mlock: mlocked pages are unevictable

Make sure that mlocked pages also live on the unevictable LRU, so kswapd
will not scan them over and over again.

This is achieved through various strategies:

1) add yet another page flag--PG_mlocked--to indicate that
the page is locked for efficient testing in vmscan and,
optionally, fault path. This allows early culling of
unevictable pages, preventing them from getting to
page_referenced()/try_to_unmap(). Also allows separate
accounting of mlock'd pages, as Nick's original patch
did.

Note: Nick's original mlock patch used a PG_mlocked
flag. I had removed this in favor of the PG_unevictable
flag + an mlock_count [new page struct member]. I
restored the PG_mlocked flag to eliminate the new
count field.

2) add the mlock/unevictable infrastructure to mm/mlock.c,
with internal APIs in mm/internal.h. This is a rework
of Nick's original patch to these files, taking into
account that mlocked pages are now kept on unevictable
LRU list.

3) update vmscan.c:page_evictable() to check PageMlocked()
and, if vma passed in, the vm_flags. Note that the vma
will only be passed in for new pages in the fault path;
and then only if the "cull unevictable pages in fault
path" patch is included.

4) add try_to_unlock() to rmap.c to walk a page's rmap and
ClearPageMlocked() if no other vmas have it mlocked.
Reuses as much of try_to_unmap() as possible. This
effectively replaces the use of one of the lru list links
as an mlock count. If this mechanism let's pages in mlocked
vmas leak through w/o PG_mlocked set [I don't know that it
does], we should catch them later in try_to_unmap(). One
hopes this will be rare, as it will be relatively expensive.

Original mm/internal.h, mm/rmap.c and mm/mlock.c changes:
Signed-off-by: Nick Piggin <[e-mail]>

splitlru: introduce __get_user_pages():

New munlock processing need to GUP_FLAGS_IGNORE_VMA_PERMISSIONS.
because current get_user_pages() can't grab PROT_NONE pages theresore it
cause PROT_NONE pages can't munlock.

[[e-mail]: fix this for pagemap-pass-mm-into-pagewalkers.patch]
[[e-mail]: untangle patch interdependencies]
[[e-mail]: fix things after out-of-order merging]
[[e-mail]: fix page-flags mess]
[[e-mail]: fix munlock page table walk - now requires 'mm']
[[e-mail]: build fix]
[[e-mail]: fix truncate race and sevaral comments]
[[e-mail]: splitlru: introduce __get_user_pages()]
Signed-off-by: KOSAKI Motohiro <[e-mail]>
Signed-off-by: Rik van Riel <[e-mail]>
Signed-off-by: Lee Schermerhorn <[e-mail]>
Cc: Nick Piggin <[e-mail]>
Cc: Dave Hansen <[e-mail]>
Cc: Matt Mackall <[e-mail]>
Signed-off-by: Hugh Dickins <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

include/linux/mm.h

···
 #define VM_RandomReadHint(v)		((v)->vm_flags & VM_RAND_READ)
 
 /*
+ * special vmas that are non-mergable, non-mlock()able
+ */
+#define VM_SPECIAL (VM_IO | VM_DONTEXPAND | VM_RESERVED | VM_PFNMAP)
+
+/*
  * mapping from the currently active vm_flags protection bits (the
  * low four bits) to a page protection mask..
  */

include/linux/page-flags.h

···
 	PG_swapbacked,		/* Page is backed by RAM/swap */
 #ifdef CONFIG_UNEVICTABLE_LRU
 	PG_unevictable,		/* Page is "unevictable"  */
+	PG_mlocked,		/* Page is vma mlocked */
 #endif
 #ifdef CONFIG_IA64_UNCACHED_ALLOCATOR
 	PG_uncached,		/* Page has been mapped as uncached */
···
 #ifdef CONFIG_UNEVICTABLE_LRU
 PAGEFLAG(Unevictable, unevictable) __CLEARPAGEFLAG(Unevictable, unevictable)
 	TESTCLEARFLAG(Unevictable, unevictable)
+
+#define MLOCK_PAGES 1
+PAGEFLAG(Mlocked, mlocked) __CLEARPAGEFLAG(Mlocked, mlocked)
+	TESTSCFLAG(Mlocked, mlocked)
+
 #else
+
+#define MLOCK_PAGES 0
+PAGEFLAG_FALSE(Mlocked)
+	SETPAGEFLAG_NOOP(Mlocked) TESTCLEARFLAG_FALSE(Mlocked)
+
 PAGEFLAG_FALSE(Unevictable) TESTCLEARFLAG_FALSE(Unevictable)
 	SETPAGEFLAG_NOOP(Unevictable) CLEARPAGEFLAG_NOOP(Unevictable)
 	__CLEARPAGEFLAG_NOOP(Unevictable)
···
 #endif /* !PAGEFLAGS_EXTENDED */
 
 #ifdef CONFIG_UNEVICTABLE_LRU
-#define __PG_UNEVICTABLE (1 << PG_unevictable)
+#define __PG_UNEVICTABLE	(1 << PG_unevictable)
+#define __PG_MLOCKED		(1 << PG_mlocked)
 #else
-#define __PG_UNEVICTABLE 0
+#define __PG_UNEVICTABLE	0
+#define __PG_MLOCKED		0
 #endif
 
 #define PAGE_FLAGS	(1 << PG_lru   | 1 << PG_private   | 1 << PG_locked | \
 			 1 << PG_buddy | 1 << PG_writeback | \
 			 1 << PG_slab  | 1 << PG_swapcache | 1 << PG_active | \
-			 __PG_UNEVICTABLE)
+			 __PG_UNEVICTABLE | __PG_MLOCKED)
 
 /*
  * Flags checked in bad_page().  Pages on the free list should not have

include/linux/rmap.h

···
  */
 int page_mkclean(struct page *);
 
+#ifdef CONFIG_UNEVICTABLE_LRU
+/*
+ * called in munlock()/munmap() path to check for other vmas holding
+ * the page mlocked.
+ */
+int try_to_munlock(struct page *);
+#else
+static inline int try_to_munlock(struct page *page)
+{
+	return 0;	/* a.k.a. SWAP_SUCCESS */
+}
+#endif
+
 #else	/* !CONFIG_MMU */
 
 #define anon_vma_init()		do {} while (0)
···
 #define SWAP_SUCCESS	0
 #define SWAP_AGAIN	1
 #define SWAP_FAIL	2
+#define SWAP_MLOCK	3
 
