Commit b676b293 authored Oct 08, 2012 by David Rientjes Committed by Linus Torvalds Oct 09, 2012

mm, thp: fix mapped pages avoiding unevictable list on mlock



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

Signed-off-by: David Rientjes <rientjes@google.com>
Acked-by: Hugh Dickins <hughd@google.com>
Reviewed-by: Andrea Arcangeli <aarcange@redhat.com>
Cc: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michel Lespinasse <walken@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

parent e90bdb7f

include/linux/huge_mm.h

+1 −1

Original line number	Diff line number	Diff line
		@@ -11,7 +11,7 @@ extern int copy_huge_pmd(struct mm_struct dst_mm, struct mm_struct src_mm,
		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 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);

mm/huge_memory.c

+10 −1

Original line number	Diff line number	Diff line
		@@ -971,11 +971,12 @@ out_unlock:
		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);
		@@ -998,6 +999,14 @@ 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)

mm/memory.c

+1 −1

Original line number	Diff line number	Diff line
		@@ -1528,7 +1528,7 @@ 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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