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

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Date:   Tue, 24 Jan 2023 10:00:28 -0400
From:   Jason Gunthorpe <jgg@...dia.com>
To:     David Howells <dhowells@...hat.com>
Cc:     John Hubbard <jhubbard@...dia.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

On Tue, Jan 24, 2023 at 01:57:08PM +0000, David Howells wrote:
> Jason Gunthorpe <jgg@...dia.com> wrote:
> 
> > I moved FOLL_PIN to internal.h because it is not supposed to be used
> > outside mm/*
> > 
> > I would prefer to keep it that way.
> 
> I'll need to do something else, then, such as creating a new pair of 'cleanup'
> flags:
> 
> 	[include/linux/mm_types.h]
> 	#define PAGE_CLEANUP_UNPIN	(1U << 0)
> 	#define PAGE_CLEANUP_PUT	(1U << 0)
> 
> 	[mm/gup.h]
> 	void folio_put_unpin(struct folio *folio, unsigned int cleanup_flags)
> 	{
> 		unsigned int gup_flags = 0;
> 
> 		cleanup_flags &= PAGE_CLEANUP_UNPIN | PAGE_CLEANUP_PUT;
> 		if (!cleanup_flags)
> 			return;
> 		gup_flags |= cleanup_flags & PAGE_CLEANUP_UNPIN ? FOLL_PIN : 0;
> 		gup_flags |= cleanup_flags & PAGE_CLEANUP_PUT ? FOLL_GET : 0;
> 		gup_put_folio(folio, 1, flags);
> 	}
> 	EXPORT_SYMBOL_GPL(folio_put_unpin);


I suggest:

if (cleanup_flags & PAGE_CLEANUP_UNPIN)
   gup_put_folio(folio, 1, true);
else if (cleanup_flags & PAGE_CLEANUP_PUT)
   gup_put_folio(folio, 1, false);

or if you are really counting cycles

if (cleanup_flags & PAGE_CLEANUP_NEEDED)
   gup_put_folio(folio, 1, cleanup_flags & PAGE_CLEANUP_UNPIN)

Jason