growing and shrinking ObjectMemory
Bert Freudenberg
bert at isg.cs.uni-magdeburg.de
Mon Mar 5 07:58:58 UTC 2001
On Sat, 3 Mar 2001, Jan Bottorff wrote:
> I seem to remember from ParcPlace days some OS's having a REALLY ugly issue
> about demand committed memory.
>
> It goes like this, you allocate a bunch of memory/address space that's
> backed by demand zero filled memory. The call to this allocation works
> fine, and your software "thinks" it has the memory. Time passes, and other
> applications use up some swap space. Eventually, your app decided to
> actually touch one of those pages it allocated way back when, and uh oh,
> the swap file is full. So how do you not inform the app that memory it
> allocated, is actually unavailable? If the original allocated had failed,
> the program logic could probably cope. Is the VM prepared to get a swap
> file full memory access fault anytime it might be writing to memory for the
> first time?
It's not.
A funny (not so) thing to note is that I can run four times "squeak
-memory 128M" but not once "squeak -memory 256M". There's "not enough
memory" for the latter, while the first succeeds. I haven't actually
tested what happens if I trash the memory in the first example, but I'd
expect ugly things X-/
-- Bert
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