[Devel] [PATCH rh7 9/9] mm: introduce idle page tracking

[Vladimir Davydov]

From: Vladimir Davydov <vdavydov at parallels.com>

Knowing the portion of memory that is not used by a certain application or
memory cgroup (idle memory) can be useful for partitioning the system
efficiently, e.g.  by setting memory cgroup limits appropriately.
Currently, the only means to estimate the amount of idle memory provided
by the kernel is /proc/PID/{clear_refs,smaps}: the user can clear the
access bit for all pages mapped to a particular process by writing 1 to
clear_refs, wait for some time, and then count smaps:Referenced.  However,
this method has two serious shortcomings:

 - it does not count unmapped file pages
 - it affects the reclaimer logic

To overcome these drawbacks, this patch introduces two new page flags,
Idle and Young, and a new sysfs file, /sys/kernel/mm/page_idle/bitmap.
A page's Idle flag can only be set from userspace by setting bit in
/sys/kernel/mm/page_idle/bitmap at the offset corresponding to the page,
and it is cleared whenever the page is accessed either through page tables
(it is cleared in page_referenced() in this case) or using the read(2)
system call (mark_page_accessed()). Thus by setting the Idle flag for
pages of a particular workload, which can be found e.g.  by reading
/proc/PID/pagemap, waiting for some time to let the workload access its
working set, and then reading the bitmap file, one can estimate the amount
of pages that are not used by the workload.

The Young page flag is used to avoid interference with the memory
reclaimer.  A page's Young flag is set whenever the Access bit of a page
table entry pointing to the page is cleared by writing to the bitmap file.
If page_referenced() is called on a Young page, it will add 1 to its
return value, therefore concealing the fact that the Access bit was
cleared.

Note, since there is no room for extra page flags on 32 bit, this feature
uses extended page flags when compiled on 32 bit.

[akpm at linux-foundation.org: fix build]
[akpm at linux-foundation.org: kpageidle requires an MMU]
[akpm at linux-foundation.org: decouple from page-flags rework]
Signed-off-by: Vladimir Davydov <vdavydov at parallels.com>
Reviewed-by: Andres Lagar-Cavilla <andreslc at google.com>
Cc: Minchan Kim <minchan at kernel.org>
Cc: Raghavendra K T <raghavendra.kt at linux.vnet.ibm.com>
Cc: Johannes Weiner <hannes at cmpxchg.org>
Cc: Michal Hocko <mhocko at suse.cz>
Cc: Greg Thelen <gthelen at google.com>
Cc: Michel Lespinasse <walken at google.com>
Cc: David Rientjes <rientjes at google.com>
Cc: Pavel Emelyanov <xemul at parallels.com>
Cc: Cyrill Gorcunov <gorcunov at openvz.org>
Cc: Jonathan Corbet <corbet at lwn.net>
Signed-off-by: Andrew Morton <akpm at linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds at linux-foundation.org>

(cherry picked from commit 33c3fc71c8cfa3cc3a98beaa901c069c177dc295)
Signed-off-by: Vladimir Davydov <vdavydov at virtuozzo.com>

Conflicts:
	fs/proc/task_mmu.c
	include/linux/mmu_notifier.h
	include/linux/page-flags.h
	include/linux/page_idle.h
	include/linux/page_ext.h
	mm/Kconfig
	mm/Makefile
	mm/debug.c
	mm/huge_memory.c
	mm/page_alloc.c
	mm/page_ext.c
	mm/page_idle.c
	mm/rmap.c
	mm/swap.c
---
 Documentation/vm/00-INDEX               |   2 +
 Documentation/vm/idle_page_tracking.txt |  98 +++++++++++++++
 fs/proc/task_mmu.c                      |   4 +-
 include/linux/page-flags.h              |  11 ++
 include/linux/page_idle.h               |  69 +++++++++++
 mm/Kconfig                              |  12 ++
 mm/Makefile                             |   1 +
 mm/huge_memory.c                        |  12 +-
 mm/migrate.c                            |   6 +
 mm/page_alloc.c                         |   4 +
 mm/page_idle.c                          | 209 ++++++++++++++++++++++++++++++++
 mm/rmap.c                               |   6 +
 mm/swap.c                               |   3 +
 13 files changed, 434 insertions(+), 3 deletions(-)
 create mode 100644 Documentation/vm/idle_page_tracking.txt
 create mode 100644 include/linux/page_idle.h
 create mode 100644 mm/page_idle.c

