linux-kernel - Re: [PATCH 0/3] make pfn walker support ZONE

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Date:   Fri, 8 Nov 2019 10:18:51 +0100
From:   Michal Hocko <mhocko@...nel.org>
To:     Toshiki Fukasawa <t-fukasawa@...jp.nec.com>
Cc:     "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "dan.j.williams@...el.com" <dan.j.williams@...el.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
        "adobriyan@...il.com" <adobriyan@...il.com>,
        "hch@....de" <hch@....de>,
        "longman@...hat.com" <longman@...hat.com>,
        "sfr@...b.auug.org.au" <sfr@...b.auug.org.au>,
        "mst@...hat.com" <mst@...hat.com>, "cai@....pw" <cai@....pw>,
        Naoya Horiguchi <n-horiguchi@...jp.nec.com>,
        Junichi Nomura <j-nomura@...jp.nec.com>
Subject: Re: [PATCH 0/3] make pfn walker support ZONE_DEVICE

On Fri 08-11-19 00:08:03, Toshiki Fukasawa wrote:
> This patch set tries to make pfn walker support ZONE_DEVICE.
> This idea is from the TODO in below patch:
> 
>   commit aad5f69bc161af489dbb5934868bd347282f0764
>   Author: David Hildenbrand <david@...hat.com>
>   Date:   Fri Oct 18 20:19:20 2019 -0700
> 
> 	fs/proc/page.c: don't access uninitialized memmaps in fs/proc/page.c
> 
> pfn walker's ZONE_DEVICE support requires capability to identify
> that a memmap has been initialized. The uninitialized cases are 
> as follows:
> 
> 	a) pages reserved for ZONE_DEVICE driver
> 	b) pages currently initializing
> 
> This patch set solves both of them.

Why do we want this? What is the usecase?

> 
> Toshiki Fukasawa (3):
>   procfs: refactor kpage_*_read() in fs/proc/page.c
>   mm: Introduce subsection_dev_map
>   mm: make pfn walker support ZONE_DEVICE
> 
>  fs/proc/page.c           | 155 ++++++++++++++++++++---------------------------
>  include/linux/memremap.h |   6 ++
>  include/linux/mmzone.h   |  19 ++++++
>  mm/memremap.c            |  31 ++++++++++
>  mm/sparse.c              |  32 ++++++++++
>  5 files changed, 154 insertions(+), 89 deletions(-)
> 
> -- 
> 1.8.3.1
> 

-- 
Michal Hocko
SUSE Labs