2 files changed, 99 insertions, 16 deletions

diff --git a/fs/proc/base.c b/fs/proc/base.c
index 989af5e55d1b..ec158dd02b3a 100644
--- a/fs/proc/base.c
+++ b/fs/proc/base.c
@@ -715,6 +715,40 @@ static const struct file_operations proc_oom_adjust_operations = {
         .write          = oom_adjust_write,
 };
 
+static ssize_t clear_refs_write(struct file *file, const char __user *buf,
+                                size_t count, loff_t *ppos)
+{
+        struct task_struct *task;
+        char buffer[PROC_NUMBUF], *end;
+        struct mm_struct *mm;
+
+        memset(buffer, 0, sizeof(buffer));
+        if (count > sizeof(buffer) - 1)
+                count = sizeof(buffer) - 1;
+        if (copy_from_user(buffer, buf, count))
+                return -EFAULT;
+        if (!simple_strtol(buffer, &end, 0))
+                return -EINVAL;
+        if (*end == '\n')
+                end++;
+        task = get_proc_task(file->f_path.dentry->d_inode);
+        if (!task)
+                return -ESRCH;
+        mm = get_task_mm(task);
+        if (mm) {
+                clear_refs_smap(mm);
+                mmput(mm);
+        }
+        put_task_struct(task);
+        if (end - buffer == 0)
+                return -EIO;
+        return end - buffer;
+}
+
+static struct file_operations proc_clear_refs_operations = {
+        .write          = clear_refs_write,
+};
+
 #ifdef CONFIG_AUDITSYSCALL
 #define TMPBUFLEN 21
 static ssize_t proc_loginuid_read(struct file * file, char __user * buf,
@@ -1851,6 +1885,7 @@ static struct pid_entry tgid_base_stuff[] = {
         REG("mounts",     S_IRUGO, mounts),
         REG("mountstats", S_IRUSR, mountstats),
 #ifdef CONFIG_MMU
+        REG("clear_refs", S_IWUSR, clear_refs),
         REG("smaps",      S_IRUGO, smaps),
 #endif
 #ifdef CONFIG_SECURITY
@@ -2132,6 +2167,7 @@ static struct pid_entry tid_base_stuff[] = {
         LNK("exe",       exe),
         REG("mounts",    S_IRUGO, mounts),
 #ifdef CONFIG_MMU
+        REG("clear_refs", S_IWUSR, clear_refs),
         REG("smaps",     S_IRUGO, smaps),
 #endif
 #ifdef CONFIG_SECURITY
diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
index 199088ee969b..4008c060f7ef 100644
--- a/fs/proc/task_mmu.c
+++ b/fs/proc/task_mmu.c
@@ -195,7 +195,7 @@ static int show_map_internal(struct seq_file *m, void *v, struct mem_size_stats
                            "Shared_Dirty:   %8lu kB\n"
                            "Private_Clean:  %8lu kB\n"
                            "Private_Dirty:  %8lu kB\n"
-                           "Pgs_Referenced: %8lu kB\n",
+                           "Referenced:     %8lu kB\n",
                            (vma->vm_end - vma->vm_start) >> 10,
                            mss->resident >> 10,
                            mss->shared_clean  >> 10,
@@ -214,9 +214,9 @@ static int show_map(struct seq_file *m, void *v)
         return show_map_internal(m, v, NULL);
 }
 
-static void smaps_one_pmd(struct vm_area_struct *vma, pmd_t *pmd,
-                          unsigned long addr, unsigned long end,
-                          void *private)
+static void smaps_pte_range(struct vm_area_struct *vma, pmd_t *pmd,
+                            unsigned long addr, unsigned long end,
+                            void *private)
 {
         struct mem_size_stats *mss = private;
         pte_t *pte, ptent;
@@ -254,8 +254,34 @@ static void smaps_one_pmd(struct vm_area_struct *vma, pmd_t *pmd,
         cond_resched();
 }
 
