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

Barry Song
2024-01-10T09:09:26Z

On Wed, Jan 10, 2024 at 4:58 PM Ryan Roberts <ryan.roberts@arm.com> wrote:
>
> On 10/01/2024 08:02, Barry Song wrote:
> > On Wed, Jan 10, 2024 at 12:16 PM John Hubbard <jhubbard@nvidia.com> wrote:
> >>
> >> 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.
>
> Just to confirm, you're expecting these "global" stats be truely global and not
> per-container? (asking because you exploicitly mentioned being in a container).
> If you want per-container, then you can probably just create the container in a
> cgroup?
>
> >>>>
> >>>> 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.
>
> Thanks for taking this for a spin! Appreciate the feedback.
>
> >>>
> >>> +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.
> >>
> >
> > probably because this can be done without the modification of the kernel.
>
> Yes indeed, as John said in an earlier thread, my previous attempts to add stats
> directly in the kernel got pushback; DavidH was concerned that we don't really
> know exectly how to account mTHPs yet
> (whole/partial/aligned/unaligned/per-size/etc) so didn't want to end up adding
> the wrong ABI and having to maintain it forever. There has also been some
> pushback regarding adding more values to multi-value files in sysfs, so David
> was suggesting coming up with a whole new scheme at some point (I know
> /proc/meminfo isn't sysfs, but the equivalent files for NUMA nodes and cgroups
> do live in sysfs).
>
> Anyway, this script was my attempt to 1) provide a short term solution to the
> "we need some stats" request and 2) provide a context in which to explore what
> the right stats are - this script can evolve without the ABI problem.
>
> > The detailed per-pid or per-cgroup is still quite useful to my case in which
> > we set mTHP enabled/disabled and allowed sizes according to vma types,
> > eg. libc_malloc, java heaps etc.
> >
> > Different vma types can have different anon_name. So I can use the detailed
> > info to find out if specific VMAs have gotten mTHP properly and how many
> > they have gotten.
> >
> >> 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.
>
> Now that I think about it, I wonder if we can add a --global mode to the script
> (or just infer global when neither --pid nor --cgroup are provided). I think I
> should be able to determine all the physical memory ranges from /proc/iomem,
> then grab all the info we need from /proc/kpageflags. We should then be able to
> process it all in much the same way as for --pid/--cgroup and provide the same
> stats, but it will apply globally. What do you think?

for debug purposes, it should be good. imaging there is a health
monitor which needs
to sample the stats of large folios online and periodically, this
might be too expensive.

>
> If we can possibly avoid sysfs/debugfs I would prefer to keep it all in a script
> for now.
>
> >
> > +1.
> >
> >>
> >>
> >> thanks,
> >> --
> >> John Hubbard
> >> NVIDIA
> >>
> >

Thanks
Barry