Do you use D's GC?

[Gregor Mückl]

On Tuesday, 3 August 2021 at 14:34:19 UTC, Steven Schveighoffer 
wrote:
> On 8/3/21 5:15 AM, Gregor Mückl wrote:
>> The D garbage collector seems reasonable for applications with 
>> small (object sized) allocations. But that changes when you 
>> allocate large blocks of memory: due to a bug internal to the 
>> tracking of allocated pages, performance gradually degrades 
>> over time. So if you have to allocate large(ish) buffers 
>> regularly, it'll show over time. I reported that bug here with 
>> a repro case, but it didn't get any attention yet:
>> 
>> https://issues.dlang.org/show_bug.cgi?id=20434
>> 
>> I haven't managed to understand thag part of the GC enough to 
>> submit a patch myself :(.
>
> Is that repro case doing what you think it is doing? It appears 
> to keep adding more and more larger allocations to the mix.
>
> It seems you are calculating a `size` variable and never using 
> it.
>
> I think possibly you meant to use `size * 1024 * 1024` instead 
> of `i * 1024 * 1024`.
>
> In regards to the conservative nature of the GC, the larger the 
> blocks get, the more chances they get "accidentally" pointed at 
> by the stack (or some other culprit). 64-bit memory space 
> should alleviate a lot of this, but I think there are still 
> cases where it can pin data unintentionally.
>
> -Steve

I apologize for not replying earlier. I was very busy with real 
life stuff since I posted this.

Also, I feel REALLY embarrassed. You are right. I am sorry for 
wasting time with this. I was 100% certain that my code was right 
when I opened the bug report and I am sure that I checked it 
multiple times. But going back to the example program I have 
locally, it clearly contains this stupid bug.

I fixed the allocation size as you said and now I can't reproduce 
the behavior I remember. I've checked several dmd builds between 
2.088 and 2.096 again and it doesn't show.

So the GC is just fine after all - and I've made an idiot of 
myself. Again.