[GHC] #6104: Regression: space leak in HEAD vs. 7.4

[GHC]

#6104: Regression: space leak in HEAD vs. 7.4
---------------------------------+------------------------------------------
    Reporter:  simonmar          |       Owner:                              
        Type:  bug               |      Status:  new                         
    Priority:  highest           |   Milestone:  7.6.1                       
   Component:  Compiler          |     Version:  7.5                         
    Keywords:                    |          Os:  Unknown/Multiple            
Architecture:  Unknown/Multiple  |     Failure:  Compile-time performance bug
  Difficulty:  Unknown           |    Testcase:                              
   Blockedby:                    |    Blocking:                              
     Related:                    |  
---------------------------------+------------------------------------------
 I often keep an eye on compiler performance by compiling Cabal.  Yesterday
 I noticed that HEAD appears to have a space leak: it needs 806MB to
 compile Cabal with -O, vs 424MB with 7.4.1.

 Here are the results.  First 7.4.1:

 {{{
 $ ghc-7.4.1 -O --make Distribution.Simple +RTS -s
 }}}

 {{{
   53,658,077,704 bytes allocated in the heap
    9,679,170,192 bytes copied during GC
      148,845,896 bytes maximum residency (56 sample(s))
        6,610,216 bytes maximum slop
              424 MB total memory in use (0 MB lost due to fragmentation)

                                     Tot time (elapsed)  Avg pause  Max
 pause
   Gen  0     102382 colls,     0 par   24.24s   24.22s     0.0002s
 0.0046s
   Gen  1        56 colls,     0 par   12.48s   12.48s     0.2229s
 0.4738s

   INIT    time    0.00s  (  0.00s elapsed)
   MUT     time   57.37s  ( 60.81s elapsed)
   GC      time   36.72s  ( 36.70s elapsed)
   EXIT    time    0.00s  (  0.00s elapsed)
   Total   time   94.09s  ( 97.52s elapsed)
 }}}

 And HEAD:

 {{{
 $ ghc-nightly2 -O --make Distribution.Simple +RTS -s
 }}}

 {{{
   55,699,304,032 bytes allocated in the heap
   11,721,558,728 bytes copied during GC
      288,988,200 bytes maximum residency (50 sample(s))
        7,808,192 bytes maximum slop
              806 MB total memory in use (0 MB lost due to fragmentation)

                                     Tot time (elapsed)  Avg pause  Max
 pause
   Gen  0     107655 colls,     0 par   28.83s   28.83s     0.0003s
 0.0043s
   Gen  1        50 colls,     0 par   16.36s   16.36s     0.3272s
 1.0063s

   TASKS: 3 (1 bound, 2 peak workers (2 total), using -N1)

   INIT    time    0.00s  (  0.00s elapsed)
   MUT     time   59.87s  ( 63.18s elapsed)
   GC      time   45.19s  ( 45.19s elapsed)
   EXIT    time    0.00s  (  0.00s elapsed)
   Total   time  105.07s  (108.37s elapsed)
 }}}

 We need to squash this before 7.6 is released.

-- 
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/6104>
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