 #endif	/* _LINUX_RMAP_H */

mm/internal.h

···
 	return page_private(page);
 }
 
+extern int mlock_vma_pages_range(struct vm_area_struct *vma,
+			unsigned long start, unsigned long end);
+extern void munlock_vma_pages_all(struct vm_area_struct *vma);
+
 #ifdef CONFIG_UNEVICTABLE_LRU
 /*
  * unevictable_migrate_page() called only from migrate_page_copy() to
···
 }
 #endif
 
+#ifdef CONFIG_UNEVICTABLE_LRU
+/*
+ * Called only in fault path via page_evictable() for a new page
+ * to determine if it's being mapped into a LOCKED vma.
+ * If so, mark page as mlocked.
+ */
+static inline int is_mlocked_vma(struct vm_area_struct *vma, struct page *page)
+{
+	VM_BUG_ON(PageLRU(page));
+
+	if (likely((vma->vm_flags & (VM_LOCKED | VM_SPECIAL)) != VM_LOCKED))
+		return 0;
+
+	SetPageMlocked(page);
+	return 1;
+}
+
+/*
+ * must be called with vma's mmap_sem held for read, and page locked.
+ */
+extern void mlock_vma_page(struct page *page);
+
+/*
+ * Clear the page's PageMlocked().  This can be useful in a situation where
+ * we want to unconditionally remove a page from the pagecache -- e.g.,
+ * on truncation or freeing.
+ *
+ * It is legal to call this function for any page, mlocked or not.
+ * If called for a page that is still mapped by mlocked vmas, all we do
+ * is revert to lazy LRU behaviour -- semantics are not broken.
+ */
+extern void __clear_page_mlock(struct page *page);
+static inline void clear_page_mlock(struct page *page)
+{
+	if (unlikely(TestClearPageMlocked(page)))
+		__clear_page_mlock(page);
+}
+
+/*
+ * mlock_migrate_page - called only from migrate_page_copy() to
+ * migrate the Mlocked page flag
+ */
+static inline void mlock_migrate_page(struct page *newpage, struct page *page)
+{
+	if (TestClearPageMlocked(page))
+		SetPageMlocked(newpage);
+}
+
+
+#else /* CONFIG_UNEVICTABLE_LRU */
+static inline int is_mlocked_vma(struct vm_area_struct *v, struct page *p)
+{
+	return 0;
+}
+static inline void clear_page_mlock(struct page *page) { }
+static inline void mlock_vma_page(struct page *page) { }
+static inline void mlock_migrate_page(struct page *new, struct page *old) { }
+
+#endif /* CONFIG_UNEVICTABLE_LRU */
 
 /*
  * FLATMEM and DISCONTIGMEM configurations use alloc_bootmem_node,
···
 {
 }
 #endif /* CONFIG_SPARSEMEM */
+
+#define GUP_FLAGS_WRITE                  0x1
+#define GUP_FLAGS_FORCE                  0x2
+#define GUP_FLAGS_IGNORE_VMA_PERMISSIONS 0x4
+
+int __get_user_pages(struct task_struct *tsk, struct mm_struct *mm,
+		     unsigned long start, int len, int flags,
+		     struct page **pages, struct vm_area_struct **vmas);
 
 #endif

mm/memory.c

···
 
 #include "internal.h"
 
+#include "internal.h"
+
 #ifndef CONFIG_NEED_MULTIPLE_NODES
 /* use the per-pgdat data instead for discontigmem - mbligh */
 unsigned long max_mapnr;
···
 	return !vma->vm_ops || !vma->vm_ops->fault;
 }
 
-int get_user_pages(struct task_struct *tsk, struct mm_struct *mm,
-		unsigned long start, int len, int write, int force,
+
+
+int __get_user_pages(struct task_struct *tsk, struct mm_struct *mm,
+		     unsigned long start, int len, int flags,
 		struct page **pages, struct vm_area_struct **vmas)
 {
 	int i;
-	unsigned int vm_flags;
+	unsigned int vm_flags = 0;
+	int write = !!(flags & GUP_FLAGS_WRITE);
+	int force = !!(flags & GUP_FLAGS_FORCE);
+	int ignore = !!(flags & GUP_FLAGS_IGNORE_VMA_PERMISSIONS);
 
 	if (len <= 0)
 		return 0;
···
 			pud_t *pud;
 			pmd_t *pmd;
 			pte_t *pte;
-			if (write) /* user gate pages are read-only */
+
+			/* user gate pages are read-only */
+			if (!ignore && write)
 				return i ? : -EFAULT;
 			if (pg > TASK_SIZE)
 				pgd = pgd_offset_k(pg);
···
 			continue;
 		}
 
-		if (!vma || (vma->vm_flags & (VM_IO | VM_PFNMAP))
-				|| !(vm_flags & vma->vm_flags))
+		if (!vma ||
+		    (vma->vm_flags & (VM_IO | VM_PFNMAP)) ||
+		    (!ignore && !(vm_flags & vma->vm_flags)))
 			return i ? : -EFAULT;
 
 		if (is_vm_hugetlb_page(vma)) {
···
 	} while (len);
 	return i;
 }
+
+int get_user_pages(struct task_struct *tsk, struct mm_struct *mm,
+		unsigned long start, int len, int write, int force,
+		struct page **pages, struct vm_area_struct **vmas)
+{
+	int flags = 0;
+
+	if (write)
+		flags |= GUP_FLAGS_WRITE;
+	if (force)
+		flags |= GUP_FLAGS_FORCE;
+
+	return __get_user_pages(tsk, mm,
+				start, len, flags,
+				pages, vmas);
+}
+
 EXPORT_SYMBOL(get_user_pages);
 
 pte_t *get_locked_pte(struct mm_struct *mm, unsigned long addr,
···
 	new_page = alloc_page_vma(GFP_HIGHUSER_MOVABLE, vma, address);
 	if (!new_page)
 		goto oom;
+	/*
+	 * Don't let another task, with possibly unlocked vma,
+	 * keep the mlocked page.
+	 */
+	if (vma->vm_flags & VM_LOCKED) {
+		lock_page(old_page);	/* for LRU manipulation */
+		clear_page_mlock(old_page);
+		unlock_page(old_page);
+	}
 	cow_user_page(new_page, old_page, address, vma);
 	__SetPageUptodate(new_page);
 
