Date: Tue, 13 Feb 2024 23:48:41 +0100
From: David Hildenbrand <david@...hat.com>
To: Suren Baghdasaryan <surenb@...gle.com>
Cc: Kent Overstreet <kent.overstreet@...ux.dev>,
 Michal Hocko <mhocko@...e.com>, akpm@...ux-foundation.org, vbabka@...e.cz,
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Subject: Re: [PATCH v3 00/35] Memory allocation profiling

On 13.02.24 23:30, Suren Baghdasaryan wrote:
> On Tue, Feb 13, 2024 at 2:17 PM David Hildenbrand <david@...hat.com> wrote:
>>
>> On 13.02.24 23:09, Kent Overstreet wrote:
>>> On Tue, Feb 13, 2024 at 11:04:58PM +0100, David Hildenbrand wrote:
>>>> On 13.02.24 22:58, Suren Baghdasaryan wrote:
>>>>> On Tue, Feb 13, 2024 at 4:24 AM Michal Hocko <mhocko@...e.com> wrote:
>>>>>>
>>>>>> On Mon 12-02-24 13:38:46, Suren Baghdasaryan wrote:
>>>>>> [...]
>>>>>>> We're aiming to get this in the next merge window, for 6.9. The feedback
>>>>>>> we've gotten has been that even out of tree this patchset has already
>>>>>>> been useful, and there's a significant amount of other work gated on the
>>>>>>> code tagging functionality included in this patchset [2].
>>>>>>
>>>>>> I suspect it will not come as a surprise that I really dislike the
>>>>>> implementation proposed here. I will not repeat my arguments, I have
>>>>>> done so on several occasions already.
>>>>>>
>>>>>> Anyway, I didn't go as far as to nak it even though I _strongly_ believe
>>>>>> this debugging feature will add a maintenance overhead for a very long
>>>>>> time. I can live with all the downsides of the proposed implementation
>>>>>> _as long as_ there is a wider agreement from the MM community as this is
>>>>>> where the maintenance cost will be payed. So far I have not seen (m)any
>>>>>> acks by MM developers so aiming into the next merge window is more than
>>>>>> little rushed.
>>>>>
>>>>> We tried other previously proposed approaches and all have their
>>>>> downsides without making maintenance much easier. Your position is
>>>>> understandable and I think it's fair. Let's see if others see more
>>>>> benefit than cost here.
>>>>
>>>> Would it make sense to discuss that at LSF/MM once again, especially
>>>> covering why proposed alternatives did not work out? LSF/MM is not "too far"
>>>> away (May).
>>>>
>>>> I recall that the last LSF/MM session on this topic was a bit unfortunate
>>>> (IMHO not as productive as it could have been). Maybe we can finally reach a
>>>> consensus on this.
>>>
>>> I'd rather not delay for more bikeshedding. Before agreeing to LSF I'd
>>> need to see a serious proposl - what we had at the last LSF was people
>>> jumping in with half baked alternative proposals that very much hadn't
>>> been thought through, and I see no need to repeat that.
>>>
>>> Like I mentioned, there's other work gated on this patchset; if people
>>> want to hold this up for more discussion they better be putting forth
>>> something to discuss.
>>
>> I'm thinking of ways on how to achieve Michal's request: "as long as
>> there is a wider agreement from the MM community". If we can achieve
>> that without LSF, great! (a bi-weekly MM meeting might also be an option)
> 
> There will be a maintenance burden even with the cleanest proposed
> approach. 

Yes.

> We worked hard to make the patchset as clean as possible and
> if benefits still don't outweigh the maintenance cost then we should
> probably stop trying.

Indeed.

> At LSF/MM I would rather discuss functonal
> issues/requirements/improvements than alternative approaches to
> instrument allocators.
> I'm happy to arrange a separate meeting with MM folks if that would
> help to progress on the cost/benefit decision.
Note that I am only proposing ways forward.

If you think you can easily achieve what Michal requested without all 
that, good.

My past experience was that LSF/MM / bi-weekly MM meetings were 
extremely helpful to reach consensus.

-- 
Cheers,

David / dhildenb

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