On 3/12/16 9:52 PM, Brian Barnes wrote:
This is key:
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Memory_Management
When the mozilla docs refer to GC, they refer to mark-and-sweep objects
created by the user’s code.
User code creates lots of objects in Firefox whose memory management
model is not mark-and-sweep at the moment (for example, DOM nodes).
The docs you are looking at there are specifically for SpiderMonkey, not
SpiderMonkey in a particular (browser) embedding.
I think this is all that needs to be done.
Not if you're actually trying to avoid memory collection pauses,
sorry... This is what makes all this rather annoying.
There’s certain other things that goes on, but they are things out of
control of the coder. The objects the code creates are what we are
interested in.
OK. Note that you can have some control over things the browser creates
too, not just things you create.
But again, the definition of "GC" as described on the page you link to
doesn't cover everything that's touched by "GC" as it matters for an
actual page in a web browser...
We’re not talking past each other, we are talking at different levels of
grain. I’m talking about what the end user experiences; which is
numerous quick GCs usually followed by a large GC. You are talking
about the actual mechanics of what each of those GCs actually are, or
do, but to the end user, they are quick pauses and large pauses.
OK. Say I have some gc pauses: 100us, 1ms, 5ms, 10ms, 20ms, 50ms, 600ms.
Which of those are quick pauses and which are large? As far as I can
tell, the answer depends on the application, what sort of real-time
guarantees it needs, and how much processing it does itself. About the
only thing everyone would agree on is that 100us is small and 600ms is
large.
But this has de-evolved; let’s reduce this to the regular mark-and-sweep
collection of objects.
That would correspond to the first three modes I described, but even
within that a given mode can in theory lead to either a quick pause or a
large one, and you don't necessarily know up front which it will be.
In practice, all the modes are incremental and aim to not have anything
resembling 600ms pauses. But if 5ms constitutes a "large" pause for
you, then you might end up with "large" pauses from at least two of the
modes. Not sure whether a nursery collection can ever end up there...
But my larger point is that if we define this to be "regular
mark-and-sweep collection of objects" that might well not be enough to
avoid big memory collection pauses in the future anyway. And if we
don't define it to be that, then it's not clear what to define it to be
because it really depends on what else is going on...
-Boris
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