[Haskell-cafe] OS swapping and haskell data structures

Duncan Coutts duncan.coutts at worc.ox.ac.uk
Wed Aug 1 14:40:32 EDT 2007

On Wed, 2007-08-01 at 11:31 -0700, Bryan O'Sullivan wrote:
> Alex Jacobson wrote:
> > If you create a Data.Map or Data.Set larger than fits in physical 
> > memory, will OS level swapping enable your app to behave reasonably or 
> > will things just die catastrophically as you hit a memory limit?
> Relying on the OS to page portions of your app in and out should always 
> be the fallback of last resort.  You are fairly guaranteed to get 
> terrible performance because the VM subsystem can't anticipate your 
> app's memory access patterns, and catastrophic death of either your app 
> or other system processes is a strong possibility (Google for "OOM 
> killer" if you want some horror stories).  In many cases, you can't even 
> rely on paging being possible.

Furthermore, as I understand it, GC does not interact well with paging
since the GC has to traverse the data structures on major GCs it'll
force it all to be kept in memory.


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