linux-ext4 - Re: [PATCH 06/12] mm/gup: Remove pXX_devmap usage from get_user

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Message-ID: <6840fb3848258_24911003e@dwillia2-xfh.jf.intel.com.notmuch>
Date: Wed, 4 Jun 2025 19:04:40 -0700
From: Dan Williams <dan.j.williams@...el.com>
To: Alistair Popple <apopple@...dia.com>, <linux-mm@...ck.org>
CC: Alistair Popple <apopple@...dia.com>, <gerald.schaefer@...ux.ibm.com>,
	<dan.j.williams@...el.com>, <jgg@...pe.ca>, <willy@...radead.org>,
	<david@...hat.com>, <linux-kernel@...r.kernel.org>, <nvdimm@...ts.linux.dev>,
	<linux-fsdevel@...r.kernel.org>, <linux-ext4@...r.kernel.org>,
	<linux-xfs@...r.kernel.org>, <jhubbard@...dia.com>, <hch@....de>,
	<zhang.lyra@...il.com>, <debug@...osinc.com>, <bjorn@...nel.org>,
	<balbirs@...dia.com>, <lorenzo.stoakes@...cle.com>,
	<linux-arm-kernel@...ts.infradead.org>, <loongarch@...ts.linux.dev>,
	<linuxppc-dev@...ts.ozlabs.org>, <linux-riscv@...ts.infradead.org>,
	<linux-cxl@...r.kernel.org>, <dri-devel@...ts.freedesktop.org>,
	<John@...ves.net>
Subject: Re: [PATCH 06/12] mm/gup: Remove pXX_devmap usage from
 get_user_pages()

Alistair Popple wrote:
> GUP uses pXX_devmap() calls to see if it needs to a get a reference on
> the associated pgmap data structure to ensure the pages won't go
> away. However it's a driver responsibility to ensure that if pages are
> mapped (ie. discoverable by GUP) that they are not offlined or removed
> from the memmap so there is no need to hold a reference on the pgmap
> data structure to ensure this.
> 
> Furthermore mappings with PFN_DEV are no longer created, hence this
> effectively dead code anyway so can be removed.
> 
> Signed-off-by: Alistair Popple <apopple@...dia.com>
> ---
>  include/linux/huge_mm.h |   3 +-
>  mm/gup.c                | 162 +----------------------------------------
>  mm/huge_memory.c        |  40 +----------
>  3 files changed, 5 insertions(+), 200 deletions(-)

Hooray! Goodbye dev_pagemap mess in gup.c.

Reviewed-by: Dan Williams <dan.j.williams@...el.com>