[GHC] #13288: Resident set size exceeds +RTS -M limit with large nurseries

[GHC]

#13288: Resident set size exceeds +RTS -M limit with large nurseries
-------------------------------------+-------------------------------------
        Reporter:  j6carey           |                Owner:  (none)
            Type:  bug               |               Status:  patch
        Priority:  normal            |            Milestone:  8.2.1
       Component:  Runtime System    |              Version:  8.0.2
      Resolution:                    |             Keywords:
Operating System:  Linux             |         Architecture:  x86_64
 Type of failure:  Runtime           |  (amd64)
  performance bug                    |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):  Phab:D3143
       Wiki Page:                    |
-------------------------------------+-------------------------------------

Comment (by j6carey):

 Thank you for committing this fix.

 We still see RSS growth beyond the -M limit, but that is due to having a
 large number of partially-used megablocks involved in the free block group
 list.  They cannot be returned to the operating system because they are
 still partly in use, and yet their free space is not counted as heap size,
 and therefore is not limited by -M.  We have not yet figured out why there
 is such high fragmentation in our application.  But clearly that is a
 distinct issue.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13288#comment:5>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler