Re: mmap(2) performance netbsd-1-6 vs. -current

On Sunday, October 19, 2003, at 09:51  AM, Bang Jun-Young wrote:

> The test program used is as follows (please don't blame me for its
> silliness, I just wanted to see a rough difference in minutes :-):

Ok, I'll ignore the silliness, but I will point out a couple of bugs :-)

> #include <stdio.h>
> #include <sys/mman.h>
>
> main()
> {
> 	void *ptr[15];
> 	int i, j;
> 	size_t size;
>
> 	for (j = 0; j < 40960; j++) {
> 		for (i = 0; i < 15; i++) {
> 			size = 4096 << i;
> 			ptr[i] = mmap(NULL, size, PROT_READ|PROT_WRITE, MAP_ANON, -1, 0);
> 			if (ptr == NULL)
> 				err("NULL returned, i=%d\n", i);

There are two problems with this code:

	- mmap() returns MAP_FAILED, not NULL, on faulure.
	- "ptr" will never be null anyway!  I think you really want to
	  be testing ptr[i].

> 			*((int *)ptr) = 0xdeadbeef;

...and, here again, you want to be dereferencing ptr[i].

> 		}
> 		for (i = 0; i < 15; i++) {
> 			size = 4096 << i;
> 			munmap(ptr[i], size);
> 		}
> 	}
> }
>
> Jun-Young
>
> -- 
> Bang Jun-Young <[email protected]>
>
         -- Jason R. Thorpe <[email protected]>