On Fri, Jun 23, 2017 at 5:22 AM, CFK <cfkar...@gmail.com> wrote:
> On Jun 22, 2017 9:32 AM, "Chris Angelico" <ros...@gmail.com> wrote:
>
> On Thu, Jun 22, 2017 at 11:24 PM, CFK <cfkar...@gmail.com> wrote:
>> When
>> I draw memory usage graphs, I see sawtooth waves to the memory usage which
>> suggest that the garbage builds up until the GC kicks in and reaps the
>> garbage.
>
> Interesting. How do you actually measure this memory usage? Often,
> when a GC frees up memory, it's merely made available for subsequent
> allocations, rather than actually given back to the system - all it
> takes is one still-used object on a page and the whole page has to be
> retained.
>
> As such, a "create and drop" usage model would tend to result in
> memory usage going up for a while, but then remaining stable, as all
> allocations are being fulfilled from previously-released memory that's
> still owned by the process.
>
>
> I'm measuring it using a bit of a hack; I use psutil.Popen
> (https://pypi.python.org/pypi/psutil) to open a simulation as a child
> process, and in a tight loop gather the size of the resident set and the
> number of virtual pages currently in use of the child. The sawtooths are
> about 10% (and decreasing) of the size of the overall memory usage, and are
> probably due to different stages of the simulation doing different things.
> That is an educated guess though, I don't have strong evidence to back it
> up.
>
> And, yes, what you describe is pretty close to what I'm seeing. The longer
> the simulation has been running, the smoother the memory usage gets.
Ah, I think I understand. So the code would be something like this:
Phase one:
Create a bunch of objects
Do a bunch of simulation
Destroy a bunch of objects
Simulate more
Destroy all the objects used in this phase, other than the result
Phase two:
Like phase one
In that case, yes, it's entirely possible that the end of a phase
could signal a complete cleanup of intermediate state, with the
consequent release of memory to the system. (Or, more likely, a
near-complete cleanup, with release of MOST of memory.)
Very cool bit of analysis you've done there.
ChrisA
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