From eef1b3ba053aa68967d294c80a50c4a26db30f52 Mon Sep 17 00:00:00 2001 From: "Kirill A. Shutemov" Date: Fri, 15 Jan 2016 16:53:53 -0800 Subject: [PATCH] thp: implement split_huge_pmd() Original split_huge_page() combined two operations: splitting PMDs into tables of PTEs and splitting underlying compound page. This patch implements split_huge_pmd() which split given PMD without splitting other PMDs this page mapped with or underlying compound page. Without tail page refcounting, implementation of split_huge_pmd() is pretty straight-forward. Signed-off-by: Kirill A. Shutemov Tested-by: Sasha Levin Tested-by: Aneesh Kumar K.V Acked-by: Jerome Marchand Cc: Vlastimil Babka Cc: Andrea Arcangeli Cc: Hugh Dickins Cc: Dave Hansen Cc: Mel Gorman Cc: Rik van Riel Cc: Naoya Horiguchi Cc: Steve Capper Cc: Johannes Weiner Cc: Michal Hocko Cc: Christoph Lameter Cc: David Rientjes Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- include/linux/huge_mm.h | 11 +++- mm/huge_memory.c | 124 ++++++++++++++++++++++++++++++++++++++++ 2 files changed, 134 insertions(+), 1 deletion(-) diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h index 333b058b1e3d..f1fa1c283be1 100644 --- a/include/linux/huge_mm.h +++ b/include/linux/huge_mm.h @@ -92,7 +92,16 @@ extern unsigned long transparent_hugepage_flags; #define split_huge_page_to_list(page, list) BUILD_BUG() #define split_huge_page(page) BUILD_BUG() -#define split_huge_pmd(__vma, __pmd, __address) BUILD_BUG() + +void __split_huge_pmd(struct vm_area_struct *vma, pmd_t *pmd, + unsigned long address); + +#define split_huge_pmd(__vma, __pmd, __address) \ + do { \ + pmd_t *____pmd = (__pmd); \ + if (pmd_trans_huge(*____pmd)) \ + __split_huge_pmd(__vma, __pmd, __address); \ + } while (0) #if HPAGE_PMD_ORDER >= MAX_ORDER #error "hugepages can't be allocated by the buddy allocator" diff --git a/mm/huge_memory.c b/mm/huge_memory.c index 1588f688b75d..22ab365cce52 100644 --- a/mm/huge_memory.c +++ b/mm/huge_memory.c @@ -2666,6 +2666,130 @@ static int khugepaged(void *none) return 0; } +static void __split_huge_zero_page_pmd(struct vm_area_struct *vma, + unsigned long haddr, pmd_t *pmd) +{ + struct mm_struct *mm = vma->vm_mm; + pgtable_t pgtable; + pmd_t _pmd; + int i; + + /* leave pmd empty until pte is filled */ + pmdp_huge_clear_flush_notify(vma, haddr, pmd); + + pgtable = pgtable_trans_huge_withdraw(mm, pmd); + pmd_populate(mm, &_pmd, pgtable); + + for (i = 0; i < HPAGE_PMD_NR; i++, haddr += PAGE_SIZE) { + pte_t *pte, entry; + entry = pfn_pte(my_zero_pfn(haddr), vma->vm_page_prot); + entry = pte_mkspecial(entry); + pte = pte_offset_map(&_pmd, haddr); + VM_BUG_ON(!pte_none(*pte)); + set_pte_at(mm, haddr, pte, entry); + pte_unmap(pte); + } + smp_wmb(); /* make pte visible before pmd */ + pmd_populate(mm, pmd, pgtable); + put_huge_zero_page(); +} + +static void __split_huge_pmd_locked(struct vm_area_struct *vma, pmd_t *pmd, + unsigned long haddr) +{ + struct mm_struct *mm = vma->vm_mm; + struct page *page; + pgtable_t pgtable; + pmd_t _pmd; + bool young, write; + int i; + + VM_BUG_ON(haddr & ~HPAGE_PMD_MASK); + VM_BUG_ON_VMA(vma->vm_start > haddr, vma); + VM_BUG_ON_VMA(vma->vm_end < haddr + HPAGE_PMD_SIZE, vma); + VM_BUG_ON(!pmd_trans_huge(*pmd)); + + count_vm_event(THP_SPLIT_PMD); + + if (vma_is_dax(vma)) { + pmd_t _pmd = pmdp_huge_clear_flush_notify(vma, haddr, pmd); + if (is_huge_zero_pmd(_pmd)) + put_huge_zero_page(); + return; + } else if (is_huge_zero_pmd(*pmd)) { + return __split_huge_zero_page_pmd(vma, haddr, pmd); + } + + page = pmd_page(*pmd); + VM_BUG_ON_PAGE(!page_count(page), page); + atomic_add(HPAGE_PMD_NR - 1, &page->_count); + write = pmd_write(*pmd); + young = pmd_young(*pmd); + + /* leave pmd empty until pte is filled */ + pmdp_huge_clear_flush_notify(vma, haddr, pmd); + + pgtable = pgtable_trans_huge_withdraw(mm, pmd); + pmd_populate(mm, &_pmd, pgtable); + + for (i = 0; i < HPAGE_PMD_NR; i++, haddr += PAGE_SIZE) { + pte_t entry, *pte; + /* + * Note that NUMA hinting access restrictions are not + * transferred to avoid any possibility of altering + * permissions across VMAs. + */ + entry = mk_pte(page + i, vma->vm_page_prot); + entry = maybe_mkwrite(pte_mkdirty(entry), vma); + if (!write) + entry = pte_wrprotect(entry); + if (!young) + entry = pte_mkold(entry); + pte = pte_offset_map(&_pmd, haddr); + BUG_ON(!pte_none(*pte)); + set_pte_at(mm, haddr, pte, entry); + atomic_inc(&page[i]._mapcount); + pte_unmap(pte); + } + + /* + * Set PG_double_map before dropping compound_mapcount to avoid + * false-negative page_mapped(). + */ + if (compound_mapcount(page) > 1 && !TestSetPageDoubleMap(page)) { + for (i = 0; i < HPAGE_PMD_NR; i++) + atomic_inc(&page[i]._mapcount); + } + + if (atomic_add_negative(-1, compound_mapcount_ptr(page))) { + /* Last compound_mapcount is gone. */ + __dec_zone_page_state(page, NR_ANON_TRANSPARENT_HUGEPAGES); + if (TestClearPageDoubleMap(page)) { + /* No need in mapcount reference anymore */ + for (i = 0; i < HPAGE_PMD_NR; i++) + atomic_dec(&page[i]._mapcount); + } + } + + smp_wmb(); /* make pte visible before pmd */ + pmd_populate(mm, pmd, pgtable); +} + +void __split_huge_pmd(struct vm_area_struct *vma, pmd_t *pmd, + unsigned long address) +{ + spinlock_t *ptl; + struct mm_struct *mm = vma->vm_mm; + unsigned long haddr = address & HPAGE_PMD_MASK; + + mmu_notifier_invalidate_range_start(mm, haddr, haddr + HPAGE_PMD_SIZE); + ptl = pmd_lock(mm, pmd); + if (likely(pmd_trans_huge(*pmd))) + __split_huge_pmd_locked(vma, pmd, haddr); + spin_unlock(ptl); + mmu_notifier_invalidate_range_end(mm, haddr, haddr + HPAGE_PMD_SIZE); +} + static void split_huge_pmd_address(struct vm_area_struct *vma, unsigned long address) { -- 2.20.1