[GHC] #10812: High memory usage

[GHC]

#10812: High memory usage
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        Reporter:  danilo2       |                   Owner:
            Type:  bug           |                  Status:  new
        Priority:  high          |               Milestone:
       Component:  Compiler      |                 Version:  7.10.2
      Resolution:                |                Keywords:
Operating System:  MacOS X       |            Architecture:  x86_64 (amd64)
 Type of failure:  None/Unknown  |               Test Case:
      Blocked By:                |                Blocking:
 Related Tickets:                |  Differential Revisions:
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Comment (by bgamari):

 The problem is that the GC isn't being performed after traversing `xr`; if
 you manually insert a `performGc` before the `threadDelay` then you will
 find things behave as you expect.

 For the record, the given test seems to behave as expected on my machine.

 My testing methodology was rather crude,
 {{{
 $ ghc -O Test.hs; ./Test & pid=$!; while true; do cat /proc/$pid/stat >>
 stat; sleep 0.01; done
 $ ipython --pylab
 >>> a = genfromtxt('stat')
 >>> vsize = a[:,22] # see proc(5)
 >>> plot(vsize / 1024**2)
 >>> ylabel('vsize / megabytes')
 >>> xlabel('something approximating time')
 }}}

 With `[1..10000000]` `vsize` peaked around 1.8GB around 3 seconds after
 starting the process. With the testcase provided above `vsize` remained at
 this peak for the remaining duration of the program. With a manual
 `performGC` after the traversal, however, it dropped to essentially zero
 around a second after plateauing. It stayed there for the rest of the
 execution.

 The moral of the story is if you want the runtime to GC at a given point,
 you must tell it. GC occurs due to allocation. Given that there is
 essentially no allocation after the traversal it isn't terribly surprising
 that no GC is occurring.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10812#comment:3>
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