···
 	page_add_anon_rmap(page, vma, address);
 
 	swap_free(entry);
-	if (vm_swap_full())
+	if (vm_swap_full() || (vma->vm_flags & VM_LOCKED) || PageMlocked(page))
 		remove_exclusive_swap_page(page);
 	unlock_page(page);
 
···
 				ret = VM_FAULT_OOM;
 				goto out;
 			}
+			/*
+			 * Don't let another task, with possibly unlocked vma,
+			 * keep the mlocked page.
+			 */
+			if (vma->vm_flags & VM_LOCKED)
+				clear_page_mlock(vmf.page);
 			copy_user_highpage(page, vmf.page, address, vma);
 			__SetPageUptodate(page);
 		} else {

mm/migrate.c

···
 		__set_page_dirty_nobuffers(newpage);
  	}
 
+	mlock_migrate_page(newpage, page);
+
 #ifdef CONFIG_SWAP
 	ClearPageSwapCache(page);
 #endif

mm/mlock.c

···
 #include <linux/capability.h>
 #include <linux/mman.h>
 #include <linux/mm.h>
+#include <linux/swap.h>
+#include <linux/swapops.h>
+#include <linux/pagemap.h>
 #include <linux/mempolicy.h>
 #include <linux/syscalls.h>
 #include <linux/sched.h>
 #include <linux/module.h>
+#include <linux/rmap.h>
+#include <linux/mmzone.h>
+#include <linux/hugetlb.h>
+
+#include "internal.h"
 
 int can_do_mlock(void)
 {
···
 }
 EXPORT_SYMBOL(can_do_mlock);
 
