Benchmarks malloc and free. In main, ntrials is the number of times each allocation is to be executed and meaured nmax is the maximum array length, so total number of measurements is ntrials*nmax. In main, a chart is generated with chartName.writePlot(benchFile, nPoints, 60_000, 1000);, the last two numbers are the maximum value of time (ns) on the vertical axis in each chart for malloc and free respectively, they default to -1 to accept maximum chart range.
The function
auto memoryBench(alias x, string units = "nsecs", uint mask = GC.BlkAttr.NO_SCAN)(long ntrials, long nmax)
is the benchmarking function. The mask template parameter determines how D's garbage collection executes and defaults to a fast mode; units is the time unit described here, the template parameter x is an element instance of what the array should be filled with, it can be of any type.
At the moment the chart is plotted using R's base graphic, here is an example of what the chart looks like: 
The plot sampes data from the created benchmark table, the number of points to sample in the plot is nPoints in main. Set to -1 if you want all the data to be plotted.
You'll need an installation of D and R, also you need the data.table R package installable on the R interpreter with:
install.packages("data.table")
Compile and run with (linux):
dmd allocBench.d -version=verbose && ./allocBench
-version=verbose shows progress messages.
The maximum array size (nmax) is very large by default which will take time, so you might want to change it to something like 10_000 for demo.
Enjoy!
<style> .plot { width: 50vw; } </style>