On 14 April 2005 15:35, Josef Svenningsson wrote:
I've had some fun chasing around a couple of space leaks lately. One of the graphs that I produced looked like this: www.cs.chalmers.se/~josefs/coresa.ps
Notice the shape of the graph. It shows a perfect squareroot function. But my program should be allocating at a constant rate. From previous experience this suggests that there is a time complexity bug in the garbage collector. This makes it take time proportional to the square of the amount of allocated memory. Can someone confirm this?
The X axis of the heap profile is mutator time: that is runtime excluding GC time, so you wouldn't see any non-linear GC effects in the shape of the heap profile anyway. You'll be able to confirm this by comparing the time on the profile to the wall-clock time, and checking the output from +RTS -sstderr is useful too. It's possible you're seeing cache effects: as the working set grows larger, the program slows down. The shape does look a bit too perfect to be cache effects, though. I wouldn't rule out any bugs (of course :-), so please send us further evidence if you find it. Cheers, Simon