+#ifdef CONFIG_UNEVICTABLE_LRU
+/*
+ * Mlocked pages are marked with PageMlocked() flag for efficient testing
+ * in vmscan and, possibly, the fault path; and to support semi-accurate
+ * statistics.
+ *
+ * An mlocked page [PageMlocked(page)] is unevictable.  As such, it will
+ * be placed on the LRU "unevictable" list, rather than the [in]active lists.
+ * The unevictable list is an LRU sibling list to the [in]active lists.
+ * PageUnevictable is set to indicate the unevictable state.
+ *
+ * When lazy mlocking via vmscan, it is important to ensure that the
+ * vma's VM_LOCKED status is not concurrently being modified, otherwise we
+ * may have mlocked a page that is being munlocked. So lazy mlock must take
+ * the mmap_sem for read, and verify that the vma really is locked
+ * (see mm/rmap.c).
+ */
+
+/*
+ *  LRU accounting for clear_page_mlock()
+ */
+void __clear_page_mlock(struct page *page)
+{
+	VM_BUG_ON(!PageLocked(page));
+
+	if (!page->mapping) {	/* truncated ? */
+		return;
+	}
+
+	if (!isolate_lru_page(page)) {
+		putback_lru_page(page);
+	} else {
+		/*
+		 * Page not on the LRU yet.  Flush all pagevecs and retry.
+		 */
+		lru_add_drain_all();
+		if (!isolate_lru_page(page))
+			putback_lru_page(page);
+	}
+}
+
+/*
+ * Mark page as mlocked if not already.
+ * If page on LRU, isolate and putback to move to unevictable list.
+ */
+void mlock_vma_page(struct page *page)
+{
+	BUG_ON(!PageLocked(page));
+
+	if (!TestSetPageMlocked(page) && !isolate_lru_page(page))
+		putback_lru_page(page);
+}
+
+/*
+ * called from munlock()/munmap() path with page supposedly on the LRU.
+ *
+ * Note:  unlike mlock_vma_page(), we can't just clear the PageMlocked
+ * [in try_to_munlock()] and then attempt to isolate the page.  We must
+ * isolate the page to keep others from messing with its unevictable
+ * and mlocked state while trying to munlock.  However, we pre-clear the
+ * mlocked state anyway as we might lose the isolation race and we might
+ * not get another chance to clear PageMlocked.  If we successfully
+ * isolate the page and try_to_munlock() detects other VM_LOCKED vmas
+ * mapping the page, it will restore the PageMlocked state, unless the page
+ * is mapped in a non-linear vma.  So, we go ahead and SetPageMlocked(),
+ * perhaps redundantly.
+ * If we lose the isolation race, and the page is mapped by other VM_LOCKED
+ * vmas, we'll detect this in vmscan--via try_to_munlock() or try_to_unmap()
+ * either of which will restore the PageMlocked state by calling
+ * mlock_vma_page() above, if it can grab the vma's mmap sem.
+ */
+static void munlock_vma_page(struct page *page)
+{
+	BUG_ON(!PageLocked(page));
+
+	if (TestClearPageMlocked(page) && !isolate_lru_page(page)) {
+		try_to_munlock(page);
+		putback_lru_page(page);
+	}
+}
+
+/*
+ * mlock a range of pages in the vma.
+ *
+ * This takes care of making the pages present too.
+ *
+ * vma->vm_mm->mmap_sem must be held for write.
+ */
+static int __mlock_vma_pages_range(struct vm_area_struct *vma,
+			unsigned long start, unsigned long end)
+{
+	struct mm_struct *mm = vma->vm_mm;
+	unsigned long addr = start;
+	struct page *pages[16]; /* 16 gives a reasonable batch */
+	int write = !!(vma->vm_flags & VM_WRITE);
+	int nr_pages = (end - start) / PAGE_SIZE;
+	int ret;
+
+	VM_BUG_ON(start & ~PAGE_MASK || end & ~PAGE_MASK);
+	VM_BUG_ON(start < vma->vm_start || end > vma->vm_end);
+	VM_BUG_ON(!rwsem_is_locked(&vma->vm_mm->mmap_sem));
+
+	lru_add_drain_all();	/* push cached pages to LRU */
+
+	while (nr_pages > 0) {
+		int i;
+
+		cond_resched();
+
+		/*
+		 * get_user_pages makes pages present if we are
+		 * setting mlock. and this extra reference count will
+		 * disable migration of this page.  However, page may
+		 * still be truncated out from under us.
+		 */
+		ret = get_user_pages(current, mm, addr,
+				min_t(int, nr_pages, ARRAY_SIZE(pages)),
+				write, 0, pages, NULL);
+		/*
+		 * This can happen for, e.g., VM_NONLINEAR regions before
+		 * a page has been allocated and mapped at a given offset,
+		 * or for addresses that map beyond end of a file.
+		 * We'll mlock the the pages if/when they get faulted in.
+		 */
+		if (ret < 0)
+			break;
+		if (ret == 0) {
+			/*
+			 * We know the vma is there, so the only time
+			 * we cannot get a single page should be an
+			 * error (ret < 0) case.
+			 */
+			WARN_ON(1);
+			break;
+		}
+
+		lru_add_drain();	/* push cached pages to LRU */
+
+		for (i = 0; i < ret; i++) {
+			struct page *page = pages[i];
+
+			lock_page(page);
+			/*
+			 * Because we lock page here and migration is blocked
+			 * by the elevated reference, we need only check for
+			 * page truncation (file-cache only).
+			 */
+			if (page->mapping)
+				mlock_vma_page(page);
+			unlock_page(page);
+			put_page(page);		/* ref from get_user_pages() */
+
+			/*
+			 * here we assume that get_user_pages() has given us
+			 * a list of virtually contiguous pages.
+			 */
+			addr += PAGE_SIZE;	/* for next get_user_pages() */
+			nr_pages--;
+		}
+	}
+
+	lru_add_drain_all();	/* to update stats */
+
+	return 0;	/* count entire vma as locked_vm */
+}
+
+/*
+ * private structure for munlock page table walk
+ */
+struct munlock_page_walk {
+	struct vm_area_struct *vma;
+	pmd_t                 *pmd; /* for migration_entry_wait() */
+};
+
+/*
+ * munlock normal pages for present ptes
+ */
+static int __munlock_pte_handler(pte_t *ptep, unsigned long addr,
+				   unsigned long end, struct mm_walk *walk)
+{
+	struct munlock_page_walk *mpw = walk->private;
+	swp_entry_t entry;
+	struct page *page;
+	pte_t pte;
+
+retry:
+	pte = *ptep;
+	/*
+	 * If it's a swap pte, we might be racing with page migration.
+	 */
+	if (unlikely(!pte_present(pte))) {
+		if (!is_swap_pte(pte))
+			goto out;
+		entry = pte_to_swp_entry(pte);
+		if (is_migration_entry(entry)) {
+			migration_entry_wait(mpw->vma->vm_mm, mpw->pmd, addr);
+			goto retry;
+		}
+		goto out;
+	}
+
+	page = vm_normal_page(mpw->vma, addr, pte);
+	if (!page)
+		goto out;
+
+	lock_page(page);
+	if (!page->mapping) {
+		unlock_page(page);
+		goto retry;
+	}
+	munlock_vma_page(page);
+	unlock_page(page);
+
+out:
+	return 0;
+}
+
+/*
+ * Save pmd for pte handler for waiting on migration entries
+ */
+static int __munlock_pmd_handler(pmd_t *pmd, unsigned long addr,
+				 unsigned long end, struct mm_walk *walk)
+{
+	struct munlock_page_walk *mpw = walk->private;
+
+	mpw->pmd = pmd;
+	return 0;
+}
+
+
+/*
+ * munlock a range of pages in the vma using standard page table walk.
+ *
+ * vma->vm_mm->mmap_sem must be held for write.
+ */
+static void __munlock_vma_pages_range(struct vm_area_struct *vma,
+			      unsigned long start, unsigned long end)
+{
+	struct mm_struct *mm = vma->vm_mm;
+	struct munlock_page_walk mpw = {
+		.vma = vma,
+	};
+	struct mm_walk munlock_page_walk = {
+		.pmd_entry = __munlock_pmd_handler,
+		.pte_entry = __munlock_pte_handler,
+		.private = &mpw,
+		.mm = mm,
+	};
+
+	VM_BUG_ON(start & ~PAGE_MASK || end & ~PAGE_MASK);
+	VM_BUG_ON(!rwsem_is_locked(&vma->vm_mm->mmap_sem));
+	VM_BUG_ON(start < vma->vm_start);
+	VM_BUG_ON(end > vma->vm_end);
+
+	lru_add_drain_all();	/* push cached pages to LRU */
+	walk_page_range(start, end, &munlock_page_walk);
+	lru_add_drain_all();	/* to update stats */
+}
+
+#else /* CONFIG_UNEVICTABLE_LRU */
+
+/*
+ * Just make pages present if VM_LOCKED.  No-op if unlocking.
+ */
+static int __mlock_vma_pages_range(struct vm_area_struct *vma,
+			unsigned long start, unsigned long end)
+{
+	if (vma->vm_flags & VM_LOCKED)
+		make_pages_present(start, end);
+	return 0;
+}
+
+/*
+ * munlock a range of pages in the vma -- no-op.
+ */
+static void __munlock_vma_pages_range(struct vm_area_struct *vma,
+			      unsigned long start, unsigned long end)
+{
+}
+#endif /* CONFIG_UNEVICTABLE_LRU */
+
+/*
+ * mlock all pages in this vma range.  For mmap()/mremap()/...
+ */
+int mlock_vma_pages_range(struct vm_area_struct *vma,
+			unsigned long start, unsigned long end)
+{
+	int nr_pages = (end - start) / PAGE_SIZE;
+	BUG_ON(!(vma->vm_flags & VM_LOCKED));
+
+	/*
+	 * filter unlockable vmas
+	 */
+	if (vma->vm_flags & (VM_IO | VM_PFNMAP))
+		goto no_mlock;
+
+	if (!((vma->vm_flags & (VM_DONTEXPAND | VM_RESERVED)) ||
+			is_vm_hugetlb_page(vma) ||
+			vma == get_gate_vma(current)))
+		return __mlock_vma_pages_range(vma, start, end);
+
+	/*
+	 * User mapped kernel pages or huge pages:
+	 * make these pages present to populate the ptes, but
+	 * fall thru' to reset VM_LOCKED--no need to unlock, and
+	 * return nr_pages so these don't get counted against task's
+	 * locked limit.  huge pages are already counted against
+	 * locked vm limit.
+	 */
+	make_pages_present(start, end);
+
+no_mlock:
+	vma->vm_flags &= ~VM_LOCKED;	/* and don't come back! */
+	return nr_pages;		/* pages NOT mlocked */
+}
+
+
+/*
+ * munlock all pages in vma.   For munmap() and exit().
+ */
+void munlock_vma_pages_all(struct vm_area_struct *vma)
+{
+	vma->vm_flags &= ~VM_LOCKED;
+	__munlock_vma_pages_range(vma, vma->vm_start, vma->vm_end);
+}
+
+/*
+ * mlock_fixup  - handle mlock[all]/munlock[all] requests.
+ *
+ * Filters out "special" vmas -- VM_LOCKED never gets set for these, and
+ * munlock is a no-op.  However, for some special vmas, we go ahead and
+ * populate the ptes via make_pages_present().
+ *
+ * For vmas that pass the filters, merge/split as appropriate.
+ */
 static int mlock_fixup(struct vm_area_struct *vma, struct vm_area_struct **prev,
 	unsigned long start, unsigned long end, unsigned int newflags)
 {
-	struct mm_struct * mm = vma->vm_mm;
+	struct mm_struct *mm = vma->vm_mm;
 	pgoff_t pgoff;
-	int pages;
+	int nr_pages;
 	int ret = 0;
+	int lock = newflags & VM_LOCKED;
 
