A question regarding the GC

[torhu]

bearophile wrote:
> If I perform a std.gc.malloc(N), the Phobos GC gives me a pointer P, when I perform a std.gc.realloc(x, 0) it frees the memory, so the GC must remember how much N was (or probably its value rounded to the nearest larger multiple of 4, 8 or 16 bytes).
> So given the pointer P, how can I ask the Phobos GC to quickly tell me how much N was? (and I'd like to know how much approximated such N' value is)
> This will allow me to avoid saving that N value again into my data structures, avoiding wasting space to keep N two times in memory.
> If the Phobos GC API is currently unable to give me this N' value and approximations, can't we modify the GC so it can give us such values?
> 

Are you aware of std.gc.capacity()?  If you want to know what sizes the 
GC rounds to when allocating, you probably need to read the source, 
which comes with dmd.