linux-kernel - Re: [PATCH 1/2] mm/gup: Remove dead pgmap refcounting code

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Message-ID: <20250902120626.GA184112@ziepe.ca>
Date: Tue, 2 Sep 2025 09:06:26 -0300
From: Jason Gunthorpe <jgg@...pe.ca>
To: Alistair Popple <apopple@...dia.com>
Cc: linux-mm@...ck.org, akpm@...ux-foundation.org, david@...hat.com,
	osalvador@...e.de, jhubbard@...dia.com, peterx@...hat.com,
	linux-kernel@...r.kernel.org, dan.j.williams@...el.com
Subject: Re: [PATCH 1/2] mm/gup: Remove dead pgmap refcounting code

On Tue, Sep 02, 2025 at 03:14:20PM +1000, Alistair Popple wrote:
> Prior to aed877c2b425 ("device/dax: properly refcount device dax pages
> when mapping") ZONE_DEVICE pages were not fully reference counted when
> mapped into user page tables. Instead GUP would take a reference on the
> associated pgmap to ensure the results of pfn_to_page() remained valid.
> 
> This is no longer required and most of the code was removed by
> fd2825b0760a ("mm/gup: remove pXX_devmap usage from get_user_pages()").
> Finish cleaning this up by removing the dead calls to put_dev_pagemap()
> and the temporary context struct.
> 
> Signed-off-by: Alistair Popple <apopple@...dia.com>
> ---
>  mm/gup.c | 67 ++++++++++++++++++++++----------------------------------
>  1 file changed, 26 insertions(+), 41 deletions(-)

Reviewed-by: Jason Gunthorpe <jgg@...dia.com>

Yay! This never made alot of sense :\

Jason