diff --git a/Documentation/vm/00-INDEX b/Documentation/vm/00-INDEX
index 5481c8ba3412..e15ed3bafd76 100644
--- a/Documentation/vm/00-INDEX
+++ b/Documentation/vm/00-INDEX
@@ -12,6 +12,8 @@ hugetlbpage.txt
 	- a brief summary of hugetlbpage support in the Linux kernel.
 hwpoison.txt
 	- explains what hwpoison is
+idle_page_tracking.txt
+	- description of the idle page tracking feature.
 ksm.txt
 	- how to use the Kernel Samepage Merging feature.
 locking
diff --git a/Documentation/vm/idle_page_tracking.txt b/Documentation/vm/idle_page_tracking.txt
new file mode 100644
index 000000000000..85dcc3bb85dc
--- /dev/null
+++ b/Documentation/vm/idle_page_tracking.txt
@@ -0,0 +1,98 @@
+MOTIVATION
+
+The idle page tracking feature allows to track which memory pages are being
+accessed by a workload and which are idle. This information can be useful for
+estimating the workload's working set size, which, in turn, can be taken into
+account when configuring the workload parameters, setting memory cgroup limits,
+or deciding where to place the workload within a compute cluster.
+
+It is enabled by CONFIG_IDLE_PAGE_TRACKING=y.
+
+USER API
+
+The idle page tracking API is located at /sys/kernel/mm/page_idle. Currently,
+it consists of the only read-write file, /sys/kernel/mm/page_idle/bitmap.
+
+The file implements a bitmap where each bit corresponds to a memory page. The
+bitmap is represented by an array of 8-byte integers, and the page at PFN #i is
+mapped to bit #i%64 of array element #i/64, byte order is native. When a bit is
+set, the corresponding page is idle.
+
+A page is considered idle if it has not been accessed since it was marked idle
+(for more details on what "accessed" actually means see the IMPLEMENTATION
+DETAILS section). To mark a page idle one has to set the bit corresponding to
+the page by writing to the file. A value written to the file is OR-ed with the
+current bitmap value.
+
+Only accesses to user memory pages are tracked. These are pages mapped to a
+process address space, page cache and buffer pages, swap cache pages. For other
+page types (e.g. SLAB pages) an attempt to mark a page idle is silently ignored,
+and hence such pages are never reported idle.
+
+For huge pages the idle flag is set only on the head page, so one has to read
+/proc/kpageflags in order to correctly count idle huge pages.
+
+Reading from or writing to /sys/kernel/mm/page_idle/bitmap will return
+-EINVAL if you are not starting the read/write on an 8-byte boundary, or
+if the size of the read/write is not a multiple of 8 bytes. Writing to
+this file beyond max PFN will return -ENXIO.
+
+That said, in order to estimate the amount of pages that are not used by a
+workload one should:
+
+ 1. Mark all the workload's pages as idle by setting corresponding bits in
+    /sys/kernel/mm/page_idle/bitmap. The pages can be found by reading
+    /proc/pid/pagemap if the workload is represented by a process, or by
+    filtering out alien pages using /proc/kpagecgroup in case the workload is
+    placed in a memory cgroup.
+
+ 2. Wait until the workload accesses its working set.
+
+ 3. Read /sys/kernel/mm/page_idle/bitmap and count the number of bits set. If
+    one wants to ignore certain types of pages, e.g. mlocked pages since they
+    are not reclaimable, he or she can filter them out using /proc/kpageflags.
+
+See Documentation/vm/pagemap.txt for more information about /proc/pid/pagemap,
+/proc/kpageflags, and /proc/kpagecgroup.
+
+IMPLEMENTATION DETAILS
+
+The kernel internally keeps track of accesses to user memory pages in order to
+reclaim unreferenced pages first on memory shortage conditions. A page is
+considered referenced if it has been recently accessed via a process address
+space, in which case one or more PTEs it is mapped to will have the Accessed bit
+set, or marked accessed explicitly by the kernel (see mark_page_accessed()). The
+latter happens when:
+
+ - a userspace process reads or writes a page using a system call (e.g. read(2)
+   or write(2))
+
+ - a page that is used for storing filesystem buffers is read or written,
+   because a process needs filesystem metadata stored in it (e.g. lists a
+   directory tree)
+
+ - a page is accessed by a device driver using get_user_pages()
+
+When a dirty page is written to swap or disk as a result of memory reclaim or
+exceeding the dirty memory limit, it is not marked referenced.
+
+The idle memory tracking feature adds a new page flag, the Idle flag. This flag
+is set manually, by writing to /sys/kernel/mm/page_idle/bitmap (see the USER API
+section), and cleared automatically whenever a page is referenced as defined
+above.
+
+When a page is marked idle, the Accessed bit must be cleared in all PTEs it is
+mapped to, otherwise we will not be able to detect accesses to the page coming
+from a process address space. To avoid interference with the reclaimer, which,
+as noted above, uses the Accessed bit to promote actively referenced pages, one
+more page flag is introduced, the Young flag. When the PTE Accessed bit is
+cleared as a result of setting or updating a page's Idle flag, the Young flag
+is set on the page. The reclaimer treats the Young flag as an extra PTE
+Accessed bit and therefore will consider such a page as referenced.
+
+Since the idle memory tracking feature is based on the memory reclaimer logic,
+it only works with pages that are on an LRU list, other pages are silently
+ignored. That means it will ignore a user memory page if it is isolated, but
+since there are usually not many of them, it should not affect the overall
+result noticeably. In order not to stall scanning of the idle page bitmap,
+locked pages may be skipped too.
diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
index d0e311f526df..f8d1cae1c1b3 100644
--- a/fs/proc/task_mmu.c
+++ b/fs/proc/task_mmu.c
@@ -12,6 +12,7 @@
 #include <linux/swap.h>
 #include <linux/swapops.h>
 #include <linux/mmu_notifier.h>
+#include <linux/page_idle.h>
 
