profile not showing it all?

Duncan Coutts duncan.coutts at
Fri Sep 9 12:38:14 EDT 2005

On Fri, 2005-09-09 at 19:54 +0400, Bulat Ziganshin wrote:
> Hello Duncan,
> Friday, September 09, 2005, 5:17:06 PM, you wrote:
> >> btw, i suggested to GHC team auto-switching to compacting algorithm
> >> when program begins swapping. you can vote for this suggestion if it
> >> what you need ;)
> DC> That's much easier said than done. Automatically picking an optimal heap
> DC> size for the current machine VM pressure is not so easy. Most OSs do not
> DC> give any advice to apps on how much memory they can sensibly make use of
> DC> or even tell you in any sensible manner when they are starting to
> DC> thrash.
> in windows it can be made, by example, simply by comparing value of
> available physical memory at moment of starting GC with size of heap.
> if availbale physical memory is smaller, then it have meaning to start
> compacting algorithm instead of copying. compacting algorithm runs
> about 2 times slower if there is enough memory, but when swapping
> occurs it will be many times faster, of course

It's a reasonable aproximation but it doesn't take into account any
other programs running on the machine at the same time. And there's also
the fact that VM pressure is rather dynamic in nature.


More information about the Glasgow-haskell-users mailing list