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

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Date:   Mon, 11 Nov 2019 08:00:12 +0000
From:   Toshiki Fukasawa <t-fukasawa@...jp.nec.com>
To:     Michal Hocko <mhocko@...nel.org>,
        "dan.j.williams@...el.com" <dan.j.williams@...el.com>
CC:     "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "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 2019/11/08 18:18, Michal Hocko wrote:
> 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?

We are writing a test program for hwpoison, which is a use case.
Without this patch, we can't see the HWPOISON flag on the
ZONE_DEVICE page.

Thanks,
Toshiki Fukasawa