linux-kernel - Re: [PATCH v8 10/10] mm: Renumber FOLL_PIN and FOLL

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Message-ID: <545461.1674543956@warthog.procyon.org.uk>
Date:   Tue, 24 Jan 2023 07:05:56 +0000
From:   David Howells <dhowells@...hat.com>
To:     John Hubbard <jhubbard@...dia.com>
Cc:     dhowells@...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>,
        linux-mm@...ck.org
Subject: Re: [PATCH v8 10/10] mm: Renumber FOLL_PIN and FOLL_GET down

John Hubbard <jhubbard@...dia.com> 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.
> 
> Should we also get these sorted into internal-to-mm and public sets?
> Because Jason (+Cc) again was about to split them apart into
> mm/internal.h [1] and that might make that a little cleaner.

My plan was to push this patch by itself through akpm since it's only an
optimisation and not necessary to the rest of the patches here.

David