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

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Message-ID: <4367f507-97ba-a74e-6bf5-811cdd6ecdf9@redhat.com>
Date:   Wed, 28 Aug 2019 10:18:41 -0400
From:   Waiman Long <longman@...hat.com>
To:     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-fsdevel@...r.kernel.org,
        linux-mm@...ck.org, Stephen Rothwell <sfr@...b.auug.org.au>,
        "Michael S. Tsirkin" <mst@...hat.com>,
        Toshiki Fukasawa <t-fukasawa@...jp.nec.com>
Subject: Re: [PATCH v2] fs/proc/page: Skip uninitialized page when iterating
 page structures

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