mm: count swap usage

A frequent questions from users about memory management is what numbers of
swap ents are user for processes.  And this information will give some
hints to oom-killer.

Besides we can count the number of swapents per a process by scanning
/proc/<pid>/smaps, this is very slow and not good for usual process
information handler which works like 'ps' or 'top'.  (ps or top is now
enough slow..)

This patch adds a counter of swapents to mm_counter and update is at each
swap events.  Information is exported via /proc/<pid>/status file as

[kamezawa@bluextal memory]$ cat /proc/self/status
Name:   cat
State:  R (running)
Tgid:   2910
Pid:    2910
PPid:   2823
TracerPid:      0
Uid:    500     500     500     500
Gid:    500     500     500     500
FDSize: 256
Groups: 500
VmPeak:    82696 kB
VmSize:    82696 kB
VmLck:         0 kB
VmHWM:       432 kB
VmRSS:       432 kB
VmData:      172 kB
VmStk:        84 kB
VmExe:        48 kB
VmLib:      1568 kB
VmPTE:        40 kB
VmSwap:        0 kB <=============== this.

[akpm@linux-foundation.org: coding-style fixes]
Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Reviewed-by: Minchan Kim <minchan.kim@gmail.com>
Reviewed-by: Christoph Lameter <cl@linux-foundation.org>
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: David Rientjes <rientjes@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 2 insertions, 0 deletions

diff --git a/Documentation/filesystems/proc.txt b/Documentation/filesystems/proc.txt
index e418f3d8f427..b5c5fc657a88 100644
--- a/Documentation/filesystems/proc.txt
+++ b/Documentation/filesystems/proc.txt
@@ -164,6 +164,7 @@ read the file /proc/PID/status:
   VmExe:        68 kB
   VmLib:      1412 kB
   VmPTE:        20 kb
+  VmSwap:        0 kB
   Threads:        1
   SigQ:   0/28578
   SigPnd: 0000000000000000
@@ -219,6 +220,7 @@ Table 1-2: Contents of the statm files (as of 2.6.30-rc7)
  VmExe                       size of text segment
  VmLib                       size of shared library code
  VmPTE                       size of page table entries
+ VmSwap                      size of swap usage (the number of referred swapents)
  Threads                     number of threads
  SigQ                        number of signals queued/max. number for queue
  SigPnd                      bitmap of pending signals for the thread