The backing store of an ArrayBuffer is allocated off the heap. Only a small JS object is allocated on the heap. That's why you see only 176 byte objects in the heap snapshot.
That said, a loop doing "dataCopy = new Uint8Array(message.data, 0);" should trigger only minor GCs unless dataCopy is stored outside and long living. Could you please file a bug at https://bugs.chromium.org/p/v8/issues/list with steps to reproduce for this minor GC vs major GC issue? Cheers, Ulan. On Tue, Apr 21, 2020 at 3:25 PM Euan Burns <burns...@gmail.com> wrote: > 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] > > -- > -- > v8-dev mailing list > v8-dev@googlegroups.com > http://groups.google.com/group/v8-dev > --- > You received this message because you are subscribed to the Google Groups > "v8-dev" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to v8-dev+unsubscr...@googlegroups.com. > To view this discussion on the web visit > https://groups.google.com/d/msgid/v8-dev/e492de7a-b3c5-44d6-9649-a2ee48f41e52%40googlegroups.com > <https://groups.google.com/d/msgid/v8-dev/e492de7a-b3c5-44d6-9649-a2ee48f41e52%40googlegroups.com?utm_medium=email&utm_source=footer> > . > -- -- v8-dev mailing list v8-dev@googlegroups.com http://groups.google.com/group/v8-dev --- You received this message because you are subscribed to the Google Groups "v8-dev" group. To unsubscribe from this group and stop receiving emails from it, send an email to v8-dev+unsubscr...@googlegroups.com. To view this discussion on the web visit https://groups.google.com/d/msgid/v8-dev/CABNJt2%2Bt%2B1nBx%2BEb3noHRwQExA6uwOr4ygpebD%2BE_O1hHSMJCw%40mail.gmail.com.
