On Tue, 19 Apr 2011 18:34:33 +0400, dsimcha <[email protected]> wrote:
== Quote from Andrej Mitrovic ([email protected])'s article
Nice work. I've tried it out with allocating some large float arrays,
quick two test cases were a 94MB and 282MB audio file.
File 1 w/o TempAlloc: 410msecs
File 1 w/ TempAlloc: 184msecs
File 2 w/o TempAlloc 1321 msecs
File 2 w/ TempAlloc 567 msecs
Btw, how much *can* I allocate at once by using new (not specific to
TempAlloc)? I've tried a 500MB file, but allocation fails even though
I have plenty of free memory on my system. Is there a limit to using
'new'?
Of course, ideally I'd use some kind of buffering mechanism where a
portion of a file is loaded into memory, and when that's exhausted I'd
load another chunk. But I'd like to know the limits for a single
memory allocation on the garbage-collected heap. Is there some
internal limit for D? I know I can't allocate more than 3GB in the
entire app, but I'm looking at single allocations.
Pardon me if this all sounds stupid, I'm a complete newb when it comes
to memory allocation mechanics. :)
Ironically, these benchmarks just show that the C heap is faster than
the D GC
heap. They are well over the 4 MB mark, where TempAlloc just falls back
on the C
heap. As far as how much you can allocate on the GC heap, it boils down
to how
much **contiguous** free space you have in your address space. Since
32-bit
address space is only 4 GB (and only 2 GB for user space on Win32), I'm
not
surprised you can't allocate more than 500 MB.
I think you are wrong about contiguous memory block. I believe virtual
address space is divided into blocks (which are, indeed, contiguous) but
the address space itself is not. What I mean is that if you try to
allocate 1GB of memory, an OS might succeed that even if the physical
memory is "fragmented" by other processes.
This isn't the case for ALL operating systems, though.
I've believe some OSes don't even allocate memory physically until you
actually access it (by reading or writing to it), and even then they may
only allocate memory for requested pages only.
I might be wrong though.