-	if (newflags == vma->vm_flags) {
-		*prev = vma;
-		goto out;
+	if (newflags == vma->vm_flags ||
+			(vma->vm_flags & (VM_IO | VM_PFNMAP)))
+		goto out;	/* don't set VM_LOCKED,  don't count */
+
+	if ((vma->vm_flags & (VM_DONTEXPAND | VM_RESERVED)) ||
+			is_vm_hugetlb_page(vma) ||
+			vma == get_gate_vma(current)) {
+		if (lock)
+			make_pages_present(start, end);
+		goto out;	/* don't set VM_LOCKED,  don't count */
 	}
 
 	pgoff = vma->vm_pgoff + ((start - vma->vm_start) >> PAGE_SHIFT);
···
 		vma = *prev;
 		goto success;
 	}
-
-	*prev = vma;
 
 	if (start != vma->vm_start) {
 		ret = split_vma(mm, vma, start, 1);
···
 
 success:
 	/*
+	 * Keep track of amount of locked VM.
+	 */
+	nr_pages = (end - start) >> PAGE_SHIFT;
+	if (!lock)
+		nr_pages = -nr_pages;
+	mm->locked_vm += nr_pages;
+
+	/*
 	 * vm_flags is protected by the mmap_sem held in write mode.
 	 * It's okay if try_to_unmap_one unmaps a page just after we
-	 * set VM_LOCKED, make_pages_present below will bring it back.
+	 * set VM_LOCKED, __mlock_vma_pages_range will bring it back.
 	 */
 	vma->vm_flags = newflags;
 
-	/*
-	 * Keep track of amount of locked VM.
-	 */
-	pages = (end - start) >> PAGE_SHIFT;
-	if (newflags & VM_LOCKED) {
-		pages = -pages;
-		if (!(newflags & VM_IO))
-			ret = make_pages_present(start, end);
-	}
+	if (lock) {
+		ret = __mlock_vma_pages_range(vma, start, end);
+		if (ret > 0) {
+			mm->locked_vm -= ret;
+			ret = 0;
+		}
+	} else
+		__munlock_vma_pages_range(vma, start, end);
 
-	mm->locked_vm -= pages;
 out:
+	*prev = vma;
 	return ret;
 }
 

mm/mmap.c

···
  * If the vma has a ->close operation then the driver probably needs to release
  * per-vma resources, so we don't attempt to merge those.
  */
-#define VM_SPECIAL (VM_IO | VM_DONTEXPAND | VM_RESERVED | VM_PFNMAP)
-
 static inline int is_mergeable_vma(struct vm_area_struct *vma,
 			struct file *file, unsigned long vm_flags)
 {

mm/nommu.c

···
 #include <asm/tlb.h>
 #include <asm/tlbflush.h>
 
+#include "internal.h"
+
 void *high_memory;
 struct page *mem_map;
 unsigned long max_mapnr;
···
 	return PAGE_SIZE << compound_order(page);
 }
 
-/*
- * get a list of pages in an address range belonging to the specified process
- * and indicate the VMA that covers each page
- * - this is potentially dodgy as we may end incrementing the page count of a
- *   slab page or a secondary page from a compound page
- * - don't permit access to VMAs that don't support it, such as I/O mappings
- */
-int get_user_pages(struct task_struct *tsk, struct mm_struct *mm,
-	unsigned long start, int len, int write, int force,
-	struct page **pages, struct vm_area_struct **vmas)
+int __get_user_pages(struct task_struct *tsk, struct mm_struct *mm,
+		     unsigned long start, int len, int flags,
+		struct page **pages, struct vm_area_struct **vmas)
 {
 	struct vm_area_struct *vma;
 	unsigned long vm_flags;
 	int i;
+	int write = !!(flags & GUP_FLAGS_WRITE);
+	int force = !!(flags & GUP_FLAGS_FORCE);
+	int ignore = !!(flags & GUP_FLAGS_IGNORE_VMA_PERMISSIONS);
 
 	/* calculate required read or write permissions.
 	 * - if 'force' is set, we only require the "MAY" flags.
···
 
 		/* protect what we can, including chardevs */
 		if (vma->vm_flags & (VM_IO | VM_PFNMAP) ||
-		    !(vm_flags & vma->vm_flags))
+		    (!ignore && !(vm_flags & vma->vm_flags)))
 			goto finish_or_fault;
 
 		if (pages) {
···
 
 finish_or_fault:
 	return i ? : -EFAULT;
+}
+
+
+/*
+ * get a list of pages in an address range belonging to the specified process
+ * and indicate the VMA that covers each page
+ * - this is potentially dodgy as we may end incrementing the page count of a
+ *   slab page or a secondary page from a compound page
+ * - don't permit access to VMAs that don't support it, such as I/O mappings
+ */
+int get_user_pages(struct task_struct *tsk, struct mm_struct *mm,
+	unsigned long start, int len, int write, int force,
+	struct page **pages, struct vm_area_struct **vmas)
+{
+	int flags = 0;
+
+	if (write)
+		flags |= GUP_FLAGS_WRITE;
+	if (force)
+		flags |= GUP_FLAGS_FORCE;
+
+	return __get_user_pages(tsk, mm,
+				start, len, flags,
+				pages, vmas);
 }
 EXPORT_SYMBOL(get_user_pages);
 

mm/page_alloc.c

···
 
 	page->flags &= ~(1 << PG_uptodate | 1 << PG_error | 1 << PG_reclaim |
 			1 << PG_referenced | 1 << PG_arch_1 |
-			1 << PG_owner_priv_1 | 1 << PG_mappedtodisk);
+			1 << PG_owner_priv_1 | 1 << PG_mappedtodisk
+#ifdef CONFIG_UNEVICTABLE_LRU
+			| 1 << PG_mlocked
+#endif
+			);
 	set_page_private(page, 0);
 	set_page_refcounted(page);
 

mm/rmap.c

···
 
 #include <asm/tlbflush.h>
 
+#include "internal.h"
+
 struct kmem_cache *anon_vma_cachep;
 
