Re: [RFC PATCH 6/6] powerpc/kvm: change the condition of identifying hugetlb vm

Scott Wood
2015-07-06T21:34:56Z

On Fri, 2015-07-03 at 16:47 +0800, wenwei tao wrote:
> Hi Scott
>
> Thank you for your comments.
>
> Kernel already has that function: is_vm_hugetlb_page() , but the
> original code didn't use it,
> in order to keep the coding style of the original code, I didn't use it
> either.
>
> For the sentence like: "vma->vm_flags & VM_HUGETLB" , hiding it behind
> 'is_vm_hugetlb_page()' is ok,
> but the sentence like: "vma->vm_flags &
> (VM_LOCKED|VM_HUGETLB|VM_PFNMAP)" appears in the patch 2/6,
> is it better to hide the bit combinations behind the
> is_vm_hugetlb_page() ? In my patch I just replaced it with
> "vma->vm_flags & (VM_LOCKED|VM_PFNMAP) || (vma->vm_flags &
> (VM_HUGETLB|VM_MERGEABLE)) == VM_HUGETLB".

If you're going to do non-obvious things with the flags, it should be done in
one place rather than throughout the code. Why would you do the above and
not "vma->vm_flags & (VM_LOCKED | VM_PFNMAP) || is_vm_hugetlb_page(vma)"?

-Scott