Maximum Allocatable Dynamic Memory

Maximum Allocatable Dynamic Memory

[sonatabar bar]

Hi,
I am trying to test what is the maximum allocatable
dynamic memory on a give machine. For my surprise I
see wonders happening, and I don't have an
explaination to it. I understand a bit that, it
doesn't have to do with compilers entirely, and hece
seeking explaination. 
 
this test fails allocating memory for index 68561
which means => allocated memory is (68561000000*8)
bytes =>X
=> X/1024/1024/1024 = 510.82 Gig ???
 
May be I am missing something, tried running it on a 2
& 4 Gig phyiscal memory machines, with a swap space of
8Gig.
 
I shall appreciate any feedback,
Thank you,
Sonata.
==========================================
 
#include <iostream>
// Million entries
#define X_DIM 1000000
using namespace std;
int main()
{
 cout<<"******** MEMORY ALLOCATION TEST:
********"<<endl;
 int size_d = sizeof(double);
 cout<<"Using Double: "<<size_d<<endl;
 int limit_reached = 0;
 double **dd_array;
 unsigned long int i = 0;
 dd_array = new double*[X_DIM];
 while(!limit_reached || i < X_DIM)
 {
        try{
                cerr<<"Trying allocation: "<<i<<endl;
                *(dd_array+i++) = new double[X_DIM];
                cerr<<"\t Allocated memory:
"<<std::scientific<<i*X_DIM<<endl;
        }
        catch(...){
                limit_reached = 1;
                cerr<<"\nUnable to allocate memory for
'Index': "<<i<<endl;
                return 0;
        }
 }
 cout<<"******* SUCCESSFUL MEMORY ALLOCATION
*******"<<endl;
 return(0);
}

Thank you,
Sonata.

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Re: Maximum Allocatable Dynamic Memory

[Ian Lance Taylor]

sonatabar bar <sonatabar@yahoo.com> writes:

> I am trying to test what is the maximum allocatable
> dynamic memory on a give machine. For my surprise I
> see wonders happening, and I don't have an
> explaination to it. I understand a bit that, it
> doesn't have to do with compilers entirely, and hece
> seeking explaination. 
>  
> this test fails allocating memory for index 68561
> which means => allocated memory is (68561000000*8)
> bytes =>X
> => X/1024/1024/1024 = 510.82 Gig ???
>  
> May be I am missing something, tried running it on a 2
> & 4 Gig phyiscal memory machines, with a swap space of
> 8Gig.

Wrong mailing list.  This is not a gcc question.  It is a kernel or a
library question.

I believe the answer is that the kernel permits you to allocate as
many pages as you like, but when you actually try to use them and it
looks for a place to put them, it will fail.  I am not an expert,
though.

Ian