From: "Kirill A. Shutemov" <[email protected]>
Current implementation of huge zero page uses pfn value 0 to indicate that the page hasn't allocated yet. It assumes that buddy page allocator can't return page with pfn == 0. Let's rework the code to store 'struct page *' of huge zero page, not its pfn. This way we can avoid the weak assumption. Signed-off-by: Kirill A. Shutemov <[email protected]> Reported-by: Minchan Kim <[email protected]> Acked-by: Minchan Kim <[email protected]> --- mm/huge_memory.c | 43 +++++++++++++++++++++---------------------- 1 file changed, 21 insertions(+), 22 deletions(-) diff --git a/mm/huge_memory.c b/mm/huge_memory.c index 45eaae0..bc2a548 100644 --- a/mm/huge_memory.c +++ b/mm/huge_memory.c @@ -163,25 +163,24 @@ static int start_khugepaged(void) } static atomic_t huge_zero_refcount; -static unsigned long huge_zero_pfn __read_mostly; +static struct page *huge_zero_page __read_mostly; -static inline bool is_huge_zero_pfn(unsigned long pfn) +static inline bool is_huge_zero_page(struct page *page) { - unsigned long zero_pfn = ACCESS_ONCE(huge_zero_pfn); - return zero_pfn && pfn == zero_pfn; + return ACCESS_ONCE(huge_zero_page) == page; } static inline bool is_huge_zero_pmd(pmd_t pmd) { - return is_huge_zero_pfn(pmd_pfn(pmd)); + return is_huge_zero_page(pmd_page(pmd)); } -static unsigned long get_huge_zero_page(void) +static struct page *get_huge_zero_page(void) { struct page *zero_page; retry: if (likely(atomic_inc_not_zero(&huge_zero_refcount))) - return ACCESS_ONCE(huge_zero_pfn); + return ACCESS_ONCE(huge_zero_page); zero_page = alloc_pages((GFP_TRANSHUGE | __GFP_ZERO) & ~__GFP_MOVABLE, HPAGE_PMD_ORDER); @@ -191,7 +190,7 @@ retry: } count_vm_event(THP_ZERO_PAGE_ALLOC); preempt_disable(); - if (cmpxchg(&huge_zero_pfn, 0, page_to_pfn(zero_page))) { + if (cmpxchg(&huge_zero_page, NULL, zero_page)) { preempt_enable(); __free_page(zero_page); goto retry; @@ -200,7 +199,7 @@ retry: /* We take additional reference here. It will be put back by shrinker */ atomic_set(&huge_zero_refcount, 2); preempt_enable(); - return ACCESS_ONCE(huge_zero_pfn); + return ACCESS_ONCE(huge_zero_page); } static void put_huge_zero_page(void) @@ -220,9 +219,9 @@ static int shrink_huge_zero_page(struct shrinker *shrink, return atomic_read(&huge_zero_refcount) == 1 ? HPAGE_PMD_NR : 0; if (atomic_cmpxchg(&huge_zero_refcount, 1, 0) == 1) { - unsigned long zero_pfn = xchg(&huge_zero_pfn, 0); - BUG_ON(zero_pfn == 0); - __free_page(__pfn_to_page(zero_pfn)); + struct page *zero_page = xchg(&huge_zero_page, NULL); + BUG_ON(zero_page == NULL); + __free_page(zero_page); } return 0; @@ -764,12 +763,12 @@ static inline struct page *alloc_hugepage(int defrag) static bool set_huge_zero_page(pgtable_t pgtable, struct mm_struct *mm, struct vm_area_struct *vma, unsigned long haddr, pmd_t *pmd, - unsigned long zero_pfn) + struct page *zero_page) { pmd_t entry; if (!pmd_none(*pmd)) return false; - entry = pfn_pmd(zero_pfn, vma->vm_page_prot); + entry = mk_pmd(zero_page, vma->vm_page_prot); entry = pmd_wrprotect(entry); entry = pmd_mkhuge(entry); set_pmd_at(mm, haddr, pmd, entry); @@ -794,20 +793,20 @@ int do_huge_pmd_anonymous_page(struct mm_struct *mm, struct vm_area_struct *vma, if (!(flags & FAULT_FLAG_WRITE) && transparent_hugepage_use_zero_page()) { pgtable_t pgtable; - unsigned long zero_pfn; + struct page *zero_page; bool set; pgtable = pte_alloc_one(mm, haddr); if (unlikely(!pgtable)) return VM_FAULT_OOM; - zero_pfn = get_huge_zero_page(); - if (unlikely(!zero_pfn)) { + zero_page = get_huge_zero_page(); + if (unlikely(!zero_page)) { pte_free(mm, pgtable); count_vm_event(THP_FAULT_FALLBACK); goto out; } spin_lock(&mm->page_table_lock); set = set_huge_zero_page(pgtable, mm, vma, haddr, pmd, - zero_pfn); + zero_page); spin_unlock(&mm->page_table_lock); if (!set) { pte_free(mm, pgtable); @@ -886,16 +885,16 @@ int copy_huge_pmd(struct mm_struct *dst_mm, struct mm_struct *src_mm, * a page table. */ if (is_huge_zero_pmd(pmd)) { - unsigned long zero_pfn; + struct page *zero_page; bool set; /* * get_huge_zero_page() will never allocate a new page here, * since we already have a zero page to copy. It just takes a * reference. */ - zero_pfn = get_huge_zero_page(); + zero_page = get_huge_zero_page(); set = set_huge_zero_page(pgtable, dst_mm, vma, addr, dst_pmd, - zero_pfn); + zero_page); BUG_ON(!set); /* unexpected !pmd_none(dst_pmd) */ ret = 0; goto out_unlock; @@ -1803,7 +1802,7 @@ int split_huge_page(struct page *page) struct anon_vma *anon_vma; int ret = 1; - BUG_ON(is_huge_zero_pfn(page_to_pfn(page))); + BUG_ON(is_huge_zero_page(page)); BUG_ON(!PageAnon(page)); /* -- 1.7.10.4 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
