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. Duncan