Under what circumstances would Julia allocate memory to single digits?

Asked Dec 30 '20 at 21:27

Active Dec 30 '20 at 21:27

Viewed 78 times

Suppose I write this function

    function test_function(T)
        c = 1
        d = 31
        q = 321
        b = 32121
        a = 10
        for i in 1:T
            c = d + q + b + a
        end
    end

There will be no memory allocation. However, in my own code, I wrote a similar loop, but I encounter a huge amount of memory allocation. I can't share the entirety of my code, but when I used --track-allocation=user, I see the following results

    80000     q      = 3
        -     p      = 0.1
        -     p_2    = 3
        -     q_2    = .2
        -
   240000     r      =  p - p_2 + q_2 - q;

The code above is in a for loop. This is just strange to me - why would Julia ever allocate memory to single digits?

asked Dec 30 '20 at 21:27

user1691278

1,751
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The key here is type stability. Your code is doing conversions between `Int` and `Float64` – Oscar Smith Dec 30 '20 at 21:31
@OscarSmith How can I resolve this issue? Do you happen to have an example? Thanks! – user1691278 Dec 30 '20 at 21:33
Try `q = 3.0` and `p2=2.0` – Przemyslaw Szufel Dec 30 '20 at 21:38
1

@PrzemyslawSzufel it helped! – user1691278 Dec 30 '20 at 22:32
3

This is very strange. Type promotions like this should have zero cost. And they _definitely_ should not trigger _allocations_! What's going on? – DNF Dec 30 '20 at 23:26
2

It's not a complete [MWE](https://stackoverflow.com/help/minimal-reproducible-example). There must be other assignments to `q` and `r` that we're not seeing here. – mbauman Dec 31 '20 at 04:20

Under what circumstances would Julia allocate memory to single digits?

0 Answers0