smaps: add pages referenced count to smaps

Adds an additional unsigned long field to struct mem_size_stats called
'referenced'.  For each pte walked in the smaps code, this field is
incremented by PAGE_SIZE if it has pte-reference bits.

An additional line was added to the /proc/pid/smaps output for each VMA to
indicate how many pages within it are currently marked as referenced or
accessed.

Cc: Hugh Dickins <hugh@veritas.com>
Cc: Paul Mundt <lethal@linux-sh.org>
Cc: Christoph Lameter <clameter@sgi.com>
Signed-off-by: David Rientjes <rientjes@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

fs/proc/task_mmu.c

@@ -120,6 +120,7 @@ struct mem_size_stats
 	unsigned long shared_dirty;
 	unsigned long private_clean;
 	unsigned long private_dirty;
+	unsigned long referenced;
 };
 
 struct pmd_walker {
@@ -193,13 +194,15 @@ static int show_map_internal(struct seq_file *m, void *v, struct mem_size_stats
 			   "Shared_Clean:   %8lu kB\n"
 			   "Shared_Dirty:   %8lu kB\n"
 			   "Private_Clean:  %8lu kB\n"
-			   "Private_Dirty: %8lu kB\n",
+			   "Private_Dirty:  %8lu kB\n"
+			   "Pgs_Referenced: %8lu kB\n",
 			   (vma->vm_end - vma->vm_start) >> 10,
 			   mss->resident >> 10,
 			   mss->shared_clean  >> 10,
 			   mss->shared_dirty  >> 10,
 			   mss->private_clean >> 10,
-			   mss->private_dirty >> 10);
+			   mss->private_dirty >> 10,
+			   mss->referenced >> 10);
 
 	if (m->count < m->size)  /* vma is copied successfully */
 		m->version = (vma != get_gate_vma(task))? vma->vm_start: 0;
@@ -232,6 +235,9 @@ static void smaps_one_pmd(struct vm_area_struct *vma, pmd_t *pmd,
 		if (!page)
 			continue;
 
+		/* Accumulate the size in pages that have been accessed. */
+		if (pte_young(ptent) || PageReferenced(page))
+			mss->referenced += PAGE_SIZE;
 		if (page_mapcount(page) >= 2) {
 			if (pte_dirty(ptent))
 				mss->shared_dirty += PAGE_SIZE;