 /**
···
 	return NULL;
 }
 
+/**
+ * page_mapped_in_vma - check whether a page is really mapped in a VMA
+ * @page: the page to test
+ * @vma: the VMA to test
+ *
+ * Returns 1 if the page is mapped into the page tables of the VMA, 0
+ * if the page is not mapped into the page tables of this VMA.  Only
+ * valid for normal file or anonymous VMAs.
+ */
+static int page_mapped_in_vma(struct page *page, struct vm_area_struct *vma)
+{
+	unsigned long address;
+	pte_t *pte;
+	spinlock_t *ptl;
+
+	address = vma_address(page, vma);
+	if (address == -EFAULT)		/* out of vma range */
+		return 0;
+	pte = page_check_address(page, vma->vm_mm, address, &ptl, 1);
+	if (!pte)			/* the page is not in this mm */
+		return 0;
+	pte_unmap_unlock(pte, ptl);
+
+	return 1;
+}
+
 /*
  * Subfunctions of page_referenced: page_referenced_one called
  * repeatedly from either page_referenced_anon or page_referenced_file.
···
 	if (!pte)
 		goto out;
 
+	/*
+	 * Don't want to elevate referenced for mlocked page that gets this far,
+	 * in order that it progresses to try_to_unmap and is moved to the
+	 * unevictable list.
+	 */
 	if (vma->vm_flags & VM_LOCKED) {
-		referenced++;
 		*mapcount = 1;	/* break early from loop */
-	} else if (ptep_clear_flush_young_notify(vma, address, pte))
+		goto out_unmap;
+	}
+
+	if (ptep_clear_flush_young_notify(vma, address, pte))
 		referenced++;
 
 	/* Pretend the page is referenced if the task has the
···
 			rwsem_is_locked(&mm->mmap_sem))
 		referenced++;
 
+out_unmap:
 	(*mapcount)--;
 	pte_unmap_unlock(pte, ptl);
 out:
···
 		 */
 		if (mem_cont && !mm_match_cgroup(vma->vm_mm, mem_cont))
 			continue;
-		if ((vma->vm_flags & (VM_LOCKED|VM_MAYSHARE))
-				  == (VM_LOCKED|VM_MAYSHARE)) {
-			referenced++;
-			break;
-		}
 		referenced += page_referenced_one(page, vma, &mapcount);
 		if (!mapcount)
 			break;
···
 	 * If it's recently referenced (perhaps page_referenced
 	 * skipped over this mm) then we should reactivate it.
 	 */
-	if (!migration && ((vma->vm_flags & VM_LOCKED) ||
-			(ptep_clear_flush_young_notify(vma, address, pte)))) {
-		ret = SWAP_FAIL;
-		goto out_unmap;
-	}
+	if (!migration) {
+		if (vma->vm_flags & VM_LOCKED) {
+			ret = SWAP_MLOCK;
+			goto out_unmap;
+		}
+		if (ptep_clear_flush_young_notify(vma, address, pte)) {
+			ret = SWAP_FAIL;
+			goto out_unmap;
+		}
+  	}
 
 	/* Nuke the page table entry. */
 	flush_cache_page(vma, address, page_to_pfn(page));
···
  * For very sparsely populated VMAs this is a little inefficient - chances are
  * there there won't be many ptes located within the scan cluster.  In this case
  * maybe we could scan further - to the end of the pte page, perhaps.
+ *
+ * Mlocked pages:  check VM_LOCKED under mmap_sem held for read, if we can
+ * acquire it without blocking.  If vma locked, mlock the pages in the cluster,
+ * rather than unmapping them.  If we encounter the "check_page" that vmscan is
+ * trying to unmap, return SWAP_MLOCK, else default SWAP_AGAIN.
  */
 #define CLUSTER_SIZE	min(32*PAGE_SIZE, PMD_SIZE)
 #define CLUSTER_MASK	(~(CLUSTER_SIZE - 1))
 
-static void try_to_unmap_cluster(unsigned long cursor,
-	unsigned int *mapcount, struct vm_area_struct *vma)
+static int try_to_unmap_cluster(unsigned long cursor, unsigned int *mapcount,
+		struct vm_area_struct *vma, struct page *check_page)
 {
 	struct mm_struct *mm = vma->vm_mm;
 	pgd_t *pgd;
···
 	struct page *page;
 	unsigned long address;
 	unsigned long end;
+	int ret = SWAP_AGAIN;
+	int locked_vma = 0;
 
 	address = (vma->vm_start + cursor) & CLUSTER_MASK;
 	end = address + CLUSTER_SIZE;
···
 
 	pgd = pgd_offset(mm, address);
 	if (!pgd_present(*pgd))
-		return;
+		return ret;
 
 	pud = pud_offset(pgd, address);
 	if (!pud_present(*pud))
-		return;
+		return ret;
 
 	pmd = pmd_offset(pud, address);
 	if (!pmd_present(*pmd))
-		return;
+		return ret;
+
+	/*
+	 * MLOCK_PAGES => feature is configured.
+	 * if we can acquire the mmap_sem for read, and vma is VM_LOCKED,
+	 * keep the sem while scanning the cluster for mlocking pages.
+	 */
+	if (MLOCK_PAGES && down_read_trylock(&vma->vm_mm->mmap_sem)) {
+		locked_vma = (vma->vm_flags & VM_LOCKED);
+		if (!locked_vma)
+			up_read(&vma->vm_mm->mmap_sem); /* don't need it */
+	}
 
 	pte = pte_offset_map_lock(mm, pmd, address, &ptl);
 
···
 			continue;
 		page = vm_normal_page(vma, address, *pte);
 		BUG_ON(!page || PageAnon(page));
+
+		if (locked_vma) {
+			mlock_vma_page(page);   /* no-op if already mlocked */
+			if (page == check_page)
+				ret = SWAP_MLOCK;
+			continue;	/* don't unmap */
+		}
 
 		if (ptep_clear_flush_young_notify(vma, address, pte))
 			continue;
···
 		(*mapcount)--;
 	}
 	pte_unmap_unlock(pte - 1, ptl);
+	if (locked_vma)
+		up_read(&vma->vm_mm->mmap_sem);
+	return ret;
 }
 
