Messages in this thread | | | Date | Wed, 20 Mar 2013 02:12:54 -0400 | From | Naoya Horiguchi <> | Subject | Re: [PATCH 5/9] migrate: enable migrate_pages() to migrate hugepage |
| |
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
| |