GC statistics

[dsimcha]

On Wednesday, 10 October 2012 at 19:35:33 UTC, Andrei 
Alexandrescu wrote:
> This is mostly for GC experts out there - what statistics are 
> needed and useful, yet not too expensive to collect?
>
> https://github.com/D-Programming-Language/druntime/pull/236
>
>
> Andrei

I'd like to see mark, sweep and page-freeing time be counted 
separately so that if overall GC performance is slow, the user 
can identify where the bottleneck is.  For example, mark time 
will be slow if there's a lot of total memory to be scanned.  
Sweep time will be slow if there are a lot of blocks allocated, 
even if they're all small.  I'm not sure if this is feasible, 
though, because it assumes that the GC implementation is 
mark-sweep.  I guess we could name the subcategories something 
more generic like mark and process marks.