Re: [PATCH 2/2] Add /proc/PID/{smaps, numa_maps} support for DAX

[Dan Williams]

On Thu, Oct 26, 2017 at 9:00 PM, Du, Fan <fan.du@xxxxxxxxx> wrote:
>
>
>>-----Original Message-----
>>From: linux-kernel-owner@xxxxxxxxxxxxxxx
>>[mailto:linux-kernel-owner@xxxxxxxxxxxxxxx] On Behalf Of Dave Hansen
>>Sent: Thursday, October 26, 2017 10:51 PM
>>To: Michal Hocko <mhocko@xxxxxxxxxx>
>>Cc: Du, Fan <fan.du@xxxxxxxxx>; akpm@xxxxxxxxxxxxxxxxxxxx; hch@xxxxxx;
>>Williams, Dan J <dan.j.williams@xxxxxxxxx>; linux-kernel@xxxxxxxxxxxxxxx;
>>linux-api@xxxxxxxxxxxxxxx
>>Subject: Re: [PATCH 2/2] Add /proc/PID/{smaps, numa_maps} support for DAX
>>
>>On 10/26/2017 07:31 AM, Michal Hocko wrote:
>>> On Thu 26-10-17 07:24:14, Dave Hansen wrote:
>>>> Actually, I don't remember whether it was tooling or just confused
>>>> humans.  I *think* Dan was trying to write test cases for huge page DAX
>>>> support and couldn't figure out whether or not it was using large pages.
>>>
>>> That sounds like a very weak justification to adding new stuff to smaps
>>> to be honest.
>>
>>Yep, agreed.  It can't go in _just_ for DAX, and Fan and the other DAX
>>folks need to elaborate on their needs here.
>
> If user creates device DAX /dev/dax with some capacity like 512G, mmap it and
> Use it will, or touched 128G. To my best knowledge at this part, there is no
> statistics reported how much memory behind DAX actually used.
>
> This is the problem our customer is facing right now.

I'm not sure I understand, DAX is statically allocated. There's no
private memory taken from the page allocator to back device-dax
mappings. Unless you are trying to determine memory usage of page
tables?