Memory allocation in D

[Marius Muja]

Sean Kelly wrote:

> For what it's worth, my concern with the current behavior is that its 
> worst-case scenario coincides with typical usage.  It is extremely 
> common for a programmer to use array sizes that are powers of two, and 
> this is the situation which results in the maximum unused space per 
> block (because the runtime adds 1 to the size of all array allocations 
> passed to the GC).  Totally stinks, and I'm running out of ideas.  I 
> don't suppose someone can offer a suggestion for how to address this, 
> other than "just always allocate exactly what they request and if they 
> get a page fault then too bad for them?"

That was my problem also. I was using array sizes that were powers of 
two and because of the extra 1 there were many memory pages wasted. For 
example in one of my tests I was allocating float arrays of size 1024 
(4096 bytes) which were taking 2 pages instead of 1 because of the extra 
1 added, and that's where I was observing that with D's new operator I 
can only allocate half as much memory than with malloc.
Oddly the same problem occurs if I allocate much larger arrays of 
exactly 1024*1024 floats (4MB size). Seems that instead of 4MB, D's 
runtime allocated 8MB for each of these arrays. Is D's runtime using 4MB 
pages for large memory allocations?


Marius