Minimize GC memory footprint

[rikki cattermole]

On 07/02/2021 12:38 AM, Siemargl wrote:
> On Saturday, 6 February 2021 at 11:20:18 UTC, Imperatorn wrote:
>> On Saturday, 6 February 2021 at 09:42:38 UTC, rikki cattermole wrote:
>>> On 06/02/2021 3:32 PM, frame wrote:
>>>>  [...]
>>>
>>> This won't do anything.
>>>
>>>>  [...]
>>>
>>> Don't forget to stdout.flush; Otherwise stuff can get caught in the 
>>> buffer before erroring out.
>>>
>>>> [...]
>>>
>>> Turn on the precise GC, 32bit is a bit too small of a range and you 
>>> can get false positives like in this case (at least looks like it).
>>
>> For reference, how does one turn on precise GC?
> 
> https://dlang.org/spec/garbage.html#gc_config
> 
> Strange things happens:
> - precise scanning dont change result - OOM @ same round 27

Okay, its still seeing something is alive then.

> --DRT-gcopt=help  wont show used  gc implementation, also cleanup type 
> not printed

https://github.com/dlang/druntime/blob/master/src/core/gc/config.d#L36

> - maxPoolSize:N  dont limit total size of GC

Shouldn't change anything, except make OOM happen faster.

> - in gc:manual mode GC.collect() not releasing memory

https://github.com/dlang/druntime/blob/master/src/gc/impl/manual/gc.d#L84

> 
> When i print free GC memory, it seems to memory leaking
> writefln("Usage: %.2f MiB (free %.2f MiB) / collected: %d",
>      (cast(double) GC.stats.usedSize) / 1_048_576,
>      (cast(double) GC.stats.freeSize) / 1_048_576, 
> GC.profileStats.numCollections);
> stdout.flush();

I've compiled and ran it under ldc. Dmd in 32bit mode is certainly doing 
something that the GC doesn't appreciate. I can reproduce it with 
-m32mscoff as well. So yeah dmd specific all right.