-static int try_to_unmap_anon(struct page *page, int migration)
+/*
+ * common handling for pages mapped in VM_LOCKED vmas
+ */
+static int try_to_mlock_page(struct page *page, struct vm_area_struct *vma)
+{
+	int mlocked = 0;
+
+	if (down_read_trylock(&vma->vm_mm->mmap_sem)) {
+		if (vma->vm_flags & VM_LOCKED) {
+			mlock_vma_page(page);
+			mlocked++;	/* really mlocked the page */
+		}
+		up_read(&vma->vm_mm->mmap_sem);
+	}
+	return mlocked;
+}
+
+/**
+ * try_to_unmap_anon - unmap or unlock anonymous page using the object-based
+ * rmap method
+ * @page: the page to unmap/unlock
+ * @unlock:  request for unlock rather than unmap [unlikely]
+ * @migration:  unmapping for migration - ignored if @unlock
+ *
+ * Find all the mappings of a page using the mapping pointer and the vma chains
+ * contained in the anon_vma struct it points to.
+ *
+ * This function is only called from try_to_unmap/try_to_munlock for
+ * anonymous pages.
+ * When called from try_to_munlock(), the mmap_sem of the mm containing the vma
+ * where the page was found will be held for write.  So, we won't recheck
+ * vm_flags for that VMA.  That should be OK, because that vma shouldn't be
+ * 'LOCKED.
+ */
+static int try_to_unmap_anon(struct page *page, int unlock, int migration)
 {
 	struct anon_vma *anon_vma;
 	struct vm_area_struct *vma;
+	unsigned int mlocked = 0;
 	int ret = SWAP_AGAIN;
+
+	if (MLOCK_PAGES && unlikely(unlock))
+		ret = SWAP_SUCCESS;	/* default for try_to_munlock() */
 
 	anon_vma = page_lock_anon_vma(page);
 	if (!anon_vma)
 		return ret;
 
 	list_for_each_entry(vma, &anon_vma->head, anon_vma_node) {
-		ret = try_to_unmap_one(page, vma, migration);
-		if (ret == SWAP_FAIL || !page_mapped(page))
-			break;
+		if (MLOCK_PAGES && unlikely(unlock)) {
+			if (!((vma->vm_flags & VM_LOCKED) &&
+			      page_mapped_in_vma(page, vma)))
+				continue;  /* must visit all unlocked vmas */
+			ret = SWAP_MLOCK;  /* saw at least one mlocked vma */
+		} else {
+			ret = try_to_unmap_one(page, vma, migration);
+			if (ret == SWAP_FAIL || !page_mapped(page))
+				break;
+		}
+		if (ret == SWAP_MLOCK) {
+			mlocked = try_to_mlock_page(page, vma);
+			if (mlocked)
+				break;	/* stop if actually mlocked page */
+		}
 	}
 
 	page_unlock_anon_vma(anon_vma);
+
+	if (mlocked)
+		ret = SWAP_MLOCK;	/* actually mlocked the page */
+	else if (ret == SWAP_MLOCK)
+		ret = SWAP_AGAIN;	/* saw VM_LOCKED vma */
+
 	return ret;
 }
 
 /**
- * try_to_unmap_file - unmap file page using the object-based rmap method
- * @page: the page to unmap
- * @migration: migration flag
+ * try_to_unmap_file - unmap/unlock file page using the object-based rmap method
+ * @page: the page to unmap/unlock
+ * @unlock:  request for unlock rather than unmap [unlikely]
+ * @migration:  unmapping for migration - ignored if @unlock
  *
  * Find all the mappings of a page using the mapping pointer and the vma chains
  * contained in the address_space struct it points to.
  *
- * This function is only called from try_to_unmap for object-based pages.
+ * This function is only called from try_to_unmap/try_to_munlock for
+ * object-based pages.
+ * When called from try_to_munlock(), the mmap_sem of the mm containing the vma
+ * where the page was found will be held for write.  So, we won't recheck
+ * vm_flags for that VMA.  That should be OK, because that vma shouldn't be
+ * 'LOCKED.
  */
-static int try_to_unmap_file(struct page *page, int migration)
+static int try_to_unmap_file(struct page *page, int unlock, int migration)
 {
 	struct address_space *mapping = page->mapping;
 	pgoff_t pgoff = page->index << (PAGE_CACHE_SHIFT - PAGE_SHIFT);
···
 	unsigned long max_nl_cursor = 0;
 	unsigned long max_nl_size = 0;
 	unsigned int mapcount;
+	unsigned int mlocked = 0;
+
+	if (MLOCK_PAGES && unlikely(unlock))
+		ret = SWAP_SUCCESS;	/* default for try_to_munlock() */
 
 	spin_lock(&mapping->i_mmap_lock);
 	vma_prio_tree_foreach(vma, &iter, &mapping->i_mmap, pgoff, pgoff) {
-		ret = try_to_unmap_one(page, vma, migration);
-		if (ret == SWAP_FAIL || !page_mapped(page))
-			goto out;
+		if (MLOCK_PAGES && unlikely(unlock)) {
+			if (!(vma->vm_flags & VM_LOCKED))
+				continue;	/* must visit all vmas */
+			ret = SWAP_MLOCK;
+		} else {
+			ret = try_to_unmap_one(page, vma, migration);
+			if (ret == SWAP_FAIL || !page_mapped(page))
+				goto out;
+		}
+		if (ret == SWAP_MLOCK) {
+			mlocked = try_to_mlock_page(page, vma);
+			if (mlocked)
+				break;  /* stop if actually mlocked page */
+		}
 	}
+
+	if (mlocked)
+		goto out;
 
 	if (list_empty(&mapping->i_mmap_nonlinear))
 		goto out;
 
 	list_for_each_entry(vma, &mapping->i_mmap_nonlinear,
 						shared.vm_set.list) {
-		if ((vma->vm_flags & VM_LOCKED) && !migration)
+		if (MLOCK_PAGES && unlikely(unlock)) {
+			if (!(vma->vm_flags & VM_LOCKED))
+				continue;	/* must visit all vmas */
+			ret = SWAP_MLOCK;	/* leave mlocked == 0 */
+			goto out;		/* no need to look further */
+		}
+		if (!MLOCK_PAGES && !migration && (vma->vm_flags & VM_LOCKED))
 			continue;
 		cursor = (unsigned long) vma->vm_private_data;
 		if (cursor > max_nl_cursor)
···
 			max_nl_size = cursor;
 	}
 
