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

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