linux-kernel - Re: [PATCH v2] fs/proc/page: Skip uninitialized page when iterating page structures

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Message-ID: <9a1395bc-d568-c4d7-2dde-7dde7b48ac0b@vx.jp.nec.com>
Date:   Thu, 29 Aug 2019 01:47:13 +0000
From:   Toshiki Fukasawa <t-fukasawa@...jp.nec.com>
To:     Waiman Long <longman@...hat.com>, Michal Hocko <mhocko@...nel.org>
CC:     Dan Williams <dan.j.williams@...il.com>,
        Alexey Dobriyan <adobriyan@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        Stephen Rothwell <sfr@...b.auug.org.au>,
        "Michael S. Tsirkin" <mst@...hat.com>,
        Junichi Nomura <j-nomura@...jp.nec.com>,
        Toshiki Fukasawa <t-fukasawa@...jp.nec.com>
Subject: Re: [PATCH v2] fs/proc/page: Skip uninitialized page when iterating
 page structures

On 2019/08/28 23:18, Waiman Long wrote:
> On 8/28/19 10:09 AM, Michal Hocko wrote:
>> On Wed 28-08-19 09:46:21, Waiman Long wrote:
>>> On 8/28/19 4:00 AM, Michal Hocko wrote:
>>>> On Tue 27-08-19 16:22:38, Michal Hocko wrote:
>>>>> Dan, isn't this something we have discussed recently?
>>>> This was http://lkml.kernel.org/r/20190725023100.31141-3-t-fukasawa@vx.jp.nec.com
>>>> and talked about /proc/kpageflags but this is essentially the same thing
>>>> AFAIU. I hope we get a consistent solution for both issues.
>>>>
>>> Yes, it is the same problem. The uninitialized page structure problem
>>> affects all the 3 /proc/kpage{cgroup,count,flags) files.
>>>
>>> Toshiki's patch seems to fix it just for /proc/kpageflags, though.
>> Yup. I was arguing that whacking a mole kinda fix is far from good. Dan
>> had some arguments on why initializing those struct pages is a problem.
>> The discussion had a half open end though. I hoped that Dan would try
>> out the initialization side but I migh have misunderstood.
> 
> If the page structures of the reserved PFNs are always initialized, that
> will fix the problem too. I am not familiar with the zone device code.
> So I didn't attempt to do that.
> 
> Cheers,
> Longman
> 
> 
I also think that the struct pages should be initialized.
I'm preparing to post the patch.

Toshiki Fukasawa