Reason for doing malloc / bzero over calloc (performance)?

[Ed Schouten]

* Garrett Cooper <youshi10 at u.washington.edu> wrote:
>  Garrett Cooper wrote:
> >    Title says it all -- is there a particular reason why malloc/bzero 
> > should be used instead of calloc?
> > -Garrett
>  As someone just brought to my attention, I should do some Googling.
> 
>  Initial results brought up this: 
>  <http://boredzo.org/blog/archives/2006-11-26/calloc-vs-malloc>.

To be more precise; I took a look at the source code of calloc on my
FreeBSD 6 box:

| void *
| calloc(num, size)
|         size_t num;
|         size_t size;
| {
|         void *p;
| 
|         if (size != 0 && SIZE_T_MAX / size < num) {
|                 errno = ENOMEM;
|                 return (NULL);
|         }
| 
|         size *= num;
|         if ( (p = malloc(size)) )
|                 bzero(p, size);
|         return(p);
| }

This means that the results on that website would be quite different
than the the ones that the FreeBSD 6 malloc/calloc should give. There is
even a difference between calloc'ing 10 block of 10 MB and 1 block of
100 MB, which shouldn't make a difference here. calloc doesn't have any
performance-advantage here, because it just calls malloc/bzero.

When looking at FreeBSD -CURRENT's calloc (won't paste it; too long), it
just does a arena_malloc/memset (which is malloc/bzero) for small
allocations but a huge_malloc for big allocations (say, multiple pages
big). The latter one already returns pages that are zero'd by the
kernel, so I suspect the calloc performance for big allocations on
-CURRENT is a lot better than on FreeBSD 6. As with FreeBSD 6, it
wouldn't matter if you calloc 10 pieces of 10 MB or one piece of 100 MB.

Yours,
-- 
 Ed Schouten <ed at fxq.nl>
 WWW: http://g-rave.nl/
-------------- next part --------------
A non-text attachment was scrubbed...
Name: not available
Type: application/pgp-signature
Size: 187 bytes
Desc: not available
Url : http://lists.freebsd.org/pipermail/freebsd-hackers/attachments/20070613/82597bc8/attachment.pgp