4 ms·

That's less than a fourth of what the article says. Copying data is sometimes faster than allocating it (and the TCMalloc-inspired Go allocator is quite quick.

That's less than a fourth of what the article says. Copying data is sometimes faster than allocating it (and the TCMalloc-inspired Go allocator is quite quick.) Many small, allocations are inefficient in any language... There are other interesting points. And anyway, a bump allocator with nursery will spend longer time vetting the nursery and copying long-lived objects. In Go this would not pay back, as the nursery is mostly staying on the stack without special tricks to please the escape analysis. If you argued that Rust lifetimes system makes it easier to reason like the escape analysis would, I would agree, but you preferred to drop a tweet-size rant...

pcwalton 8y ago
tcmalloc cannot compare to allocation performance in HotSpot, where allocation is about 5 or 6 instructions. This is the same size as a function prologue and epilogue. You're denying that the generational hypothesis holds for Go heap objects. I see no reason why this would be the case. In fact, Go's situation is very close to that of .NET, where the generational hypothesis certainly holds and therefore .NET has a generational garbage collector. This very article is evidence in favor of the generational hypothesis, since much of the optimizations boil down to reducing short-lived heap allocations.
- troytchell 8y ago
  The creators of Go are Rob Pike and Google. I think they would know if a different GC were better and use it. I used to sometimes doubt Rob Pike too and think Go had made some mistakes. After using Go and listening to his talks (like [0]) I realized how wrong I was. There's a reason he has helped build two wildly successful programming languages.. How many have you built? Are you smarter than Google? In the end, embracing Rob Pike's brilliant decisions and taste has made my programming life so much simpler and better. I switched to Acme [1], turned off syntax highlighting on Gitub PR reviews with a userscript[2], and my life is infinitely simpler. Rob Pike has been right on so many things and has made Go successful. I'm sure if a generational GC were better for Go, he would have built and used it, so you're obviously wrong. [0]: https://www.youtube.com/watch?v=rFejpH_tAHM https://www.youtube.com/watch?v=rFejpH_tAHM [1]: http://acme.cat-v.org/ http://acme.cat-v.org/ [2]: https://groups.google.com/d/msg/golang-nuts/hJHCAaiL0so/kG3BHV6QFfIJ https://groups.google.com/d/msg/golang-nuts/hJHCAaiL0so/kG3B...
- lossolo 8y ago
  And again same thing about HotSpot that you repeat third time in last week-two weeks? Java has new GC which is non-generational and is focused on low latency like Go GC is. It's called ZGC. http://openjdk.java.net/jeps/333 http://openjdk.java.net/jeps/333
  - pcwalton 8y ago
    ZGC has a very different design. Go's GC is non-moving and has no read barrier. ZGC has a read barrier and bump allocation everywhere (using compaction to ensure that memory regions are contiguous). As a result it does not suffer the throughput issues of Go's GC.
    - lossolo 8y ago
      It's not moving/compacting because it doesn't need to - it doesn't have fragmentation issues. Bump allocation is efficient and fast in single threaded programs but almost all Go applications are multi threaded and it would require locks there. Go is using thread local caches for allocation, that's why there is no point in using bump allocation. This was mentioned many times by the Go team. Generational hypothesis says that most objects die young. Golang have value types (which Java do not have atm, but Valhalla is coming) and allocate on the stack based on escape analysis (which gets better with time). This means that adding generational GC would not benefit Go as much as you think. Go GC main focus is very low latency, not throughput and handling huge heaps with a lot of generations is not so easy with HotSpot. In many cases you need to tune GC in Java because of that. There are trade offs like with everything. I am running high performance service written in Golang and I was working on high performance services in Java. This are the pauses from Go service on XX GB heaps from today: https://imgur.com/tSXtP4a https://imgur.com/tSXtP4a This is without tuning GC or writing exceptionally unidiomatic Go code. This is impossible to achieve in Java with Hot Spot without tuning GC/writing your whole code specially to satisfy GC.
      - chrisseaton 8y ago
        > Bump allocation is efficient and fast in single threaded programs but almost all Go applications are multi threaded and it would require locks there. If you’re using bump allocation you do it per thread! You don’t do it globally and use a lock!
- gok 8y ago
  But a stack allocation is 0 or 1 instructions.
  - pcwalton 8y ago
    Not if you have to check for stack space, like Go does. It's no coincidence that a bump allocator and a function prologue have exactly the same structure: check against a limit and bump a thread-local pointer. There are runtimes like Chicken Scheme that actually implement heaps using the stack!

