Messages in this thread | | | Date | Wed, 20 Mar 2013 17:59:53 -0400 | From | Naoya Horiguchi <> | Subject | Re: [PATCH 5/9] migrate: enable migrate_pages() to migrate hugepage |
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On Wed, Mar 20, 2013 at 08:31:06AM +0800, Simon Jeons wrote: ... > >>> diff --git v3.8.orig/mm/mempolicy.c v3.8/mm/mempolicy.c > >>> index e2df1c1..8627135 100644 > >>> --- v3.8.orig/mm/mempolicy.c > >>> +++ v3.8/mm/mempolicy.c > >>> @@ -525,6 +525,27 @@ static int check_pte_range(struct vm_area_struct *vma, pmd_t *pmd, > >>> return addr != end; > >>> } > >>> > >>> +static void check_hugetlb_pmd_range(struct vm_area_struct *vma, pmd_t *pmd, > >>> + const nodemask_t *nodes, unsigned long flags, > >>> + void *private) > >>> +{ > >>> +#ifdef CONFIG_HUGETLB_PAGE > >>> + int nid; > >>> + struct page *page; > >>> + > >>> + spin_lock(&vma->vm_mm->page_table_lock); > >>> + page = pte_page(huge_ptep_get((pte_t *)pmd)); > >>> + spin_unlock(&vma->vm_mm->page_table_lock); > >> I am a bit confused why page_table_lock is used here and why it doesn't > >> cover the page usage. > > I expected this function to do the same for pmd as check_pte_range() does > > for pte, but the above code didn't do it. I should've put spin_unlock > > below migrate_hugepage_add(). Sorry for the confusion. > > I still confuse! Could you explain more in details?
With the above code, check_hugetlb_pmd_range() checks page_mapcount outside the page table lock, but mapcount can be decremented by __unmap_hugepage_range(), so there's a race. __unmap_hugepage_range() calls page_remove_rmap() inside page table lock, so we can avoid this race by doing whole check_hugetlb_pmd_range()'s work inside the page table lock.
Thanks, Naoya
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