[gclist] Fragmentation terminology

Henry G. Baker hbaker@netcom.com
Thu, 15 May 1997 07:28:43 -0700 (PDT)

>  || From: Nick Barnes <nickb@harlequin.co.uk>
>  || Date: Wed, 14 May 1997 16:27:30 +0100
>  || Subject: [gclist] Fragmentation terminology
>  || 
>  || Fragmentation is when an allocator cannot satisfy a request [without
>  || going to the OS for more memory] despite there being sufficient unused
>  || space.
> Picking nits (since you are discussing terminology): in OS circles, we call
> fragmentation the fact that there are unused/unusable holes in the memory
> allocation.  So there are degrees of fragmentation; e.g. it makes sense to say
> "a bit of fragmentation doesn't hurt", "this disk is severely fragmented".
> Under your definition these sentences would not make sense.
>                                         Marc

Elsewhere, I have argued that 'fragmentation' is a thermodynamic
concept.  A heap whose free space is in a single block is very 'cold',
because the amount of information required to describe it is very
small.  If the amount of information required to describe the set of
free blocks is large, then the heap is 'hot'.

Henry Baker
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