 #include <asm/elf.h>
 #include <asm/uaccess.h>
@@ -480,7 +481,7 @@ static void smaps_pte_entry(pte_t ptent, unsigned long addr,
 
 	mss->resident += ptent_size;
 	/* Accumulate the size in pages that have been accessed. */
-	if (pte_young(ptent) || PageReferenced(page))
+	if (pte_young(ptent) || page_is_young(page) || PageReferenced(page))
 		mss->referenced += ptent_size;
 	mapcount = page_mapcount(page);
 	if (mapcount >= 2) {
@@ -776,6 +777,7 @@ static int clear_refs_pte_range(pmd_t *pmd, unsigned long addr,
 
 		/* Clear accessed and referenced bits. */
 		ptep_test_and_clear_young(vma, addr, pte);
+		test_and_clear_page_young(page);
 		ClearPageReferenced(page);
 	}
 	pte_unmap_unlock(pte - 1, ptl);
diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h
index b529ed7ba3ac..28f5c4ac98fc 100644
--- a/include/linux/page-flags.h
+++ b/include/linux/page-flags.h
@@ -109,6 +109,10 @@ enum pageflags {
 #ifdef CONFIG_TRANSPARENT_HUGEPAGE
 	PG_compound_lock,
 #endif
+#ifdef CONFIG_IDLE_PAGE_TRACKING
+	PG_young,
+	PG_idle,
+#endif
 	__NR_PAGEFLAGS,
 
