-mm@...ck.org
Subject: Re: [PATCH v8 10/10] mm: Renumber FOLL_PIN and FOLL_GET down
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@....de>
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