Re: your mail

[Maciej Zenczykowski]

On Tue, 10 Feb 2004, Bloch, Jack wrote:

> I have a system with 2GB of memory. One of my processes calls mmap to try to
> map a 100MB file into memory. This calls fails with -ENOMEM. I rebuilt the
> kernel with a few debug printk statements in mmap.c to see where the failure
> was occurring it occurred in the function arch_get_unmapped_area. the code
> is as follows:
> 
> for (vma = find_vma(mm, addr); ; vma = vma->vm_next) {
> 		/* At this point:  (!vma || addr < vma->vm_end). */
> 		unsigned long __heap_stack_gap;
> 		if (TASK_SIZE - len < addr)
>                 { 

it's valid there's no point in searching further for an area of at least 
len bytes.  The user area is 0 .. TASK_SIZE-1.  The addr is the address 
currently being checked, the len is the requested length.  if addr+len is 
greater or equal to TASK_SIZE then the current addr (which is increasing 
within this loop) already causes such a mapping to overflow into kernel 
space (exceeds the TASK_SIZE virtual address limit).  This is precisely as 
expected.

I'd assume your program has fragmented memory to such a level that a 
single consecutive 100 MB area is no longer free (not that hard to do, 
since TASK_SIZE is 3 GB).

Cheers,
MaZe.


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