When dealing with performances, after type instability, the second “culprit” that arises is often memory allocation. But what exactly is memory allocation for Julia? Why it influences performances so strongly ? What are examples of typical operations that do “allocate” and what are operations that …

[image] fins: It is the management of that memory, not the allocation or freeing - rather all the work, neccessary, to even decide whether or not some piece of memory needs to be freed. :wink: Right, what I’m saying is that typically there will be sprinkled around a bunch of C code some extra…

[image] fins: Yes, I’ve said, that in case of non-gc languages, they typically have a lot less overhead, as they simply do not manage your memory, for you. But this has (from my pov) nothing to do with malloc - I just hope, I’m now able to get that across. Non-GC language, at least C (and C++…

See also Mimalloc test by gbaraldi · Pull Request #47062 · JuliaLang/julia · GitHub which is an experiment to switch the malloc Julia uses. It shows some fairly major advantages.

[image] dlakelan: Right, what I’m saying is that typically there will be sprinkled around a bunch of C code some extra instructions to decide whether to call free on something… This may be about as much overhead as a mark-sweep cycle but paid for in microsecond increments all around the code rat…

You have to do as many (or fewer) allocations in a GC language. And in a non-GC language you may do one free for each malloc (if more a bug, if less potentially a bug, a leak). In a GC-language you do as many free (or fewer) as in a non-GC language. It’s only about the “GC overhead.” If you have ge…

[image] Palli: Ironically Julia is fast as a GC language, when you avoid the GC (which is easy, just not always done), There is nothing ironic, about that. It is a well-known fact, that if you are able to program in a way, that no gc is needed and you switch it off, then your program runs fas…

And one more thing, in C or C++ if you code is serial, then you force your free (and malloc) to be done serially at basically random times. In Julia and GC languages, frees can be batched up (and faster because of cache-effects, I don’t believe C and C++ would to that though seemingly theoretically…

[image] fins: It is a well-known fact, that if you are able to program in a way, that no gc is needed and you switch it off, then your program runs faster. In many cases this is true, in the general case it is not. For example some GC languages do generational copying garbage collection which…

[image] dlakelan: Basically what I’m saying is GC is not just one thing, it’s a bunch of different strategies, and it can be faster than explicit memory management. It often isn’t but it’s not a given that it must be slower, which a lot of people think is true. yep, I’m aware. I’ve (loosely) …

[image] dlakelan: [image] fins: It is a well-known fact, that if you are able to program in a way, that no gc is needed and you switch it off, then your program runs faster. In many cases this is true Is that true ever (in Julia at least)? No; if you avoid allocations (i.e. the GC) the…

What exactly is "allocation" in Julia?

General Usage Performance

lmiq November 4, 2022, 2:19pm 46

I once started a common allocation mistakes thread here: Common allocation mistakes

4 Likes

Topic		Replies	Views
GC occurs at the worst time in tight loop (Garbage Collection) Performance question	93	3891	November 7, 2023
Do Garbage Collectors necessarily make code slow? Offtopic garbage-collection	23	1873	April 27, 2023
Julia GC, heap fragmentation, out of memory, push!/append! Internals & Design	30	2867	May 20, 2024
Improved allocation design, with 4-byte pointers, and sometimes 5-byte in effect Internals & Design	10	901	December 12, 2024
Julia position in the Debian Benchmark Game can be improved, and categorization of some Julia there is unfair Performance	29	2151	December 12, 2024

What exactly is "allocation" in Julia?

Related topics