I'm trying to understand some garbage collection behavior I'm seeing with
V8 / Chrome. The scenario is that I have a small program that receives ~
1MiB of image data from a websocket at a rate of about 60Hz.
Minimal receiving code looks like this:
var connection = new WebSocket('ws://127.0.0.1:31333');
connection.onmessage = message => {
var dataCopy = new Uint8Array(message.data, 0);
};
Profiling in Chrome shows a saw tooth of allocations rising until a major
garbage collection occurs, repeating at regular intervals. The allocations
are all exactly 176 bytes, which doesn't really match up with the expected
1 MiB. I also took a heap snapshot and dug through it a bit but couldn't
see anything useful that was 176 bytes in size.
I found an excellent overview of V8 GC (https://v8.dev/blog/trash-talk). If
I understand correctly it seems a little surprising that I'm seeing major
GC events when a minor scavenge type GC could probably pick up those
allocations. Additionally, as mentioned above, the allocations seen while
profiling don't have the expected size of 1MiB.
I understand that there's a "large object space" which is possibly where
the allocations are actually ending up. Unfortunately I can't find any
references to "large object space" at https://v8.dev/docs.
Can anyone help me understand:
Why I see this behaviour with major GC's happening regularly?
Why are the allocations smaller than expected?
If it's related to large object handling are there any resources that
explain how large objects are handled in V8 / Chrome and what the limits
around them are?
I'm using Chrome Version 81.0.4044.113 (Official Build) (64-bit)) and
Windows 10 Pro 1903 if that's helpful.
Thanks
[image: g1.PNG] <about:invalid#zClosurez>
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