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

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Message-ID: <84721e8d-d40e-617c-b75e-ead51c3e1edf@nvidia.com>
Date:   Mon, 23 Jan 2023 19:11:42 -0800
From:   John Hubbard <jhubbard@...dia.com>
To:     David Howells <dhowells@...hat.com>,
        Al Viro <viro@...iv.linux.org.uk>,
        Christoph Hellwig <hch@...radead.org>,
        Jason Gunthorpe <jgg@...dia.com>
CC:     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 1/23/23 19:08, John Hubbard wrote:
> On 1/23/23 09:30, 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.
> 
> 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.

I see that I omitted both Jason's Cc and the reference, so I'll resend.
Sorry for the extra noise.

[1] https://lore.kernel.org/all/fcdb3294-3740-a0e0-b115-12842eb0696d@nvidia.com/

> 
> Also, I don't think that there is any large readability difference
> either way between 0x and <<1, so whatever you and Christophe settle on
> there seems fine.
> 
> So either way with those points,
> 
> Reviewed-by: John Hubbard <jhubbard@...dia.com>
> 
> thanks,

thanks,
-- 
John Hubbard
NVIDIA