Re: [PATCH v5 08/11] thp: setup huge zero page on non-write page fault

David Rientjes
2012-11-15T21:52:49Z

On Thu, 15 Nov 2012, Kirill A. Shutemov wrote:

> > > diff --git a/mm/huge_memory.c b/mm/huge_memory.c
> > > index f36bc7d..41f05f1 100644
> > > --- a/mm/huge_memory.c
> > > +++ b/mm/huge_memory.c
> > > @@ -726,6 +726,16 @@ int do_huge_pmd_anonymous_page(struct mm_struct *mm, struct vm_area_struct *vma,
> > > return VM_FAULT_OOM;
> > > if (unlikely(khugepaged_enter(vma)))
> > > return VM_FAULT_OOM;
> > > + if (!(flags & FAULT_FLAG_WRITE)) {
> > > + pgtable_t pgtable;
> > > + pgtable = pte_alloc_one(mm, haddr);
> > > + if (unlikely(!pgtable))
> > > + goto out;
> >
> > No use in retrying, just return VM_FAULT_OOM.
>
> Hm. It's consistent with non-hzp path: if pte_alloc_one() in
> __do_huge_pmd_anonymous_page() fails __do_huge_pmd_anonymous_page()
> returns VM_FAULT_OOM which leads to "goto out".
>

If the pte_alloc_one(), which wraps __pte_alloc(), you're adding fails,
it's pointless to "goto out" to try __pte_alloc() which we know won't
succeed.

> Should it be fixed too?
>

It's done for maintainablility because although
__do_huge_pmd_anonymous_page() will only return VM_FAULT_OOM today when
pte_alloc_one() fails, if it were to ever fail in a different way then the
caller is already has a graceful failure.