how to do page level mem alloc in freebsd kernel?

[kalash nainwal]

On Thu, Jul 15, 2010 at 5:41 PM, John Baldwin <jhb at freebsd.org> wrote:
> On Thursday, July 15, 2010 6:28:53 am kalash nainwal wrote:
>> Hi,
>>
>> I want to allocate one (or more) pages in kernel space.
>> I'm not sure what is the api in freebsd (something which
>> is similar to __get_free_pages() of linux).
>>
>> Would malloc(4096, ...) guarantee that the returned
>> address is aligned on page boundary?
>
> Well, malloc(PAGE_SIZE) will align it on a page boundary. :)  malloc(4096)
> will be aligned on a 4096-byte boundary if PAGE_SIZE is >= 4096.  My
> understanding is that objects returned from malloc() are aligned to the
> smallest power-of-2 value >= the requested size up to a page.  Allocations
> larger than a page are page aligned.  So a malloc of 24 bytes or 32 bytes is
> 32-byte aligned for example.
>

Thanks John for explaining.

After going through the kernel src I was not sure about
malloc, as the code is little hard to follow. However I figured
kmem_alloc(kernel_pmap, PAGE_SIZE) would serve my
purpose fine.

Regards,
-Kalash