 	/* Filesystems */
@@ -275,6 +279,13 @@ PAGEFLAG_FALSE(HWPoison)
 #define __PG_HWPOISON 0
 #endif
 
+#ifdef CONFIG_IDLE_PAGE_TRACKING
+TESTPAGEFLAG(Young, young)
+SETPAGEFLAG(Young, young)
+TESTCLEARFLAG(Young, young)
+PAGEFLAG(Idle, idle)
+#endif
+
 u64 stable_page_flags(struct page *page);
 
 static inline int PageUptodate(struct page *page)
diff --git a/include/linux/page_idle.h b/include/linux/page_idle.h
new file mode 100644
index 000000000000..fc18a92873f2
--- /dev/null
+++ b/include/linux/page_idle.h
@@ -0,0 +1,69 @@
+#ifndef _LINUX_MM_PAGE_IDLE_H
+#define _LINUX_MM_PAGE_IDLE_H
+
+#include <linux/page-flags.h>
+
+#ifdef CONFIG_IDLE_PAGE_TRACKING
+
+static inline bool page_is_young(struct page *page)
+{
+	return PageYoung(page);
+}
+
+static inline void set_page_young(struct page *page)
+{
+	SetPageYoung(page);
+}
+
+static inline bool test_and_clear_page_young(struct page *page)
+{
+	return TestClearPageYoung(page);
+}
+
+static inline bool page_is_idle(struct page *page)
+{
+	return PageIdle(page);
+}
+
+static inline void set_page_idle(struct page *page)
+{
+	SetPageIdle(page);
+}
+
+static inline void clear_page_idle(struct page *page)
+{
+	ClearPageIdle(page);
+}
+
+#else /* !CONFIG_IDLE_PAGE_TRACKING */
+
+static inline bool page_is_young(struct page *page)
+{
+	return false;
+}
+
+static inline void set_page_young(struct page *page)
+{
+}
+
+static inline bool test_and_clear_page_young(struct page *page)
+{
+	return false;
+}
+
+static inline bool page_is_idle(struct page *page)
+{
+	return false;
+}
+
+static inline void set_page_idle(struct page *page)
+{
+}
+
+static inline void clear_page_idle(struct page *page)
+{
+}
+
+#endif /* CONFIG_IDLE_PAGE_TRACKING */
+
+#endif /* _LINUX_MM_PAGE_IDLE_H */
diff --git a/mm/Kconfig b/mm/Kconfig
index 41d8ec743787..e8fca85c1fb9 100644
--- a/mm/Kconfig
+++ b/mm/Kconfig
@@ -572,3 +572,15 @@ config TSWAP
 	  stores reclaimed pages in memory without any modifications. It is
 	  only worth enabling if used along with memory cgroups in order to
 	  cache pages which were reclaimed on local pressure.
+
+config IDLE_PAGE_TRACKING
+	bool "Enable idle page tracking"
+	depends on SYSFS && MMU && 64BIT
+	help
+	  This feature allows to estimate the amount of user pages that have
+	  not been touched during a given period of time. This information can
+	  be useful to tune memory cgroup limits and/or for job placement
+	  within a compute cluster.
+
+	  See Documentation/vm/idle_page_tracking.txt for more details.
+
diff --git a/mm/Makefile b/mm/Makefile
index dff9c21ea1f6..e499a0d03988 100644
--- a/mm/Makefile
+++ b/mm/Makefile
@@ -67,3 +67,4 @@ obj-$(CONFIG_MEMORY_ISOLATION) += page_isolation.o
 obj-$(CONFIG_ZBUD)	+= zbud.o
 obj-$(CONFIG_TCACHE) += tcache.o
 obj-$(CONFIG_TSWAP) += tswap.o
+obj-$(CONFIG_IDLE_PAGE_TRACKING) += page_idle.o
diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index f4d55870319d..6de41efe035b 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -21,6 +21,7 @@
 #include <linux/pagemap.h>
 #include <linux/migrate.h>
 #include <linux/hashtable.h>
+#include <linux/page_idle.h>
 
