Re: allocate memory in userspace

[William Lee Irwin III <wli@holomorphy.com>]

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.

Cheers,
Bill