15.11.08 в 00:56 bearophile в своём письме писал(а):
While allocating lot of memory for a little memory-hungry program, I
have found results that I don't understand. So I have written the
following test programs. Maybe someone can give me some information on
the matter.
I am using a default install of a 32 bit Win XP with 2 GB RAM (so for
example I can't allocate 3 GB of RAM). (I presume answers to my
questions are Windows-related).
From C (MinGW 4.2.1) this is about the largest memory block I can
allocate (even it swaps and requires 7+ seconds to run), 1_920_000_000
bytes:
#include "stdio.h"
#include "stdlib.h"
#define N 480000000
int main() {
unsigned int* a = (unsigned int*)malloc(N * sizeof(unsigned int));
unsigned int i;
if (a != NULL)
for (i = 0; i < N; ++i)
a[i] = i;
else
printf("null!");
return 0;
}
But from D this is about the largest memory block I can allocate with
std.c.stdlib.malloc, 1_644_000_000 bytes, do you know why the difference?
//import std.gc: malloc;
import std.c.stdlib: malloc;
void main() {
const uint N = 411_000_000;
uint* a = cast(uint*)malloc(N * uint.sizeof);
if (a !is null)
for (uint i; i < N; ++i)
a[i] = i;
else
printf("null!");
}
(If I use std.gc.malloc the situation is different yet, and generally
worse).
-----------------------
So I have tried to use a sequence of smaller memory blocks, this is the
C code (every block is about 1 MB):
#include "stdio.h"
#include "stdlib.h"
#define N 250000
int main(int argc, char** argv) {
unsigned int i, j;
unsigned int m = argc == 2 ? atoi(argv[1]) : 100;
for (j = 0; j < m; ++j) {
unsigned int* a = (unsigned int*)malloc(N * sizeof(unsigned
int));
if (a != NULL) {
for (i = 0; i < N; ++i)
a[i] = i;
} else {
printf("null! %d\n", j);
break;
}
}
return 0;
}
And the D code:
//import std.gc: malloc;
import std.c.stdlib: malloc;
import std.conv: toUint;
void main(string[] args) {
const uint N = 250_000;
uint m = toUint(args[1]);
for (uint j; j < m; ++j) {
uint* a = cast(uint*)malloc(N * uint.sizeof);
if (a !is null) {
for (uint i; i < N; ++i)
a[i] = i;
} else {
printf("null! %d\n", j);
break;
}
}
}
With such code I can allocate 1_708_000_000 bytes from D and up to
2_038_000_000 bytes from C (but near the last 100-200 MB of RAM the C
code swaps a lot).
So can't I can't use all my RAM from my D code? And do you know why?
Bye,
bearophile
Comparison DMD against DMC might be more consistent since they share the
same CRT.
