[Haskell-cafe] Can't prevent memoizing in simple code
The buffer http://hpaste.org/68595 presents a simple code I tried to profile. I spotted what I strongly think to be an abusive memoization. The problem is that I don't see how to (simply) get rid of it. Compiled with -O2, it consumes 130MB of memory, however lines A and B executed separately consume each only 1MB. The infinite list (l 1), whatever I do, keeps being shared between lines A and B. I tried to wrap it in a function, as you can see, I also tried to make it explicitely polymorphic (bypassing monomorphic restriction), nothing solves it, GHC is just to good at memoizing. NB: When compiled without optimisations, the sharing does not happen (side note: but then lack of strictness analysis -- which is what I was testing at the first place -- makes line A (call to suminit2) consume a lot of memory, but this is normal). ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Can't prevent memoizing in simple code
On May 16, 2012, at 12:08 PM, Yves Parès wrote:
The buffer http://hpaste.org/68595 presents a simple code I tried to profile.
I spotted what I strongly think to be an abusive memoization. The problem is
that I don't see how to (simply) get rid of it.
Compiled with -O2, it consumes 130MB of memory, however lines A and B
executed separately consume each only 1MB.
The infinite list (l 1), whatever I do, keeps being shared between lines A
and B.
I tried to wrap it in a function, as you can see, I also tried to make it
explicitely polymorphic (bypassing monomorphic restriction), nothing solves
it, GHC is just to good at memoizing.
Adding a {-# NOINLINE l #-} annotation helps here. Syntactically, it must be
located somewhere a type signature for l would also be valid.
Anthony
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Re: [Haskell-cafe] Can't prevent memoizing in simple code
Thanks ^^
My other solution was a dirty trick:
Changing the second (l 1) by a (l (div 2 2)), which would only be good
until GHC knows how to statically analyse it (2-1 wasn't working for
instance).
I also noticed (while profiling to confirm that this was the source of the
memory leak) that adding manually cost centres forces the re-evaluation:
main = do
print $ suminit2 ({-# SCC list1 #-} l 1) 100 0
print $ fst $ suminit ({-# SCC list2 #-} l 1) 100 0
where
l n = enumFrom n
CAF:main5 Main 97 00.00.026.6
50.0
main Main118 00.00.026.6
50.0
list2Main119 00.00.026.6 *50.0
*
main.l Main120 1 26.6 50.026.6
50.0
[...]
CAF:main8 Main 95 00.00.030.4
50.0
main Main110 00.00.030.4
50.0
list1Main111 00.00.030.4
*50.0*
main.l Main112 1 30.4 50.030.4
50.0
We see here that allocations are shared between list1 and list2 (I expected
list1 to get 100% and list2 0%, due to sharing).
Strange...
2012/5/16 Anthony Cowley acow...@gmail.com
On May 16, 2012, at 12:08 PM, Yves Parès wrote:
The buffer http://hpaste.org/68595 presents a simple code I tried to
profile.
I spotted what I strongly think to be an abusive memoization. The problem
is that I don't see how to (simply) get rid of it.
Compiled with -O2, it consumes 130MB of memory, however lines A and B
executed separately consume each only 1MB.
The infinite list (l 1), whatever I do, keeps being shared between lines A
and B.
I tried to wrap it in a function, as you can see, I also tried to make it
explicitely polymorphic (bypassing monomorphic restriction), nothing solves
it, GHC is just to good at memoizing.
Adding a {-# NOINLINE l #-} annotation helps here. Syntactically, it must
be located somewhere a type signature for l would also be valid.
Anthony
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