 #include <asm/tlb.h>
 #include <asm/pgalloc.h>
@@ -1743,6 +1744,11 @@ static void __split_huge_page_refcount(struct page *page,
 		/* clear PageTail before overwriting first_page */
 		smp_wmb();
 
+		if (page_is_young(page))
+			set_page_young(page_tail);
+		if (page_is_idle(page))
+			set_page_idle(page_tail);
+
 		/*
 		 * __split_huge_page_splitting() already set the
 		 * splitting bit in all pmd that could map this
@@ -2216,7 +2222,8 @@ static int __collapse_huge_page_isolate(struct vm_area_struct *vma,
 		VM_BUG_ON_PAGE(PageLRU(page), page);
 
 		/* If there is no mapped pte young don't collapse the page */
-		if (pte_young(pteval) || PageReferenced(page) ||
+		if (pte_young(pteval) ||
+		    page_is_young(page) || PageReferenced(page) ||
 		    mmu_notifier_test_young(vma->vm_mm, address))
 			referenced = 1;
 	}
@@ -2590,7 +2597,8 @@ static int khugepaged_scan_pmd(struct mm_struct *mm,
 		/* cannot use mapcount: can't collapse if there's a gup pin */
 		if (page_count(page) != 1)
 			goto out_unmap;
-		if (pte_young(pteval) || PageReferenced(page) ||
+		if (pte_young(pteval) ||
+		    page_is_young(page) || PageReferenced(page) ||
 		    mmu_notifier_test_young(vma->vm_mm, address))
 			referenced = 1;
 	}
diff --git a/mm/migrate.c b/mm/migrate.c
index 1002661f6ceb..c608326dbc3d 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -37,6 +37,7 @@
 #include <linux/gfp.h>
 #include <linux/balloon_compaction.h>
 #include <linux/mmu_notifier.h>
+#include <linux/page_idle.h>
 
 #include <asm/tlbflush.h>
 
@@ -530,6 +531,11 @@ void migrate_page_copy(struct page *newpage, struct page *page)
 			__set_page_dirty_nobuffers(newpage);
  	}
 
+	if (page_is_young(page))
+		set_page_young(newpage);
+	if (page_is_idle(page))
+		set_page_idle(newpage);
+
 	/*
 	 * Copy NUMA information to the new page, to prevent over-eager
 	 * future migrations of this same page.
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index f271a754a1e7..f70c5f4da2a2 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -6471,6 +6471,10 @@ static const struct trace_print_flags pageflag_names[] = {
 #ifdef CONFIG_TRANSPARENT_HUGEPAGE
 	{1UL << PG_compound_lock,	"compound_lock"	},
 #endif
+#ifdef CONFIG_IDLE_PAGE_TRACKING
+	{1UL << PG_young,		"young"		},
+	{1UL << PG_idle,		"idle"		},
+#endif
 };
 
