Date: Wed, 14 Feb 2024 00:02:30 +0100
From: David Hildenbrand <david@...hat.com>
To: Suren Baghdasaryan <surenb@...gle.com>,
 Kent Overstreet <kent.overstreet@...ux.dev>
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Subject: Re: [PATCH v3 00/35] Memory allocation profiling

On 13.02.24 23:59, Suren Baghdasaryan wrote:
> On Tue, Feb 13, 2024 at 2:50 PM Kent Overstreet
> <kent.overstreet@...ux.dev> wrote:
>>
>> On Tue, Feb 13, 2024 at 11:48:41PM +0100, David Hildenbrand wrote:
>>> 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.
>>
>> He requested something?
> 
> Yes, a cleaner instrumentation. Unfortunately the cleanest one is not
> possible until the compiler feature is developed and deployed. And it
> still would require changes to the headers, so don't think it's worth
> delaying the feature for years.
> 

I was talking about this: "I can live with all the downsides of the 
proposed implementationas 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".

I certainly cannot be motivated at this point to review and ack this, 
unfortunately too much negative energy around here.

-- 
Cheers,

David / dhildenb

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