Sounds similar to the bug we had in 6.12.1. It was a simple accounting bug, i.e., the GC was not invoked, because it didn't know that the memory was allocated.
On 20 April 2013 22:03, Edward Z. Yang <ezy...@mit.edu> wrote: > I don't seem to get the leak on latest GHC head. Running the program > in GC debug mode in 7.6.2 is quite telling; the program is allocating > *a lot* of megablocks. We probably fixed it though? > > Edward > > Excerpts from Mikhail Glushenkov's message of Sat Apr 20 01:55:10 -0700 2013: >> Hi all, >> >> This came up on StackOverflow [1]. When compiled with GHC (7.4.2 & >> 7.6.2), this simple program: >> >> main = print $ ack 4 1 >> where ack :: Int -> Int -> Int >> ack 0 n = n+1 >> ack m 0 = ack (m-1) 1 >> ack m n = ack (m-1) (ack m (n-1)) >> >> consumes all available memory on my machine and slows down to a crawl. >> However, when compiled with JHC it runs in constant space and is about >> as fast as the straightforward Ocaml version (see the SO question for >> benchmark numbers). >> >> I was able to fix the space leak by using CPS-conversion, but the >> CPS-converted version is still about 10 times slower than the naive >> version compiled with JHC. >> >> I looked both at the Core and Cmm, but couldn't find anything >> obviously wrong with the generated code - 'ack' is compiled to a >> simple loop of type 'Int# -> Int# -> Int#'. What's more frustrating is >> that running the program with +RTS -hc makes the space leak >> mysteriously vanish. >> >> Can someone please explain where the space leak comes from and if it's >> possible to further improve the runtime of this program with GHC? >> Apparently it's somehow connected to the stack management strategy, >> since running the program with a larger stack chunk size (+RTS -kc1M) >> makes the space leak go away. Interestingly, choosing smaller stack >> chunk sizes (256K, 512K) causes it to die with an OOM exception: >> >> $ time ./Test +RTS -kc256K >> Test: out of memory (requested 2097152 bytes) >> >> >> [1] >> http://stackoverflow.com/questions/16115815/ackermann-very-inefficient-with-haskell-ghc/16116074#16116074 >> > > _______________________________________________ > Glasgow-haskell-users mailing list > Glasgow-haskell-users@haskell.org > http://www.haskell.org/mailman/listinfo/glasgow-haskell-users _______________________________________________ Glasgow-haskell-users mailing list Glasgow-haskell-users@haskell.org http://www.haskell.org/mailman/listinfo/glasgow-haskell-users
