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, 36 insertions, 0 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