[Haskell-cafe] regression in memory usage between 6.10 and 7.x?

[Ben Franksen]

Am 17.12.2016 um 22:45 schrieb Sergey Vinokurov:
> After trying out different heap profiling modes it seems to me that
> the problem is caused by the lazy empty and final fields (attached as
> reg.svg). These fields contain thunks which hold references to regexps
> and this quickly fills out the heap. However, making fields strict
> improves the memory usage a lot, from 1030 MB to 61 MB:

Many thanks Sergey, that's it! Two exclamation marks added and all is well.

ben at sarun[1]: .../play/regexfp > ./re 500 +RTS -s
True
      96,115,528 bytes allocated in the heap
      20,225,160 bytes copied during GC
         154,376 bytes maximum residency (2 sample(s))
          37,368 bytes maximum slop
               1 MB total memory in use (0 MB lost due to fragmentation)
...
  Total   time    0.061s  (  0.059s elapsed)

Exactly as claimed in the paper.

I wonder why the authors did not mention that these fields should be
strict and how to (easily) achieve that (not even in a footnote).
Neither did the reviewers catch this omission.

Cheers
Ben

> On Sat, Dec 17, 2016 at 10:51 PM, Ben Franksen <ben.franksen at online.de> wrote:
>> In the functional pearl "A Play on Regular Expressions" by Sebastian
>> Fischer, Frank Huch, and Thomas Wilke, the authors explain how to
>> implement a Glushkov automaton in a very elegant way. They claim that
>> when they compile their code with ghc-6.10.4 and with -O2 optimization
>> they get:
>>
>> """
>> 1 MB total memory in use
>> ...
>> Total time 0.06s (0.21s elapsed)
>> """
>>
>> for a program that matches stdin against the equivalent (in grep -E
>> syntax) of
>>
>>  ^(a?){500}a{500}$
>>
>> When I try their code on my machine with ghc-7.10.3 (and also -O2) I get:
>>
>> """
>> ben at sarun[1]: .../play/regexfp > ghc Reg.hs -O2 -o re
>> [1 of 1] Compiling Main             ( Reg.hs, Reg.o )
>> Linking re ...
>> ben at sarun[1]: .../play/regexfp > ./re 500 +RTS -s
>> True
>> ...
>> 155 MB total memory in use
>> ...
>> Total   time    1.031s  (  1.037s elapsed)
>> """
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