4 ms·

You know what I mean. If this was a real world program where those million tasks actually performed work, then this stack space is available for the application

You know what I mean. If this was a real world program where those million tasks actually performed work, then this stack space is available for the application to do that work. It’s not memory that’s consumed by the runtime, it’s memory the runtime expects the program to use - it’s just that this program does no useful work.

aeturnum 2y ago
I am not u/masklinn - but I don't know what you mean. Doesn't the runtime consume memory by setting it aside for future use? Like what else does "using" ram mean other than claiming it for a time?
- hatefulmoron 2y ago
  I think he means that if the Go code had done something more useful, it would use about the same amount of memory. Compare that to another implementation, which might allocate nearly no memory when the tasks don't do anything significant but would quickly catch up to Go if they did.
- jakewins 2y ago
  If the example was extended to, say, once the sleep is completed then parse and process some JSON data (simulating the sleep being a wait on some remote service), then how would memory use be affected? In the Go number reported, the majority of the memory is the stack Go allocated for the application code anticipating processing to happen. In the Node example, the processing instead will need heap allocation. Point being that the two numbers are different - one measures just the overhead of the runtime, the other adds the memory reserved for the app to do work. The result then looks wasteful for Go because the benchmark.. doesn’t do anything. In a real app though, preallocating stack can often be faster than doing just-in-time heap allocation. Not always of course! Just noting that the numbers are different things; one is runtime cost, one is runtime cost plus an optimization that assumes memory will be needed for processing after the sleep.
  - aeturnum 2y ago
    I mean, so I guess you are saying that other languages are better at estimating the memory usage than Go - as go will never need this memory it has allocated? Like Go knows everything that will happen in that goroutine, it should be able to right-size it. I don't think it "looks" wasteful for Go to allocate memory it should know it doesn't need at compile time - I think it is wasteful. Though it's probably not a meaningful waste most of the time. I agree that it would also be interesting to benchmark some actual stack or heap usage and how the runtimes handle that, but if you are running a massively parallel app you do sometimes end up scheduling jobs to sleep (or perhaps, more likely, to prepare to act but they never do and get cancelled). So I think this is a valid concern, even though it's not the only thing that amtters.
- scott_s 2y ago
  Allocating virtual memory is distinct from actually consuming physical memory (RAM). If a process allocates many pages of virtual memory, but never actually reads or writes to that memory, then it's unlikely that any physical memory backs those pages. In this sense, allocating memory is really just bookkeeping in the operating system. It's when you try to read or write that memory that the operating system will actually allocate physical memory for you. When you first try to access the virtual memory you've allocated, there will be a page fault, causing the OS to determine if you're actually allowed to read or write to it. If you've previously allocated it, then all is good, and the OS will allocate some physical memory for you, and make your virtual memory pointers point to that physical memory. If not, well, then that's a segfault. It's not until you first try to use the memory that you actually consume RAM.
flockonus 2y ago
I'll yield it would be interesting to have a similar benchmark but instead of sleeping - which indeed by itself is nonsense, to instead each task compute a small fib sequence, or write a small file; something like that.

aeturnum 2y ago

I am not u/masklinn - but I don't know what you mean. Doesn't the runtime consume memory by setting it aside for future use? Like what else does "using" ram mean other than claiming it for a time?

hatefulmoron 2y ago
I think he means that if the Go code had done something more useful, it would use about the same amount of memory. Compare that to another implementation, which might allocate nearly no memory when the tasks don't do anything significant but would quickly catch up to Go if they did.
jakewins 2y ago
If the example was extended to, say, once the sleep is completed then parse and process some JSON data (simulating the sleep being a wait on some remote service), then how would memory use be affected? In the Go number reported, the majority of the memory is the stack Go allocated for the application code anticipating processing to happen. In the Node example, the processing instead will need heap allocation. Point being that the two numbers are different - one measures just the overhead of the runtime, the other adds the memory reserved for the app to do work. The result then looks wasteful for Go because the benchmark.. doesn’t do anything. In a real app though, preallocating stack can often be faster than doing just-in-time heap allocation. Not always of course! Just noting that the numbers are different things; one is runtime cost, one is runtime cost plus an optimization that assumes memory will be needed for processing after the sleep.
- aeturnum 2y ago
  I mean, so I guess you are saying that other languages are better at estimating the memory usage than Go - as go will never need this memory it has allocated? Like Go knows everything that will happen in that goroutine, it should be able to right-size it. I don't think it "looks" wasteful for Go to allocate memory it should know it doesn't need at compile time - I think it is wasteful. Though it's probably not a meaningful waste most of the time. I agree that it would also be interesting to benchmark some actual stack or heap usage and how the runtimes handle that, but if you are running a massively parallel app you do sometimes end up scheduling jobs to sleep (or perhaps, more likely, to prepare to act but they never do and get cancelled). So I think this is a valid concern, even though it's not the only thing that amtters.
scott_s 2y ago
Allocating virtual memory is distinct from actually consuming physical memory (RAM). If a process allocates many pages of virtual memory, but never actually reads or writes to that memory, then it's unlikely that any physical memory backs those pages. In this sense, allocating memory is really just bookkeeping in the operating system. It's when you try to read or write that memory that the operating system will actually allocate physical memory for you. When you first try to access the virtual memory you've allocated, there will be a page fault, causing the OS to determine if you're actually allowed to read or write to it. If you've previously allocated it, then all is good, and the OS will allocate some physical memory for you, and make your virtual memory pointers point to that physical memory. If not, well, then that's a segfault. It's not until you first try to use the memory that you actually consume RAM.

flockonus 2y ago

I'll yield it would be interesting to have a similar benchmark but instead of sleeping - which indeed by itself is nonsense, to instead each task compute a small fib sequence, or write a small file; something like that.