 static void dump_page_flags(unsigned long flags)
diff --git a/mm/page_idle.c b/mm/page_idle.c
new file mode 100644
index 000000000000..c09a5a28264f
--- /dev/null
+++ b/mm/page_idle.c
@@ -0,0 +1,209 @@
+#include <linux/init.h>
+#include <linux/bootmem.h>
+#include <linux/fs.h>
+#include <linux/sysfs.h>
+#include <linux/kobject.h>
+#include <linux/mm.h>
+#include <linux/mmzone.h>
+#include <linux/pagemap.h>
+#include <linux/rmap.h>
+#include <linux/mmu_notifier.h>
+#include <linux/ksm.h>
+#include <linux/page_idle.h>
+
+#define BITMAP_CHUNK_SIZE	sizeof(u64)
+#define BITMAP_CHUNK_BITS	(BITMAP_CHUNK_SIZE * BITS_PER_BYTE)
+
+/*
+ * Idle page tracking only considers user memory pages, for other types of
+ * pages the idle flag is always unset and an attempt to set it is silently
+ * ignored.
+ *
+ * We treat a page as a user memory page if it is on an LRU list, because it is
+ * always safe to pass such a page to rmap_walk(), which is essential for idle
+ * page tracking. With such an indicator of user pages we can skip isolated
+ * pages, but since there are not usually many of them, it will hardly affect
+ * the overall result.
+ *
+ * This function tries to get a user memory page by pfn as described above.
+ */
+static struct page *page_idle_get_page(unsigned long pfn)
+{
+	struct page *page;
+	struct zone *zone;
+
+	if (!pfn_valid(pfn))
+		return NULL;
+
+	page = pfn_to_page(pfn);
+	if (!page || !PageLRU(page) ||
+	    !get_page_unless_zero(page))
+		return NULL;
+
+	zone = page_zone(page);
+	spin_lock_irq(&zone->lru_lock);
+	if (unlikely(!PageLRU(page))) {
+		put_page(page);
+		page = NULL;
+	}
+	spin_unlock_irq(&zone->lru_lock);
+	return page;
+}
+
+static int page_idle_clear_pte_refs_one(struct page *page,
+					struct vm_area_struct *vma,
+					unsigned long addr, void *arg)
+{
+	struct mm_struct *mm = vma->vm_mm;
+	spinlock_t *ptl;
+	pmd_t *pmd;
+	pte_t *pte;
+	bool referenced = false;
+
+	if (unlikely(PageTransHuge(page))) {
+		pmd = page_check_address_pmd(page, mm, addr,
+					     PAGE_CHECK_ADDRESS_PMD_FLAG, &ptl);
+		if (pmd) {
+			referenced = pmdp_clear_young_notify(vma, addr, pmd);
+			spin_unlock(ptl);
+		}
+	} else {
+		pte = page_check_address(page, mm, addr, &ptl, 0);
+		if (pte) {
+			referenced = ptep_clear_young_notify(vma, addr, pte);
+			pte_unmap_unlock(pte, ptl);
+		}
+	}
+	if (referenced) {
+		clear_page_idle(page);
+		/*
+		 * We cleared the referenced bit in a mapping to this page. To
+		 * avoid interference with page reclaim, mark it young so that
+		 * page_referenced() will return > 0.
+		 */
+		set_page_young(page);
+	}
+	return SWAP_AGAIN;
+}
+
+static void page_idle_clear_pte_refs(struct page *page)
+{
+	if (!page_mapped(page) ||
+	    !page_rmapping(page))
+		return;
+
+	if (!trylock_page(page))
+		return;
+
+	rmap_walk(page, page_idle_clear_pte_refs_one, NULL);
+	unlock_page(page);
+}
+
+static ssize_t page_idle_bitmap_read(struct file *file, struct kobject *kobj,
+				     struct bin_attribute *attr, char *buf,
+				     loff_t pos, size_t count)
+{
+	u64 *out = (u64 *)buf;
+	struct page *page;
+	unsigned long pfn, end_pfn;
+	int bit;
+
+	if (pos % BITMAP_CHUNK_SIZE || count % BITMAP_CHUNK_SIZE)
+		return -EINVAL;
+
+	pfn = pos * BITS_PER_BYTE;
