[PATCHv9-rebased2,20/37] thp, mlock: do not mlock PTE-mapped file huge pages

Commit Message

Kirill A . Shutemov June 15, 2016, 8:06 p.m. UTC

As with anon THP, we only mlock file huge pages if we can prove that the
page is not mapped with PTE. This way we can avoid mlock leak into
non-mlocked vma on split.

We rely on PageDoubleMap() under lock_page() to check if the the page
may be PTE mapped. PG_double_map is set by page_add_file_rmap() when the
page mapped with PTEs.

Signed-off-by: Kirill A. Shutemov <[e-mail]>
---
 include/linux/page-flags.h | 13 ++++++++++++-
 mm/huge_memory.c           | 27 ++++++++++++++++++++-------
 mm/mmap.c                  |  6 ++++++
 mm/page_alloc.c            |  2 ++
 mm/rmap.c                  | 16 ++++++++++++++--
 5 files changed, 54 insertions(+), 10 deletions(-)

Patch

diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h
index 7c8e82ac2eb7..8cf09639185a 100644
--- a/include/linux/page-flags.h
+++ b/include/linux/page-flags.h
@@ -581,6 +581,17 @@  static inline int PageDoubleMap(struct page *page)
 	return PageHead(page) && test_bit(PG_double_map, &page[1].flags);
 }
 
+static inline void SetPageDoubleMap(struct page *page)
+{
+	VM_BUG_ON_PAGE(!PageHead(page), page);
+	set_bit(PG_double_map, &page[1].flags);
+}
+
+static inline void ClearPageDoubleMap(struct page *page)
+{
+	VM_BUG_ON_PAGE(!PageHead(page), page);
+	clear_bit(PG_double_map, &page[1].flags);
+}
 static inline int TestSetPageDoubleMap(struct page *page)
 {
 	VM_BUG_ON_PAGE(!PageHead(page), page);
@@ -598,7 +609,7 @@  TESTPAGEFLAG_FALSE(TransHuge)
 TESTPAGEFLAG_FALSE(TransCompound)
 TESTPAGEFLAG_FALSE(TransCompoundMap)
 TESTPAGEFLAG_FALSE(TransTail)
-TESTPAGEFLAG_FALSE(DoubleMap)
+PAGEFLAG_FALSE(DoubleMap)
 	TESTSETFLAG_FALSE(DoubleMap)
 	TESTCLEARFLAG_FALSE(DoubleMap)
 #endif
diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 19c2897a607b..6ee521dd0353 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -1436,6 +1436,8 @@  struct page *follow_trans_huge_pmd(struct vm_area_struct *vma,
 		 * We don't mlock() pte-mapped THPs. This way we can avoid
 		 * leaking mlocked pages into non-VM_LOCKED VMAs.
 		 *
+		 * For anon THP:
+		 *
 		 * In most cases the pmd is the only mapping of the page as we
 		 * break COW for the mlock() -- see gup_flags |= FOLL_WRITE for
 		 * writable private mappings in populate_vma_page_range().
@@ -1443,15 +1445,26 @@  struct page *follow_trans_huge_pmd(struct vm_area_struct *vma,
 		 * The only scenario when we have the page shared here is if we
 		 * mlocking read-only mapping shared over fork(). We skip
 		 * mlocking such pages.
+		 *
+		 * For file THP:
+		 *
+		 * We can expect PageDoubleMap() to be stable under page lock:
+		 * for file pages we set it in page_add_file_rmap(), which
+		 * requires page to be locked.
 		 */
-		if (compound_mapcount(page) == 1 && !PageDoubleMap(page) &&
-				page->mapping && trylock_page(page)) {
-			lru_add_drain();
-			if (page->mapping)
-				mlock_vma_page(page);
-			unlock_page(page);
-		}
+
+		if (PageAnon(page) && compound_mapcount(page) != 1)
+			goto skip_mlock;
+		if (PageDoubleMap(page) || !page->mapping)
+			goto skip_mlock;
+		if (!trylock_page(page))
+			goto skip_mlock;
+		lru_add_drain();
+		if (page->mapping && !PageDoubleMap(page))
+			mlock_vma_page(page);
+		unlock_page(page);
 	}
+skip_mlock:
 	page += (addr & ~HPAGE_PMD_MASK) >> PAGE_SHIFT;
 	VM_BUG_ON_PAGE(!PageCompound(page), page);
 	if (flags & FOLL_GET)
diff --git a/mm/mmap.c b/mm/mmap.c
index 02990e7dd70e..daabef097c78 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -2591,6 +2591,12 @@  SYSCALL_DEFINE5(remap_file_pages, unsigned long, start, unsigned long, size,
 		/* drop PG_Mlocked flag for over-mapped range */
 		for (tmp = vma; tmp->vm_start >= start + size;
 				tmp = tmp->vm_next) {
+			/*
+			 * Split pmd and munlock page on the border
+			 * of the range.
+			 */
+			vma_adjust_trans_huge(tmp, start, start + size, 0);
+
 			munlock_vma_pages_range(tmp,
 					max(tmp->vm_start, start),
 					min(tmp->vm_end, start + size));
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 180f5afc5a1f..d35a907d7a07 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -1005,6 +1005,8 @@  static __always_inline bool free_pages_prepare(struct page *page,
 
 		VM_BUG_ON_PAGE(compound && compound_order(page) != order, page);
 
+		if (compound)
+			ClearPageDoubleMap(page);
 		for (i = 1; i < (1 << order); i++) {
 			if (compound)
 				bad += free_tail_pages_check(page, page + i);
diff --git a/mm/rmap.c b/mm/rmap.c
index b78374519bac..26e3e784ad75 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -1287,6 +1287,12 @@  void page_add_file_rmap(struct page *page, bool compound)
 		if (!atomic_inc_and_test(compound_mapcount_ptr(page)))
 			goto out;
 	} else {
+		if (PageTransCompound(page)) {
+			VM_BUG_ON_PAGE(!PageLocked(page), page);
+			SetPageDoubleMap(compound_head(page));
+			if (PageMlocked(page))
+				clear_page_mlock(compound_head(page));
+		}
 		if (!atomic_inc_and_test(&page->_mapcount))
 			goto out;
 	}
@@ -1460,8 +1466,14 @@  static int try_to_unmap_one(struct page *page, struct vm_area_struct *vma,
 	 */
 	if (!(flags & TTU_IGNORE_MLOCK)) {
 		if (vma->vm_flags & VM_LOCKED) {
-			/* Holding pte lock, we do *not* need mmap_sem here */
-			mlock_vma_page(page);
+			/* PTE-mapped THP are never mlocked */
+			if (!PageTransCompound(page)) {
+				/*
+				 * Holding pte lock, we do *not* need
+				 * mmap_sem here
+				 */
+				mlock_vma_page(page);
+			}
 			ret = SWAP_MLOCK;
 			goto out_unmap;
 		}