[GHC] #11603: Fix/clarify documentation in GHC.Stats

[GHC]

#11603: Fix/clarify documentation in GHC.Stats
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           Reporter:  dcturner       |             Owner:
               Type:  task           |            Status:  new
           Priority:  normal         |         Milestone:
          Component:  Core           |           Version:  8.1
  Libraries                          |
           Keywords:                 |  Operating System:  Unknown/Multiple
       Architecture:                 |   Type of failure:  Documentation
  Unknown/Multiple                   |  bug
          Test Case:                 |        Blocked By:
           Blocking:                 |   Related Tickets:
Differential Rev(s):                 |         Wiki Page:
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 The following were not clear to me until I read the source:

 `numByteUsageSamples` is (also) the number of major GCs performed.

 `currentBytesUsed` is the number of live bytes ''at the end of the last
 major GC''.

 Is `currentBytesSlop` also at the end of the last major GC? Can't see that
 it's actually set to anything nonzero anywhere...

 The comments for `cumulativeBytesUsed` and `parTotBytesCopied` are in the
 wrong places.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11603>
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