Re: [LSF/MM/BPF TOPIC] Multi-sized THP performance benchmarks and analysis on ARM64

[David Hildenbrand <david@redhat.com>]

On 09.04.24 20:41, Yang Shi wrote:
> On Thu, Apr 4, 2024 at 12:34 PM David Hildenbrand <david@redhat.com> wrote:
>>
>> On 04.04.24 20:57, Christoph Lameter (Ampere) wrote:
>>> On Mon, 1 Apr 2024, Jonathan Cameron wrote:
>>>
>>>> Sounds like useful data, but is it a suitable topic for LSF-MM?
>>>> What open questions etc is it raising?
>>>
>>>
>>> mTHP is new functionality that will require additional work to support
>>> more use cases. It is also unclear at this point in what usecases mTHP is
>>> useful and where no benefit can so far be seen. Also the effect of
>>> coalescing multiple PTE entries into one TLB entry is new to MM
>>> (CONT_PTE).
>>>
>>> Ultimately it would be useful to have mTHP support also provide larger
>>> blocksize capabilities for filesystem etc etc. mTHP needs to mature and an
>>> analysis of the arguable a bit experimental state of affairs can help a
>>> lot in getting there.
>>
>> Right, something like that (open items, missed use cases, requirements,
>> ideas, etc,.) would be a better (good!) fit.
>>
>> Pure benchmark results, analysis and recommendations are great. But
>> likely a better fit for a (white) paper, blog post,
>> less-discussion-focused conference.
> 
> Thanks for the suggestion. I didn't plan to enumerate any open items
> because I think those items (for example, khugepaged support, swap,
> etc) were already well-known by mm community and we have made some
> progress on some items.

I think there are two types of open items: "we obviously know what we 
have to do -- basic swap, khugepaged, etc. support" and "we don't really 
know what to do because it's rather an optimization problem and there 
might not be a right or wrong".

> 
> The potential future optimization choices led by the benchmark and
> analysis may be worth discussing. For example, shall the allocation
> fallback should try every single order, is it a good idea to let users
> decide the orders, etc. We didn't know what the good choice should be
> before we had some benchmark data.

Focusing on such open questions makes a lot of sense. Then, you can use 
the benchmark data to guide the discussion and share your insights :)

-- 
Cheers,

David / dhildenb