Re: [RFC PATCH v1] tools/mm: Add thpmaps script to dump THP usage info

[John Hubbard <jhubbard@nvidia.com>]

On 1/9/24 19:51, Barry Song wrote:
> On Wed, Jan 10, 2024 at 11:35 AM John Hubbard <jhubbard@nvidia.com> wrote:
...
>> Hi Ryan,
>>
>> One thing that immediately came up during some recent testing of mTHP
>> on arm64: the pid requirement is sometimes a little awkward. I'm running
>> tests on a machine at a time for now, inside various containers and
>> such, and it would be nice if there were an easy way to get some numbers
>> for the mTHPs across the whole machine.
>>
>> I'm not sure if that changes anything about thpmaps here. Probably
>> this is fine as-is. But I wanted to give some initial reactions from
>> just some quick runs: the global state would be convenient.
> 
> +1. but this seems to be impossible by scanning pagemap?
> so may we add this statistics information in kernel just like
> /proc/meminfo or a separate /proc/mthp_info?
> 

Yes. From my perspective, it looks like the global stats are more useful
initially, and the more detailed per-pid or per-cgroup stats are the
next level of investigation. So feels odd to start with the more
detailed stats.

However, Ryan did clearly say, above, "In future we may wish to
introduce stats directly into the kernel (e.g. smaps or similar)". And
earlier he ran into some pushback on trying to set up /proc or /sys
values because this is still such an early feature.

I wonder if we could put the global stats in debugfs for now? That's
specifically supposed to be a "we promise *not* to keep this ABI stable"
location.


thanks,
-- 
John Hubbard
NVIDIA