More radical ideas about gc and reference counting

[via Digitalmars-d]

On Tuesday, 13 May 2014 at 06:12:46 UTC, Rainer Schuetze wrote:
>
>
> On 13.05.2014 00:15, Martin Nowak wrote:

>> There is a problem with this scheme, copy-on-write is extremely
>> expensive when a mutation happens. That's one page fault 
>> (context
>> switch) + copying a whole page + mapping the new page.
>
> I agree that this might be critical, but it is a one time cost 
> per page. It seems unrealistic to do this with user mode 
> exceptions, but the OS should have this optimized pretty well.

As I pointed out this won't help dynamic games that easily can 
touch 50000 pages per frame if you use a single global allocator. 
2000 cycles * 50K = 100K = frame drop. What's worse, if you are 
low on memory you will start to swap to disk (or compress pages).

So that means you have to optimize for collections, use dedicated 
allocators that keep dynamic data on the same pages etc... 
Basically you get the disadvantage of manual memory management 
and in the worst case the memory requirements of a copying GC 
without the benefits...