[patch for-3.6] mm, thp: fix mapped pages avoiding unevictable list on mlock

[David Rientjes <rientjes@google.com>]

When a transparent hugepage is mapped and it is included in an mlock()
range, follow_page() incorrectly avoids setting the page's mlock bit and
moving it to the unevictable lru.

This is evident if you try to mlock(), munlock(), and then mlock() a 
range again.  Currently:

	#define MAP_SIZE	(4 << 30)	/* 4GB */

	void *ptr = mmap(NULL, MAP_SIZE, PROT_READ | PROT_WRITE,
			 MAP_PRIVATE | MAP_ANONYMOUS, 0, 0);
	mlock(ptr, MAP_SIZE);

		$ grep -E "Unevictable|Inactive\(anon" /proc/meminfo
		Inactive(anon):     6304 kB
		Unevictable:     4213924 kB

	munlock(ptr, MAP_SIZE);

		Inactive(anon):  4186252 kB
		Unevictable:       19652 kB

	mlock(ptr, MAP_SIZE);

		Inactive(anon):  4198556 kB
		Unevictable:       21684 kB

Notice that less than 2MB was added to the unevictable list; this is
because these pages in the range are not transparent hugepages since the
4GB range was allocated with mmap() and has no specific alignment.  If
posix_memalign() were used instead, unevictable would not have grown at
all on the second mlock().

The fix is to call mlock_vma_page() so that the mlock bit is set and the
page is added to the unevictable list.  With this patch:

	mlock(ptr, MAP_SIZE);

		Inactive(anon):     4056 kB
		Unevictable:     4213940 kB

	munlock(ptr, MAP_SIZE);

		Inactive(anon):  4198268 kB
		Unevictable:       19636 kB

	mlock(ptr, MAP_SIZE);

		Inactive(anon):     4008 kB
		Unevictable:     4213940 kB

Cc: stable@vger.kernel.org [v2.6.38+]
Signed-off-by: David Rientjes <rientjes@google.com>
---
 include/linux/huge_mm.h |    2 +-
 mm/huge_memory.c        |   11 ++++++++++-
 mm/memory.c             |    2 +-
 3 files changed, 12 insertions(+), 3 deletions(-)

diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h
--- a/include/linux/huge_mm.h
+++ b/include/linux/huge_mm.h
@@ -12,7 +12,7 @@ extern int do_huge_pmd_wp_page(struct mm_struct *mm, struct vm_area_struct *vma,
 			       unsigned long address, pmd_t *pmd,
 			       pmd_t orig_pmd);
 extern pgtable_t get_pmd_huge_pte(struct mm_struct *mm);
-extern struct page *follow_trans_huge_pmd(struct mm_struct *mm,
+extern struct page *follow_trans_huge_pmd(struct vm_area_struct *vma,
 					  unsigned long addr,
 					  pmd_t *pmd,
 					  unsigned int flags);
diff --git a/mm/huge_memory.c b/mm/huge_memory.c
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -997,11 +997,12 @@ out:
 	return ret;
 }
 
-struct page *follow_trans_huge_pmd(struct mm_struct *mm,
+struct page *follow_trans_huge_pmd(struct vm_area_struct *vma,
 				   unsigned long addr,
 				   pmd_t *pmd,
 				   unsigned int flags)
 {
+	struct mm_struct *mm = vma->vm_mm;
 	struct page *page = NULL;
 
 	assert_spin_locked(&mm->page_table_lock);
@@ -1024,6 +1025,14 @@ struct page *follow_trans_huge_pmd(struct mm_struct *mm,
 		_pmd = pmd_mkyoung(pmd_mkdirty(*pmd));
 		set_pmd_at(mm, addr & HPAGE_PMD_MASK, pmd, _pmd);
 	}
+	if ((flags & FOLL_MLOCK) && (vma->vm_flags & VM_LOCKED)) {
+		if (page->mapping && trylock_page(page)) {
+			lru_add_drain();
+			if (page->mapping)
+				mlock_vma_page(page);
+			unlock_page(page);
+		}
+	}
 	page += (addr & ~HPAGE_PMD_MASK) >> PAGE_SHIFT;
 	VM_BUG_ON(!PageCompound(page));
 	if (flags & FOLL_GET)
diff --git a/mm/memory.c b/mm/memory.c
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -1521,7 +1521,7 @@ struct page *follow_page(struct vm_area_struct *vma, unsigned long address,
 				spin_unlock(&mm->page_table_lock);
 				wait_split_huge_page(vma->anon_vma, pmd);
 			} else {
-				page = follow_trans_huge_pmd(mm, address,
+				page = follow_trans_huge_pmd(vma, address,
 							     pmd, flags);
 				spin_unlock(&mm->page_table_lock);
 				goto out;

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