On Tue, Mar 19, 2013 at 08:11:13AM +0100, Michal Hocko wrote:
> On Mon 18-03-13 20:07:16, Naoya Horiguchi wrote:
> > On Mon, Mar 18, 2013 at 04:40:57PM +0100, Michal Hocko wrote:
> > > On Thu 21-02-13 14:41:44, Naoya Horiguchi wrote:
...
> > > > @@ -536,6 +557,11 @@ static inline int check_pmd_range(struct vm_area_struct *vma, pud_t *pud,
> > > > pmd = pmd_offset(pud, addr);
> > > > do {
> > > > next = pmd_addr_end(addr, end);
> > > > + if (pmd_huge(*pmd) && is_vm_hugetlb_page(vma)) {
> > >
> > > Why an explicit check for is_vm_hugetlb_page here? Isn't pmd_huge()
> > > sufficient?
> >
> > I think we need both check here because if we use only pmd_huge(),
> > pmd for thp goes into this branch wrongly.
>
> Bahh. You are right. I thought that pmd_huge is hugetlb thingy but it
> obviously checks only _PAGE_PSE same as pmd_large() which is really
> unfortunate and confusing. Can we make it hugetlb specific?
I agree that we had better fix this confusion.
What pmd_huge() (or pmd_large() in some architectures) does is just
checking whether a given pmd is pointing to huge/large page or not.
It does not say which type of hugepage it is.
So it shouldn't be used to decide whether the hugepage are hugetlbfs or not.
I think it would be better to introduce pmd_hugetlb() which has pmd and vma
as arguments and returns true only for hugetlbfs pmd.
Checking pmd_hugetlb() should come before checking pmd_trans_huge() because
pmd_trans_huge() implicitly assumes that the vma which covers the virtual
address of a given pmd is not hugetlbfs vma.
I'm interested in this cleanup, so will work on it after this patchset.
Thanks,
Naoya
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