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[PATCHv3 16/29] thp: skip file huge pmd on copy_huge_pmd()

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copy_page_range() has a check for "Don't copy ptes where a page fault
will fill them correctly." It works on VMA level. We still copy all page
table entries from private mappings, even if they map page cache.

We can simplify copy_huge_pmd() a bit by skipping file PMDs.

We don't map file private pages with PMDs, so they only can map page
cache. It's safe to skip them as they can be re-faulted later.

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
---
 mm/huge_memory.c | 34 ++++++++++++++++------------------
 1 file changed, 16 insertions(+), 18 deletions(-)

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 985041c453bf..c0ffa6a7803a 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -1052,14 +1052,15 @@ int copy_huge_pmd(struct mm_struct *dst_mm, struct mm_struct *src_mm,
 	struct page *src_page;
 	pmd_t pmd;
 	pgtable_t pgtable = NULL;
-	int ret;
+	int ret = -ENOMEM;
 
-	if (!vma_is_dax(vma)) {
-		ret = -ENOMEM;
-		pgtable = pte_alloc_one(dst_mm, addr);
-		if (unlikely(!pgtable))
-			goto out;
-	}
+	/* Skip if can be re-fill on fault */
+	if (!vma_is_anonymous(vma))
+		return 0;
+
+	pgtable = pte_alloc_one(dst_mm, addr);
+	if (unlikely(!pgtable))
+		goto out;
 
 	dst_ptl = pmd_lock(dst_mm, dst_pmd);
 	src_ptl = pmd_lockptr(src_mm, src_pmd);
@@ -1067,7 +1068,7 @@ int copy_huge_pmd(struct mm_struct *dst_mm, struct mm_struct *src_mm,
 
 	ret = -EAGAIN;
 	pmd = *src_pmd;
-	if (unlikely(!pmd_trans_huge(pmd) && !pmd_devmap(pmd))) {
+	if (unlikely(!pmd_trans_huge(pmd))) {
 		pte_free(dst_mm, pgtable);
 		goto out_unlock;
 	}
@@ -1090,16 +1091,13 @@ int copy_huge_pmd(struct mm_struct *dst_mm, struct mm_struct *src_mm,
 		goto out_unlock;
 	}
 
-	if (!vma_is_dax(vma)) {
-		/* thp accounting separate from pmd_devmap accounting */
-		src_page = pmd_page(pmd);
-		VM_BUG_ON_PAGE(!PageHead(src_page), src_page);
-		get_page(src_page);
-		page_dup_rmap(src_page, true);
-		add_mm_counter(dst_mm, MM_ANONPAGES, HPAGE_PMD_NR);
-		atomic_long_inc(&dst_mm->nr_ptes);
-		pgtable_trans_huge_deposit(dst_mm, dst_pmd, pgtable);
-	}
+	src_page = pmd_page(pmd);
+	VM_BUG_ON_PAGE(!PageHead(src_page), src_page);
+	get_page(src_page);
+	page_dup_rmap(src_page, true);
+	add_mm_counter(dst_mm, MM_ANONPAGES, HPAGE_PMD_NR);
+	atomic_long_inc(&dst_mm->nr_ptes);
+	pgtable_trans_huge_deposit(dst_mm, dst_pmd, pgtable);
 
 	pmdp_set_wrprotect(src_mm, addr, src_pmd);
 	pmd = pmd_mkold(pmd_wrprotect(pmd));
-- 
2.7.0

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[PATCHv3 00/29] huge tmpfs implementation using compound pages "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> - 2016-03-03 18:10 +0100
  [PATCHv3 25/29] truncate: handle file thp "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> - 2016-03-03 18:10 +0100
  [PATCHv3 05/29] mm: do not pass mm_struct into handle_mm_fault "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> - 2016-03-03 18:10 +0100
  [PATCHv3 12/29] thp: support file pages in zap_huge_pmd() "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> - 2016-03-03 18:10 +0100
  [PATCHv3 18/29] thp: run vma_adjust_trans_huge() outside i_mmap_rwsem "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> - 2016-03-03 18:10 +0100
  [PATCHv3 29/29] shmem, thp: respect MADV_{NO,}HUGEPAGE for file mappings "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> - 2016-03-03 18:10 +0100
  [PATCHv3 03/29] mm: make remove_migration_ptes() beyond mm/migration.c "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> - 2016-03-03 18:10 +0100
  [PATCHv3 14/29] thp: handle file COW faults "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> - 2016-03-03 18:10 +0100
  [PATCHv3 02/29] rmap: extend try_to_unmap() to be usable by split_huge_page() "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> - 2016-03-03 18:10 +0100
  [PATCHv3 01/29] rmap: introduce rmap_walk_locked() "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> - 2016-03-03 18:10 +0100
  [PATCHv3 07/29] mm: postpone page table allocation until we have page to map "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> - 2016-03-03 18:10 +0100
  [PATCHv3 13/29] thp: handle file pages in split_huge_pmd() "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> - 2016-03-03 18:10 +0100
  [PATCHv3 15/29] thp: handle file pages in mremap() "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> - 2016-03-03 18:10 +0100
  [PATCHv3 20/29] thp, mlock: do not mlock PTE-mapped file huge pages "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> - 2016-03-03 18:10 +0100
  [PATCHv3 08/29] rmap: support file thp "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> - 2016-03-03 18:10 +0100
  [PATCHv3 16/29] thp: skip file huge pmd on copy_huge_pmd() "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> - 2016-03-03 18:10 +0100
  [PATCHv3 22/29] page-flags: relax policy for PG_mappedtodisk and PG_reclaim "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> - 2016-03-03 18:10 +0100
  Re: [PATCHv3 00/29] huge tmpfs implementation using compound pages Sasha Levin <sasha.levin@oracle.com> - 2016-03-04 05:30 +0100

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