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Date: Tue, 29 Jul 2003 10:28:52 +0530 (IST)
From: Nagendra Singh Tomar <nagendra_tomar@adaptec.com>
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To: Tung-Han Hsieh <thhsieh@xcin.phys.ntu.edu.tw>
cc: linux-kernel@vger.kernel.org, <jamagallon@able.es>
Subject: Re: malloc problem to allocate very large blocks
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AFAIK malloc will not return you memory more than the total virtual memory 
(RAM+swap) in the system. So if you want more than 2GB allocations from 
malloc, make sure you have at least 2GB virtual mem, keeping aside some 
space for the kernel.

--tomar

On Mon, 28 Jul 2003, Tung-Han Hsieh wrote:

> Hello,
> 
> I am developing applications which requires more than 2GB memory.
> But I found that in my Linux system the malloc() cannot allocate
> more than 2GB memory. Here is the details of my system:
> 
> CPU:    Pentium 4 2.53 GHz
> RAM:    2 GB
> Swap:   512 MB
> OS:	Debian-3.0 stable
> Kernel: 2.4.20
> gcc:	2.95.4 20011002
> glibc:  2.2.5-6
> 
> In theory, in a 32-bits machine the maximum allocatable memory
> is up to 4GB. But in the following very simple testing program:
> 
> =====================================================================
> #include <stdio.h>
> #include <stdlib.h>
> 
> main()
> {
>     size_t l;
>     char *s1=NULL, *s2=NULL;
> 
>     l = 1024*1024*1024;
> 
>     s1 = malloc(l);
>     s2 = malloc(l);
>     if (! s1) printf("s1 malloc failed\n");
>     if (! s2) printf("s2 malloc failed\n");
> }
> =====================================================================
> 
> only the block for s1 can be allocated. Further, if I change the
> program to
> 
> =====================================================================
> #include <stdio.h>
> #include <stdlib.h>
> 
> main()
> {
>     size_t l;
>     char *s1=NULL;
> 
>     l = 2*1024*1024*1024;
> 
>     s1 = malloc(l);
>     if (! s1) printf("s1 malloc failed\n");
> }
> =====================================================================
> 
> the gcc complier complain to me that "foo.c:9: warning: integer overflow
> in expression" during the compilation (I use: "gcc foo.c" to compile
> it),
> and the block for s1 cannot be allocated at all. I am wondering if there
> is any way to overcome the 2GB limit.
> 
> Thank you very much for your reply in advance.
> 
> 
> Best Regards,
> 
> T.H.Hsieh
> -
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