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Message-Id: <1436550130-112636-30-git-send-email-kirill.shutemov@linux.intel.com>
Date: Fri, 10 Jul 2015 20:42:03 +0300
From: "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
To: Andrew Morton <akpm@...ux-foundation.org>,
Andrea Arcangeli <aarcange@...hat.com>,
Hugh Dickins <hughd@...gle.com>
Cc: Dave Hansen <dave.hansen@...el.com>, Mel Gorman <mgorman@...e.de>,
Rik van Riel <riel@...hat.com>,
Vlastimil Babka <vbabka@...e.cz>,
Christoph Lameter <cl@...two.org>,
Naoya Horiguchi <n-horiguchi@...jp.nec.com>,
Steve Capper <steve.capper@...aro.org>,
"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>,
Johannes Weiner <hannes@...xchg.org>,
Michal Hocko <mhocko@...e.cz>,
Jerome Marchand <jmarchan@...hat.com>,
Sasha Levin <sasha.levin@...cle.com>,
linux-kernel@...r.kernel.org, linux-mm@...ck.org,
"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
Subject: [PATCH 29/36] 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 <kirill.shutemov@...ux.intel.com>
Tested-by: Sasha Levin <sasha.levin@...cle.com>
---
include/linux/huge_mm.h | 11 ++++-
mm/huge_memory.c | 128 ++++++++++++++++++++++++++++++++++++++++++++++++
2 files changed, 138 insertions(+), 1 deletion(-)
diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h
index 67b3f3760f4a..9cfce23ab9d0 100644
--- a/include/linux/huge_mm.h
+++ b/include/linux/huge_mm.h
@@ -94,7 +94,16 @@ 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 5b0a13d2f28c..46daa1dc3dc0 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -2547,6 +2547,134 @@ 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 (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);
+ }
+
+ 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);
+ }
+ } else if (!PageDoubleMap(page)) {
+ /*
+ * The first PMD split for the compound page and we still
+ * have other PMD mapping of the page: bump _mapcount in
+ * every small page.
+ *
+ * This reference will go away with last compound_mapcount.
+ *
+ * Note, we need to increment mapcounts before setting
+ * PG_double_map to avoid false-negative page_mapped().
+ */
+ for (i = 0; i < HPAGE_PMD_NR; i++)
+ atomic_inc(&page[i]._mapcount);
+
+ if (TestSetPageDoubleMap(page)) {
+ /* Race with another __split_huge_pmd() for the page */
+ 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)
{
--
2.1.4
--
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