On Wed, Nov 26, 2014 at 4:05 PM, Alexander Duyck
[off-list ref] wrote:

This patch splits the netdev_alloc_frag function up so that it can be used
on one of two page frag pools instead of being fixed on the
netdev_alloc_cache.  By doing this we can add a NAPI specific function
__napi_alloc_frag that accesses a pool that is only used from softirq
context.  The advantage to this is that we do not need to call
local_irq_save/restore which can be a significant savings.

I also took the opportunity to refactor the core bits that were placed in
__alloc_page_frag.  First I updated the allocation to do either a 32K
allocation or an order 0 page.  Then I also rewrote the logic to work from
the end of the page to the start.  By doing this the size value doesn't
have to be used unless we have run out of space for page fragments.
Finally I cleaned up the atomic bits so that we just do an
atomic_sub_return and if that returns 0 then we set the page->_count via an
atomic_set.  This way we can remove the extra conditional for the
atomic_read since it would have led to an atomic_inc in the case of success
anyway.

Nice simplification. Complicated, but looks good to me.
I think only replacement of loop with 32k+page begs
better explanation in the commit log. I'm guessing you're
killing intermediate sizes to simplify the code?

Thank you for doing it. It's a great improvement.