[Vm-dev] Re: [squeak-dev] What is meant by 'shrink' in the VM parameters?

John M McIntosh johnmci at smalltalkconsulting.com
Fri Oct 22 16:23:11 UTC 2010

It *would* give the memory back to the operating system. 
But we don't anymore again read the following

/* Note:
*   The code allows memory to be overallocated; i.e., the initial
*   block is reserved via mmap() and then the unused portion
*   munmap()ped from the top end.  This is INHERENTLY DANGEROUS since
*   malloc() may randomly map new memory in the block we "reserved"
*   and subsequently unmap()ped.  Enabling this causes crashes in
*   Croquet, which makes heavy use of the FFI and thus calls malloc()
*   all over the place.
*   For this reason, overallocateMemory is DISABLED by default.
*   The upshot of all this is that Squeak will claim (and hold on to)
*   ALL of the available virtual memory (or at least 75% of it) when
*   it starts up.  If you can't live with that, use the -memory
*   option to allocate a fixed size heap.

On 2010-10-22, at 6:24 AM, Ken Causey wrote:

> I'm wondering what 'shrink' means in the following VM parameter
> comments:
> "24 memory threshold above which shrinking object memory (rw)"
> and
> "32 number of shrink memory requests (read-only)"
> My first thought is that a shrink represents Squeak release memory back
> to the operating system once it is no longer needed.
> As I've mentioned before we are trying to reduce the RAM footprint of
> the www.squeak.org process and are watching various related figures.
> We can see the value in VM parameter 32 increase, but while the value
> for parameter 3 (end of memory) goes down as you would expect, the
> operating system's view of the memory usage does not change.
> Ken

John M. McIntosh <johnmci at smalltalkconsulting.com>   Twitter:  squeaker68882
Corporate Smalltalk Consulting Ltd.  http://www.smalltalkconsulting.com

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