-static inline void for_each_pmd_in_pud(struct pmd_walker *walker, pud_t *pud,
-                                       unsigned long addr, unsigned long end)
+static void clear_refs_pte_range(struct vm_area_struct *vma, pmd_t *pmd,
+                                 unsigned long addr, unsigned long end,
+                                 void *private)
+{
+        pte_t *pte, ptent;
+        spinlock_t *ptl;
+        struct page *page;
+
+        pte = pte_offset_map_lock(vma->vm_mm, pmd, addr, &ptl);
+        for (; addr != end; pte++, addr += PAGE_SIZE) {
+                ptent = *pte;
+                if (!pte_present(ptent))
+                        continue;
+
+                page = vm_normal_page(vma, addr, ptent);
+                if (!page)
+                        continue;
+
+                /* Clear accessed and referenced bits. */
+                ptep_test_and_clear_young(vma, addr, pte);
+                ClearPageReferenced(page);
+        }
+        pte_unmap_unlock(pte - 1, ptl);
+        cond_resched();
+}
+
+static inline void walk_pmd_range(struct pmd_walker *walker, pud_t *pud,
+                                  unsigned long addr, unsigned long end)
 {
         pmd_t *pmd;
         unsigned long next;
@@ -269,8 +295,8 @@ static inline void for_each_pmd_in_pud(struct pmd_walker *walker, pud_t *pud,
         }
 }
 
-static inline void for_each_pud_in_pgd(struct pmd_walker *walker, pgd_t *pgd,
-                                       unsigned long addr, unsigned long end)
+static inline void walk_pud_range(struct pmd_walker *walker, pgd_t *pgd,
+                                  unsigned long addr, unsigned long end)
 {
         pud_t *pud;
         unsigned long next;
@@ -280,15 +306,24 @@ static inline void for_each_pud_in_pgd(struct pmd_walker *walker, pgd_t *pgd,
                 next = pud_addr_end(addr, end);
                 if (pud_none_or_clear_bad(pud))
                         continue;
-                for_each_pmd_in_pud(walker, pud, addr, next);
+                walk_pmd_range(walker, pud, addr, next);
         }
 }
 
-static inline void for_each_pmd(struct vm_area_struct *vma,
-                                void (*action)(struct vm_area_struct *, pmd_t *,
-                                               unsigned long, unsigned long,
-                                               void *),
-                                void *private)
+/*
+ * walk_page_range - walk the page tables of a VMA with a callback
+ * @vma - VMA to walk
+ * @action - callback invoked for every bottom-level (PTE) page table
+ * @private - private data passed to the callback function
+ *
+ * Recursively walk the page table for the memory area in a VMA, calling
+ * a callback for every bottom-level (PTE) page table.
+ */
+static inline void walk_page_range(struct vm_area_struct *vma,
+                                   void (*action)(struct vm_area_struct *,
+                                                  pmd_t *, unsigned long,
+                                                  unsigned long, void *),
+                                   void *private)
 {
         unsigned long addr = vma->vm_start;
         unsigned long end = vma->vm_end;
@@ -305,7 +340,7 @@ static inline void for_each_pmd(struct vm_area_struct *vma,
                 next = pgd_addr_end(addr, end);
                 if (pgd_none_or_clear_bad(pgd))
                         continue;
-                for_each_pud_in_pgd(&walker, pgd, addr, next);
+                walk_pud_range(&walker, pgd, addr, next);
         }
 }
 
@@ -316,10 +351,22 @@ static int show_smap(struct seq_file *m, void *v)
 
         memset(&mss, 0, sizeof mss);
         if (vma->vm_mm && !is_vm_hugetlb_page(vma))
-                for_each_pmd(vma, smaps_one_pmd, &mss);
+                walk_page_range(vma, smaps_pte_range, &mss);
         return show_map_internal(m, v, &mss);
 }
 
+void clear_refs_smap(struct mm_struct *mm)
+{
+        struct vm_area_struct *vma;
+
+        down_read(&mm->mmap_sem);
+        for (vma = mm->mmap; vma; vma = vma->vm_next)
+                if (vma->vm_mm && !is_vm_hugetlb_page(vma))
+                        walk_page_range(vma, clear_refs_pte_range, NULL);
+        flush_tlb_mm(mm);
+        up_read(&mm->mmap_sem);
+}
+
 static void *m_start(struct seq_file *m, loff_t *pos)
 {
         struct proc_maps_private *priv = m->private;