Add fragmentation statistics to GHC.Stats
Motivation
Fragmentation is a key statistic when using the non-moving garbage collector. The event log has information about heap fragmentation, but it would be helpful to have the same information available from GHC.Stats
.
As far as I understand we can already get at this statistic by taking gcdetails_mem_in_use_bytes - gcdetails_live_bytes
. But I'm not sure that's right. And even if that's true, I think it would be more user friendly to make this stat available in an explicit way.
Proposal
Add a field to GHC.Stats.GCDetails
called gcdetails_fragmentation_bytes
that gives the same stats as the event log fragmentation counter.
I'm happy to implement this.