On 16/06/2010 14:04, Jesper Louis Andersen wrote:
Finally, you can tune the eden/nursery generation by providing +RTS -A5m for instance. The default is 0.5 megabytes which I think is way too low for most work. Increasing it blindly will hurt though as you will hit L1/L2 cache limits and get worse performance.
Not sure I follow here - you say that 0.5MB is too low, and yet increasing it will hurt performance (I agree with you on the last point: in my experience most of the time increasing it does tend to make things worse). OTOH there are programs where the 0.5MB default really hurts - the binary-trees benchmark on the shootout, for example. If we could identify a useful set of heuristics to decide when it's a good idea to increase the nursery size, that would help. I think the only way to get a real handle on this is to put together a comprehensive benchmark suite and test lots of different programs with different heap requirements, and on lots of different machines with different cache sizes. Incedentally, GHC HEAD has a new flag +RTS -H, which increases the nursery size but without increasing the overall memory use (basically it uses the space left over after a copying major collection for the nursery). This sometimes helps with programs that have large heaps, but not always. Cheers, Simon
My application has had problems with both retainer profiling and (especially) biographical profiling - but whenever I try to make a watered-down reproducible example the problem disappears. If you do manage the get a reproducible bug going, I am interested in that ticket.
So, the main question:
I have a program that runs some computation in a monad stack before extracting the final result, a list, and passing it on. When run under the heap profiler, there's a huge spike in that phase, which I think should be mostly bogus usage, since the final output is so relatively small. When I run under -hb I see big bands for LAG and DRAG.
I would look at retainers. Or if you hold on to things you don't use anymore rather than dropping the reference. In general, the heap profiler is the way to go for removing space leak problems -