[Vm-dev] Measuring allocations

[Jan Vrany]

On Thu, 2017-06-01 at 07:52 -0700, Eliot Miranda wrote:
>  
> Hi Jan,
> 
> > On Jun 1, 2017, at 1:17 AM, Jan Vrany <jan.vrany at fit.cvut.cz>
> > wrote:
> > 
> > 
> > Hi folks, 
> > 
> > Having a Spur VM, I wonder how to measure heap allocations made 
> > by a process executing a particular block, from within the image. 
> > For example, let's have following block: 
> > 
> > [
> >   | a |
> > 
> >   100 timesRepeat: [
> >      a := Array new: 100 
> >   ]
> > ]. 
> > 
> > When run, this block allocates - if I'm correct - some 100 *
> > (<object
> > header size> + 4*100) bytes. 
> 
> Plus the block arg to timesRepeat:.  And the size of an Array in 32-
> bits is
> 

Sure, sure. The exact number is not important for me right now.

> > Note that: 
> > * Ideally, I'd like to exclude allocations made by other threads 
> 
> Then run at high priority.

Good point, thanks. I always forget about that. 

> 
> >   but having allocations made by all threads would be OK too. 
> > * Block can span multiple scavenges even oldspace collects. 
> > * As shown in the example above, I need to take garbage into 
> >   an account.
> > 
> > How to best measure this? 
> 
> What exactly do you want to measure? 

I want to know how much given code allocates. For example that
given piece of code in total allocated 2.5GB. Say. 


>  There is no allocation count, as that would slow down allocation. 

Fair enough. 

>  Time taken to allocate  would be derived by sending timeTiRun to the
> above and subtracting the time for a null loop to run, and the time
> taken in GC.
> 
> The time taken in GC is maintained by the vm.  See vmParameterAt: and
> surrounding.  If you open the About Squeak dialog in a Squeak image
> this is nicely displayed in the VM Stats tab (IIRC).

It is indeed. But in this case I'm not interested in time spent in GC 
:-) 

Thanks, Jan