[GHC] #5259: Heap used by compacting collector larger than heap used without.

[GHC]

#5259: Heap used by compacting collector larger than heap used without.
-----------------------+----------------------------------------------------
    Reporter:  r6      |       Owner:                
        Type:  bug     |      Status:  new           
    Priority:  normal  |   Component:  Runtime System
     Version:  6.12.3  |    Keywords:                
    Testcase:          |   Blockedby:                
          Os:  Linux   |    Blocking:                
Architecture:  x86     |     Failure:  None/Unknown  
-----------------------+----------------------------------------------------

Comment(by r6):

 Here is a small example program:

 {{{
 module Main where

 import qualified Data.ByteString as BS

 l = map (BS.replicate (1024^2 `div` 2)) [0..]

 main = do
   print (map BS.head l)
   print (map BS.head l)
 }}}

 For me, ghc --make -O2 Alloc.hs && ./Alloc +RTS -M100M -c -S
 runs until the heap is exhasted and outputs:
 {{{
 Heap exhausted;
 Current maximum heap size is 104857600 bytes (100 MB);

       104,220,800 bytes allocated in the heap
              198 MB total memory in use (98 MB lost due to fragmentation)
 }}}
 On the other hand, ghc --make -O2 Alloc.hs && ./Alloc +RTS -M100M -S
 runs until the heap is exhasted and outputs:
 {{{
 Heap exhausted;
 Current maximum heap size is 104857600 bytes (100 MB);
       52,397,636 bytes allocated in the heap
              100 MB total memory in use (49 MB lost due to fragmentation)
 }}}

-- 
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/5259#comment:1>
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