On Wed, Nov 19, 2014 at 09:02:42AM +0000, Naoya Horiguchi wrote:
> On Wed, Nov 05, 2014 at 04:49:52PM +0200, Kirill A. Shutemov wrote:
> > We don't yet handle mlocked pages properly with new THP refcounting.
> > For now we split all pages in VMA on mlock and disallow khugepaged
> > collapse pages in the VMA. If split failed on mlock() we fail the
> > syscall with -EBUSY.
> > ---
> ...
>
> > @@ -542,6 +530,60 @@ next:
> > }
> > }
> >
> > +static int thp_split(pmd_t *pmd, unsigned long addr, unsigned long end,
> > + struct mm_walk *walk)
> > +{
> > + spinlock_t *ptl;
> > + struct page *page = NULL;
> > + pte_t *pte;
> > + int err = 0;
> > +
> > +retry:
> > + if (pmd_none(*pmd))
> > + return 0;
> > + if (pmd_trans_huge(*pmd)) {
> > + if (is_huge_zero_pmd(*pmd)) {
> > + split_huge_pmd(walk->vma, pmd, addr);
> > + return 0;
> > + }
> > + ptl = pmd_lock(walk->mm, pmd);
> > + if (!pmd_trans_huge(*pmd)) {
> > + spin_unlock(ptl);
> > + goto retry;
> > + }
> > + page = pmd_page(*pmd);
> > + VM_BUG_ON_PAGE(!PageHead(page), page);
> > + get_page(page);
> > + spin_unlock(ptl);
> > + err = split_huge_page(page);
> > + put_page(page);
> > + return err;
> > + }
> > + pte = pte_offset_map_lock(walk->mm, pmd, addr, &ptl);
> > + do {
> > + if (!pte_present(*pte))
> > + continue;
> > + page = vm_normal_page(walk->vma, addr, *pte);
> > + if (!page)
> > + continue;
> > + if (PageTransCompound(page)) {
> > + page = compound_head(page);
> > + get_page(page);
> > + spin_unlock(ptl);
> > + err = split_huge_page(page);
> > + spin_lock(ptl);
> > + put_page(page);
> > + if (!err) {
> > + VM_BUG_ON_PAGE(compound_mapcount(page), page);
> > + VM_BUG_ON_PAGE(PageTransCompound(page), page);
>
> If split_huge_page() succeeded, we don't have to continue the iteration,
> so break this loop here?
We may want to skip to the next huge page region, but the patch is crap
anyway -- don't bother.
--
Kirill A. Shutemov
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