Re: allocate memory in userspace

[Erik Andersen <andersen@codepoet.org>]

On Tue Jul 02, 2002 at 01:44:18AM -0700, William Lee Irwin III wrote:
> On Mon, Jul 01, 2002 at 11:49:13AM -0600, Erik Andersen wrote:
> >> void *malloc(size_t size)
> >> {
> >>     void *result;
> >>     if (size == 0)
> >> 	return NULL;
> >>     result = mmap((void *) 0, size + sizeof(size_t), PROT_READ | PROT_WRITE, 
> >> 	    MAP_PRIVATE | MAP_ANONYMOUS, 0, 0);
> >>     if (result == MAP_FAILED)
> >> 	return 0;
> >>     * (size_t *) result = size;
> >>     return(result + sizeof(size_t));
> >> }
> 
> On Tue, Jul 02, 2002 at 01:37:37AM -0700, William Lee Irwin III wrote:
> > This looks like a very bad idea. Userspace allocators should make some
> > attempt at avoiding diving into the kernel at every allocation like this.
> 
> Sorry, I also forgot the rather severe internal fragmentation this is
> likely to suffer due to page-level restrictions on mmap's operation.

Of course.  No question there -- actually using such an allocator
(with a standard linux kernel) would be a terrible idea.  I was
merely providing a trivial answer to his question on how to use
mmap to allocate memory.

 -Erik

--
Erik B. Andersen             http://codepoet-consulting.com/
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