Ooh, great -- could you point me in the right direction for that? ________________________________________ From: Don Stewart [dons@galois.com] Sent: Wednesday, January 07, 2009 9:23 AM To: Bulat Ziganshin Cc: Bueno, Denis; haskell-cafe@haskell.org Subject: Re: [Haskell-cafe] Blitting one IOUArray into another You can of course memcpy unboxed arrays fairly easily. bulat.ziganshin:
Hello Denis,
Wednesday, January 7, 2009, 6:56:36 PM, you wrote:
memory allocated for i :)))
each new copy of i needs one word. the situation was much worse with Int64, of course :)
Hi all,
I'm seeing a lot of unexpected memory allocation with some simple code that copies the contents of one vector (IOUArray Int Int64) into another of the same type and dimensions. In particular, profiling reveals that `copyInto' is allocating oodles and oodles of memory.
My small test case creates two 50000-element arrays and performs 10000 copies from one into the other. Since the elements are Int64s and the arrays are unboxed, each array should be
50000 elements * 8 bytes per element = 400,000 bytes
and so the arrays should only take 800,000 bytes total. I understand there's some overhead for thunks and whatnot, but the profiler reported allocation is around 40 billion bytes. And almost all of that allocation is in my copying function, not in main (main allocates the arrays).
I've attached two versions of the code, just for comparison. The only difference is the way the copying is done. One calls `getBounds' to figure out the bounds, and one is given the bounds for copying. They're both about the same speed and allocation (originally I was using IOUArray Int64 Int64, and there was a much greater allocation difference between the two versions; but that went away. Oh well).
So, does anyone know why copying takes so much allocation? I expect there is _some_ way to just move memory from one array to another, like a memcpy -- how can I do that? Denis
-- Best regards, Bulat mailto:Bulat.Ziganshin@gmail.com
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