-	if (max_nl_size == 0) {	/* any nonlinears locked or reserved */
+	if (max_nl_size == 0) {	/* all nonlinears locked or reserved ? */
 		ret = SWAP_FAIL;
 		goto out;
 	}
···
 	do {
 		list_for_each_entry(vma, &mapping->i_mmap_nonlinear,
 						shared.vm_set.list) {
-			if ((vma->vm_flags & VM_LOCKED) && !migration)
+			if (!MLOCK_PAGES && !migration &&
+			    (vma->vm_flags & VM_LOCKED))
 				continue;
 			cursor = (unsigned long) vma->vm_private_data;
 			while ( cursor < max_nl_cursor &&
 				cursor < vma->vm_end - vma->vm_start) {
-				try_to_unmap_cluster(cursor, &mapcount, vma);
+				ret = try_to_unmap_cluster(cursor, &mapcount,
+								vma, page);
+				if (ret == SWAP_MLOCK)
+					mlocked = 2;	/* to return below */
 				cursor += CLUSTER_SIZE;
 				vma->vm_private_data = (void *) cursor;
 				if ((int)mapcount <= 0)
···
 		vma->vm_private_data = NULL;
 out:
 	spin_unlock(&mapping->i_mmap_lock);
+	if (mlocked)
+		ret = SWAP_MLOCK;	/* actually mlocked the page */
+	else if (ret == SWAP_MLOCK)
+		ret = SWAP_AGAIN;	/* saw VM_LOCKED vma */
 	return ret;
 }
 
···
  * SWAP_SUCCESS	- we succeeded in removing all mappings
  * SWAP_AGAIN	- we missed a mapping, try again later
  * SWAP_FAIL	- the page is unswappable
+ * SWAP_MLOCK	- page is mlocked.
  */
 int try_to_unmap(struct page *page, int migration)
 {
···
 	BUG_ON(!PageLocked(page));
 
 	if (PageAnon(page))
-		ret = try_to_unmap_anon(page, migration);
+		ret = try_to_unmap_anon(page, 0, migration);
 	else
-		ret = try_to_unmap_file(page, migration);
-
-	if (!page_mapped(page))
+		ret = try_to_unmap_file(page, 0, migration);
+	if (ret != SWAP_MLOCK && !page_mapped(page))
 		ret = SWAP_SUCCESS;
 	return ret;
 }
 
+#ifdef CONFIG_UNEVICTABLE_LRU
+/**
+ * try_to_munlock - try to munlock a page
+ * @page: the page to be munlocked
+ *
+ * Called from munlock code.  Checks all of the VMAs mapping the page
+ * to make sure nobody else has this page mlocked. The page will be
+ * returned with PG_mlocked cleared if no other vmas have it mlocked.
+ *
+ * Return values are:
+ *
+ * SWAP_SUCCESS	- no vma's holding page mlocked.
+ * SWAP_AGAIN	- page mapped in mlocked vma -- couldn't acquire mmap sem
+ * SWAP_MLOCK	- page is now mlocked.
+ */
+int try_to_munlock(struct page *page)
+{
+	VM_BUG_ON(!PageLocked(page) || PageLRU(page));
+
+	if (PageAnon(page))
+		return try_to_unmap_anon(page, 1, 0);
+	else
+		return try_to_unmap_file(page, 1, 0);
+}
+#endif

mm/swap.c

···
 	put_cpu();
 }
 
-#ifdef CONFIG_NUMA
+#if defined(CONFIG_NUMA) || defined(CONFIG_UNEVICTABLE_LRU)
 static void lru_add_drain_per_cpu(struct work_struct *dummy)
 {
 	lru_add_drain();

mm/vmscan.c

···
 
 		sc->nr_scanned++;
 
-		if (unlikely(!page_evictable(page, NULL))) {
-			unlock_page(page);
-			putback_lru_page(page);
-			continue;
-		}
+		if (unlikely(!page_evictable(page, NULL)))
+			goto cull_mlocked;
 
 		if (!sc->may_swap && page_mapped(page))
 			goto keep_locked;
···
 		 * Anonymous process memory has backing store?
 		 * Try to allocate it some swap space here.
 		 */
-		if (PageAnon(page) && !PageSwapCache(page))
+		if (PageAnon(page) && !PageSwapCache(page)) {
+			switch (try_to_munlock(page)) {
+			case SWAP_FAIL:		/* shouldn't happen */
+			case SWAP_AGAIN:
+				goto keep_locked;
+			case SWAP_MLOCK:
+				goto cull_mlocked;
+			case SWAP_SUCCESS:
+				; /* fall thru'; add to swap cache */
+			}
 			if (!add_to_swap(page, GFP_ATOMIC))
 				goto activate_locked;
+		}
 #endif /* CONFIG_SWAP */
 
 		mapping = page_mapping(page);
···
 				goto activate_locked;
 			case SWAP_AGAIN:
 				goto keep_locked;
+			case SWAP_MLOCK:
+				goto cull_mlocked;
 			case SWAP_SUCCESS:
 				; /* try to free the page below */
 			}
···
 		}
 		continue;
 
+cull_mlocked:
+		unlock_page(page);
+		putback_lru_page(page);
+		continue;
+
 activate_locked:
 		/* Not a candidate for swapping, so reclaim swap space. */
 		if (PageSwapCache(page) && vm_swap_full())
···
 		unlock_page(page);
 keep:
 		list_add(&page->lru, &ret_pages);
-		VM_BUG_ON(PageLRU(page));
+		VM_BUG_ON(PageLRU(page) || PageUnevictable(page));
 	}
 	list_splice(&ret_pages, page_list);
 	if (pagevec_count(&freed_pvec))
···
  * @vma: the VMA in which the page is or will be mapped, may be NULL
  *
  * Test whether page is evictable--i.e., should be placed on active/inactive
- * lists vs unevictable list.
+ * lists vs unevictable list.  The vma argument is !NULL when called from the
+ * fault path to determine how to instantate a new page.
  *
  * Reasons page might not be evictable:
  * (1) page's mapping marked unevictable
+ * (2) page is part of an mlocked VMA
  *
- * TODO - later patches
  */
 int page_evictable(struct page *page, struct vm_area_struct *vma)
 {
···
 	if (mapping_unevictable(page_mapping(page)))
 		return 0;
 
-	/* TODO:  test page [!]evictable conditions */
+	if (PageMlocked(page) || (vma && is_mlocked_vma(vma, page)))
+		return 0;
 
 	return 1;
 }