[PATCH 1/1] pagemap clear_refs: modify to specify anon or mapped vma clearing

["Moussa A. Ba" <moussa.a.ba@gmail.com>]

This patch adds anonymous and file backed filters to the clear_refs interface.
echo 1 > /proc/PID/clear_refs resets the bits on all pages
echo 2 > /proc/PID/clear_refs resets the bits on anonymous pages only
echo 3 > /proc/PID/clear_refs resets the bits on file backed pages only
Any other value is ignored.

---
Signed-off-by: Moussa A. Ba <moussa.a.ba@gmail.com>
Signed-off-by: Jared E. Hulbert <jaredeh@gmail.com>
--- a/Documentation/filesystems/proc.txt	2009-07-20 17:29:11.000000000 -0700
+++ b/Documentation/filesystems/proc.txt	2009-07-27 16:58:05.000000000 -0700
@@ -375,6 +375,18 @@ of memory currently marked as referenced
  This file is only present if the CONFIG_MMU kernel configuration option is
  enabled.

+The /proc/PID/clear_refs is used to reset the PG_Referenced and ACCESSED/YOUNG
+bits on both physical and virtual pages associated with a process.
+To clear the bits for all the pages associated with the process
+    > echo 1 > /proc/PID/clear_refs
+
+To clear the bits for the anonymous pages associated with the process
+    > echo 2 > /proc/PID/clear_refs
+
+To clear the bits for the file backed pages associated with the process
+    > echo 3 > /proc/PID/clear_refs
+Any other value written to /proc/PID/clear_refs will have no effect.
+
  1.2 Kernel data
  ---------------

--- a/fs/proc/task_mmu.c	2009-07-21 14:30:01.000000000 -0700
+++ b/fs/proc/task_mmu.c	2009-07-27 17:05:25.000000000 -0700
@@ -462,6 +462,10 @@ static int clear_refs_pte_range(pmd_t *
  	return 0;
  }

+#define CLEAR_REFS_ALL 1
+#define CLEAR_REFS_ANON 2
+#define CLEAR_REFS_MAPPED 3
+
  static ssize_t clear_refs_write(struct file *file, const char __user * buf,
  				size_t count, loff_t * ppos)
  {
@@ -469,13 +473,15 @@ static ssize_t clear_refs_write(struct f
  	char buffer[PROC_NUMBUF], *end;
  	struct mm_struct *mm;
  	struct vm_area_struct *vma;
+	int type;

  	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))
+	type = simple_strtol(buffer, &end, 0);
+	if (!type || type < CLEAR_REFS_ALL || type > CLEAR_REFS_MAPPED)
  		return -EINVAL;
  	if (*end == '\n')
  		end++;
@@ -491,9 +497,23 @@ static ssize_t clear_refs_write(struct f
  		down_read(&mm->mmap_sem);
  		for (vma = mm->mmap; vma; vma = vma->vm_next) {
  			clear_refs_walk.private = vma;
-			if (!is_vm_hugetlb_page(vma))
-				walk_page_range(vma->vm_start, vma->vm_end,
-						&clear_refs_walk);
+			if (is_vm_hugetlb_page(vma))
+				continue;
+			/*
+			 * Writing 1 to /proc/pid/clear_refs affects all pages.
+			 *
+			 * Writing 2 to /proc/pid/clear_refs only affects
+			 * Anonymous pages.
+			 *
+			 * Writing 3 to /proc/pid/clear_refs only affects file
+			 * backed pages.
+			 */
+			if (type == CLEAR_REFS_ANON && vma->vm_file)
+				continue;
+			if (type == CLEAR_REFS_MAPPED && !vma->vm_file)
+				continue;
+			walk_page_range(vma->vm_start, vma->vm_end,
+					&clear_refs_walk);
  		}
  		flush_tlb_mm(mm);
  		up_read(&mm->mmap_sem);