smaps: add clear_refs file to clear reference

Adds /proc/pid/clear_refs.  When any non-zero number is written to this file,
pte_mkold() and ClearPageReferenced() is called for each pte and its
corresponding page, respectively, in that task's VMAs.  This file is only
writable by the user who owns the task.

It is now possible to measure _approximately_ how much memory a task is using
by clearing the reference bits with

	echo 1 > /proc/pid/clear_refs

and checking the reference count for each VMA from the /proc/pid/smaps output
at a measured time interval.  For example, to observe the approximate change
in memory footprint for a task, write a script that clears the references
(echo 1 > /proc/pid/clear_refs), sleeps, and then greps for Pgs_Referenced and
extracts the size in kB.  Add the sizes for each VMA together for the total
referenced footprint.  Moments later, repeat the process and observe the
difference.

For example, using an efficient Mozilla:

	accumulated time		referenced memory
	----------------		-----------------
		 0 s				 408 kB
		 1 s				 408 kB
		 2 s				 556 kB
		 3 s				1028 kB
		 4 s				 872 kB
		 5 s				1956 kB
		 6 s				 416 kB
		 7 s				1560 kB
		 8 s				2336 kB
		 9 s				1044 kB
		10 s				 416 kB

This is a valuable tool to get an approximate measurement of the memory
footprint for a task.

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>
[akpm@linux-foundation.org: build fixes]
[mpm@selenic.com: rename for_each_pmd]
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 63 insertions, 16 deletions

diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
index 199088ee969..4008c060f7e 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;