A GC latency SLO should include operating-system memory pressure. Otherwise, a page-fault problem will look like a collector problem and lead to the wrong fix.
In general when you tune knobs for GC, you pay for benefits in one area with sacrifices in another. Two big knobs to turn are pause latency and throughput. You probably wouldn’t want to go full “optimize for latency” because you’d end up with poor throughput. Also vice versa. Java’s reputation for poor GC performance is partly due to historical defaults that tune it for throughput.
Go’s GC is already a “concurrent mark-sweep garbage collector” and already has “extremely low mutator pause times, on the order of tens of microseconds”. It sounds like on-the-fly is just a different flavor of what Go already has.
It's a well known algorithm. Folks who do GCs for a living know about it. The folks who work on Go are surely aware of it. I'm assuming that they do not use it for a good reason, hence my question!
Fil-C's GC (Fil's Unbelievable Garbage Collector) uses an alternative on-the-fly algorithm, which I call Phil's Concurrent Marking.
Phil's Concurrent Marking differs from DLG in that it only requires a Djikstra barrier and uses a permagrey stack (something that Go used to do).
However, FUGC does clever things for coroutines (as in ucontexts, which Fil-C supports) - they are not permagrey; they only become grey if they execute. That's relevant to Go because Go moved away from permagrey stacks because of coroutine scan overheads, which the FUGC coroutine strategy might avoid.
But even if Go could not go back to permagrey, then the answer would be to use DLG, which would involve using the combined Yuasa+Dijstra barrier, which Go uses today anyway
A GC latency SLO should include operating-system memory pressure. Otherwise, a page-fault problem will look like a collector problem and lead to the wrong fix.
Is there a reason why Go isn’t using on the fly GC, where there’s no STW at all?
What I found when I searched for "on the fly" is this: https://github.com/mthom/on-the-fly-gc — it looks like it has pauses, from the docs.
In general when you tune knobs for GC, you pay for benefits in one area with sacrifices in another. Two big knobs to turn are pause latency and throughput. You probably wouldn’t want to go full “optimize for latency” because you’d end up with poor throughput. Also vice versa. Java’s reputation for poor GC performance is partly due to historical defaults that tune it for throughput.
Go’s GC is already a “concurrent mark-sweep garbage collector” and already has “extremely low mutator pause times, on the order of tens of microseconds”. It sounds like on-the-fly is just a different flavor of what Go already has.
The classic on the fly GC algorithm is DLG, hilariously published in two papers, because the first one had a bug. Here's the second paper: https://caml.inria.fr/pub/papers/doligez_gonthier-gc-popl94....
It's a well known algorithm. Folks who do GCs for a living know about it. The folks who work on Go are surely aware of it. I'm assuming that they do not use it for a good reason, hence my question!
Fil-C's GC (Fil's Unbelievable Garbage Collector) uses an alternative on-the-fly algorithm, which I call Phil's Concurrent Marking.
I've documented it here: https://fil-c.org/fugc
Here's the source: https://github.com/pizlonator/fil-c/blob/deluge/libpas/src/l...
Phil's Concurrent Marking differs from DLG in that it only requires a Djikstra barrier and uses a permagrey stack (something that Go used to do).
However, FUGC does clever things for coroutines (as in ucontexts, which Fil-C supports) - they are not permagrey; they only become grey if they execute. That's relevant to Go because Go moved away from permagrey stacks because of coroutine scan overheads, which the FUGC coroutine strategy might avoid.
But even if Go could not go back to permagrey, then the answer would be to use DLG, which would involve using the combined Yuasa+Dijstra barrier, which Go uses today anyway
What is stopping the author to use latest version of Go and Linux Kernel ?
Yet another reason why "no runtime" is such a huge advantage.