+	if (pfn >= max_pfn)
+		return 0;
+
+	end_pfn = pfn + count * BITS_PER_BYTE;
+	if (end_pfn > max_pfn)
+		end_pfn = ALIGN(max_pfn, BITMAP_CHUNK_BITS);
+
+	for (; pfn < end_pfn; pfn++) {
+		bit = pfn % BITMAP_CHUNK_BITS;
+		if (!bit)
+			*out = 0ULL;
+		page = page_idle_get_page(pfn);
+		if (page) {
+			if (page_is_idle(page)) {
+				/*
+				 * The page might have been referenced via a
+				 * pte, in which case it is not idle. Clear
+				 * refs and recheck.
+				 */
+				page_idle_clear_pte_refs(page);
+				if (page_is_idle(page))
+					*out |= 1ULL << bit;
+			}
+			put_page(page);
+		}
+		if (bit == BITMAP_CHUNK_BITS - 1)
+			out++;
+		cond_resched();
+	}
+	return (char *)out - buf;
+}
+
+static ssize_t page_idle_bitmap_write(struct file *file, struct kobject *kobj,
+				      struct bin_attribute *attr, char *buf,
+				      loff_t pos, size_t count)
+{
+	const u64 *in = (u64 *)buf;
+	struct page *page;
+	unsigned long pfn, end_pfn;
+	int bit;
+
+	if (pos % BITMAP_CHUNK_SIZE || count % BITMAP_CHUNK_SIZE)
+		return -EINVAL;
+
+	pfn = pos * BITS_PER_BYTE;
+	if (pfn >= max_pfn)
+		return -ENXIO;
+
+	end_pfn = pfn + count * BITS_PER_BYTE;
+	if (end_pfn > max_pfn)
+		end_pfn = ALIGN(max_pfn, BITMAP_CHUNK_BITS);
+
+	for (; pfn < end_pfn; pfn++) {
+		bit = pfn % BITMAP_CHUNK_BITS;
+		if ((*in >> bit) & 1) {
+			page = page_idle_get_page(pfn);
+			if (page) {
+				page_idle_clear_pte_refs(page);
+				set_page_idle(page);
+				put_page(page);
+			}
+		}
+		if (bit == BITMAP_CHUNK_BITS - 1)
+			in++;
+		cond_resched();
+	}
+	return (char *)in - buf;
+}
+
+static struct bin_attribute page_idle_bitmap_attr =
+		__BIN_ATTR(bitmap, S_IRUSR | S_IWUSR,
+			   page_idle_bitmap_read, page_idle_bitmap_write, 0);
+
+static struct bin_attribute *page_idle_bin_attrs[] = {
+	&page_idle_bitmap_attr,
+	NULL,
+};
+
+static struct attribute_group page_idle_attr_group = {
+	.bin_attrs = page_idle_bin_attrs,
+	.name = "page_idle",
+};
+
+static int __init page_idle_init(void)
+{
+	int err;
+
+	err = sysfs_create_group(mm_kobj, &page_idle_attr_group);
+	if (err) {
+		pr_err("page_idle: register sysfs failed\n");
+		return err;
+	}
+	return 0;
+}
+subsys_initcall(page_idle_init);
diff --git a/mm/rmap.c b/mm/rmap.c
index d68b07192167..5039034a0bb0 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -57,6 +57,7 @@
 #include <linux/migrate.h>
 #include <linux/hugetlb.h>
 #include <linux/backing-dev.h>
+#include <linux/page_idle.h>
 
 #include <asm/tlbflush.h>
 
@@ -723,6 +724,11 @@ int page_referenced_one(struct page *page, struct vm_area_struct *vma,
 		pte_unmap_unlock(pte, ptl);
 	}
 
+	if (referenced)
+		clear_page_idle(page);
+	if (test_and_clear_page_young(page))
+		referenced++;
+
 	(*mapcount)--;
 
 	if (referenced)
diff --git a/mm/swap.c b/mm/swap.c
index 89a690aa958f..68dd2895c2f4 100644
--- a/mm/swap.c
+++ b/mm/swap.c
@@ -31,6 +31,7 @@
 #include <linux/memcontrol.h>
 #include <linux/gfp.h>
 #include <linux/uio.h>
+#include <linux/page_idle.h>
 
 #include "internal.h"
 
@@ -612,6 +613,8 @@ void mark_page_accessed(struct page *page)
 	} else if (!PageReferenced(page)) {
 		SetPageReferenced(page);
 	}
+	if (page_is_idle(page))
+		clear_page_idle(page);
 }
 EXPORT_SYMBOL(mark_page_accessed);
 
-- 
2.1.4