Let blocks seem not to be fully optimizable...
So rather try using const. This eliminated the allocations for me.
Related issues:
https://github.com/JuliaLang/julia/issues/10224
https://github.com/JuliaLang/julia/issues/7953
Best,
Simon
Am Freitag, 10. Juli 2015 14:29:20 UTC-7 schrieb Zouhair Mahboubi:
>
> I’m trying to optimize my code, and since one of the bottle necks is
> garbage collection, I’ve been trying to get rid of unnecessary memory
> allocation.
>
> In the process, I ended up dealing with this case:
>
> let X = Int64[1,2,3,14]
>
>
> function sub2(X::Vector{Int64}, nNodes::Int64)
> N = length(X)::Int64
> index = X[N]::Int64
> stride = 1::Int64
> for k in (N-1):-1:1
> stride = stride::Int64 * nNodes::Int64
> index += ((X[k]-1)::Int64 * stride::Int64)::Int64
> end
> return index::Int64
> end
>
> #force compiling
> sub2(X,1)
>
> #profile
> @time for j in 1:1e7 sub2(X,21) end
> @time for j in 1:1e7 sub2(X,22) end
>
> end
>
> The result is:
> elapsed time: 0.318801734 seconds (96 bytes allocated)
> elapsed time: 0.434234715 seconds (160000096 bytes allocated, 11.08% gc
> time)
>
> I’m trying to understand why calling the function with n=21 (or lower)
> does not allocate much memory, whereas calling it with n=22 (or higher) is
> causing a lot of memory to be allocated (with the value of X I picked,
> sub2(X,21) =497 and sub2(X,22)=542. I tired with different values of X, and
> if the return value is larger than 512 it ends up allocating more memory,
> if it's less than 512 it does not)
>
> I did my best to make sure types are asserted to avoid type instability.
>
> This does not have a large effect in the big picture, but I am trying to
> wrap my head around how / when memory is allocated.
>
> FWIW, here is the output of running using —track-allocation=all
>
> - let X = Int64[1,2,3,14]
> -
> -
> - function sub2(X::Vector{Int64}, nNodes::Int64)
> 160151688 N = length(X)::Int64
> 0 index = X[N]::Int64
> 0 stride = 1::Int64
> 0 for k in (N-1):-1:1
> 0 stride = stride::Int64 * nNodes::Int64
> 0 index += ((X[k]-1)::Int64 * stride::Int64)::Int64
> - end
> 0 return index::Int64
> - end
> -
> - #force compiling
> - sub2(X,1)
> -
> - #profile
> - @time for j in 1:1e7 sub2(X,21) end
> - @time for j in 1:1e7 sub2(X,22) end
> -
> - end
> test.jl.mem (END)
>
>
