Re: [PATCH 0/7] [RFC] hugetlb: pagetable_operations API (V2)

[Dave Hansen <hansendc@us.ibm.com>]

On Mon, 2007-03-19 at 13:05 -0700, Adam Litke wrote:
> For the common case (vma->pagetable_ops == NULL), we do almost the
> same thing as the current code: load and test.  The third instruction
> is different in that we jump for the common case instead of jumping in
> the hugetlb case.  I don't think this is a big deal though.  If it is,
> would an unlikely() macro fix it? 

I wouldn't worry about micro-optimizing it at that level.  The CPU does
enough stuff under the covers that I wouldn't worry about it at all.

I wonder if the real differential impact (if any) is likely to come from
the pagetable_ops cacheline being hot or cold, since it is in a
different place in the structure than the flags.  But, from a quick
glance I see a few vm_ops references preceding pagetable_ops references,
so the pagetable_ops cacheline might already be hot most of the time.  

BTW, are there any other possible users for these things other than
large pages?

-- Dave