More radical ideas about gc and reference counting

[Rainer Schuetze via Digitalmars-d]

On 13.05.2014 00:15, Martin Nowak wrote:
> On 05/11/2014 08:18 PM, Rainer Schuetze wrote:
>>
>> 1. Use a scheme that takes a snapshot of the heap, stack and registers
>> at the moment of collection and do the actual collection in another
>> thread/process while the application can continue to run. This is the
>> way Leandro Lucarellas concurrent GC works
>> (http://dconf.org/2013/talks/lucarella.html), but it relies on "fork"
>> that doesn't exist on every OS/architecture. A manual copy of the memory
>> won't scale to very large memory, though it might be compressed to
>> possible pointers. Worst case it will need twice as much memory as the
>> current heap.
>
> 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.

 > It's much worse
 > with huge pages (2MB page size).

How common are huge pages nowadays?