pcwalton 8y ago

tcmalloc cannot compare to allocation performance in HotSpot, where allocation is about 5 or 6 instructions. This is the same size as a function prologue and epilogue. You're denying that the generational hypothesis holds for Go heap objects. I see no reason why this would be the case. In fact, Go's situation is very close to that of .NET, where the generational hypothesis certainly holds and therefore .NET has a generational garbage collector. This very article is evidence in favor of the generational hypothesis, since much of the optimizations boil down to reducing short-lived heap allocations.

troytchell 8y ago
The creators of Go are Rob Pike and Google. I think they would know if a different GC were better and use it. I used to sometimes doubt Rob Pike too and think Go had made some mistakes. After using Go and listening to his talks (like [0]) I realized how wrong I was. There's a reason he has helped build two wildly successful programming languages.. How many have you built? Are you smarter than Google? In the end, embracing Rob Pike's brilliant decisions and taste has made my programming life so much simpler and better. I switched to Acme [1], turned off syntax highlighting on Gitub PR reviews with a userscript[2], and my life is infinitely simpler. Rob Pike has been right on so many things and has made Go successful. I'm sure if a generational GC were better for Go, he would have built and used it, so you're obviously wrong. [0]: https://www.youtube.com/watch?v=rFejpH_tAHM https://www.youtube.com/watch?v=rFejpH_tAHM [1]: http://acme.cat-v.org/ http://acme.cat-v.org/ [2]: https://groups.google.com/d/msg/golang-nuts/hJHCAaiL0so/kG3BHV6QFfIJ https://groups.google.com/d/msg/golang-nuts/hJHCAaiL0so/kG3B...
lossolo 8y ago
And again same thing about HotSpot that you repeat third time in last week-two weeks? Java has new GC which is non-generational and is focused on low latency like Go GC is. It's called ZGC. http://openjdk.java.net/jeps/333 http://openjdk.java.net/jeps/333
- pcwalton 8y ago
  ZGC has a very different design. Go's GC is non-moving and has no read barrier. ZGC has a read barrier and bump allocation everywhere (using compaction to ensure that memory regions are contiguous). As a result it does not suffer the throughput issues of Go's GC.
  - lossolo 8y ago
    It's not moving/compacting because it doesn't need to - it doesn't have fragmentation issues. Bump allocation is efficient and fast in single threaded programs but almost all Go applications are multi threaded and it would require locks there. Go is using thread local caches for allocation, that's why there is no point in using bump allocation. This was mentioned many times by the Go team. Generational hypothesis says that most objects die young. Golang have value types (which Java do not have atm, but Valhalla is coming) and allocate on the stack based on escape analysis (which gets better with time). This means that adding generational GC would not benefit Go as much as you think. Go GC main focus is very low latency, not throughput and handling huge heaps with a lot of generations is not so easy with HotSpot. In many cases you need to tune GC in Java because of that. There are trade offs like with everything. I am running high performance service written in Golang and I was working on high performance services in Java. This are the pauses from Go service on XX GB heaps from today: https://imgur.com/tSXtP4a https://imgur.com/tSXtP4a This is without tuning GC or writing exceptionally unidiomatic Go code. This is impossible to achieve in Java with Hot Spot without tuning GC/writing your whole code specially to satisfy GC.
    - chrisseaton 8y ago
      > Bump allocation is efficient and fast in single threaded programs but almost all Go applications are multi threaded and it would require locks there. If you’re using bump allocation you do it per thread! You don’t do it globally and use a lock!
gok 8y ago
But a stack allocation is 0 or 1 instructions.
- pcwalton 8y ago
  Not if you have to check for stack space, like Go does. It's no coincidence that a bump allocator and a function prologue have exactly the same structure: check against a limit and bump a thread-local pointer. There are runtimes like Chicken Scheme that actually implement heaps using the stack!