mm, procfs: breakdown RSS for anon, shmem and file in /proc/pid/status

There are several shortcomings with the accounting of shared memory
(SysV shm, shared anonymous mapping, mapping of a tmpfs file).  The
values in /proc/<pid>/status and <...>/statm don't allow to distinguish
between shmem memory and a shared mapping to a regular file, even though
theirs implication on memory usage are quite different: during reclaim,
file mapping can be dropped or written back on disk, while shmem needs a
place in swap.

Also, to distinguish the memory occupied by anonymous and file mappings,
one has to read the /proc/pid/statm file, which has a field for the file
mappings (again, including shmem) and total memory occupied by these
mappings (i.e.  equivalent to VmRSS in the <...>/status file.  Getting
the value for anonymous mappings only is thus not exactly user-friendly
(the statm file is intended to be rather efficiently machine-readable).

To address both of these shortcomings, this patch adds a breakdown of
VmRSS in /proc/<pid>/status via new fields RssAnon, RssFile and
RssShmem, making use of the previous preparatory patch.  These fields
tell the user the memory occupied by private anonymous pages, mapped
regular files and shmem, respectively.  Other existing fields in /status
and /statm files are left without change.  The /statm file can be
extended in the future, if there's a need for that.

Example (part of) /proc/pid/status output including the new Rss* fields:

VmPeak:  2001008 kB
VmSize:  2001004 kB
VmLck:         0 kB
VmPin:         0 kB
VmHWM:      5108 kB
VmRSS:      5108 kB
RssAnon:              92 kB
RssFile:            1324 kB
RssShmem:           3692 kB
VmData:      192 kB
VmStk:       136 kB
VmExe:         4 kB
VmLib:      1784 kB
VmPTE:      3928 kB
VmPMD:        20 kB
VmSwap:        0 kB
HugetlbPages:          0 kB

[vbabka@suse.cz: forward-porting, tweak changelog]
Signed-off-by: Jerome Marchand <jmarchan@redhat.com>
Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
Acked-by: Konstantin Khlebnikov <khlebnikov@yandex-team.ru>
Acked-by: Michal Hocko <mhocko@suse.com>
Acked-by: Hugh Dickins <hughd@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 11 insertions, 2 deletions

diff --git a/Documentation/filesystems/proc.txt b/Documentation/filesystems/proc.txt
index fdeb5b33349f..ffcd49589ab5 100644
--- a/Documentation/filesystems/proc.txt
+++ b/Documentation/filesystems/proc.txt
@@ -169,6 +169,9 @@ read the file /proc/PID/status:
   VmLck:         0 kB
   VmHWM:       476 kB
   VmRSS:       476 kB
+  RssAnon:             352 kB
+  RssFile:             120 kB
+  RssShmem:              4 kB
   VmData:      156 kB
   VmStk:        88 kB
   VmExe:        68 kB
@@ -231,7 +234,12 @@ Table 1-2: Contents of the status files (as of 4.1)
  VmSize                      total program size
  VmLck                       locked memory size
  VmHWM                       peak resident set size ("high water mark")
- VmRSS                       size of memory portions
+ VmRSS                       size of memory portions. It contains the three
+                             following parts (VmRSS = RssAnon + RssFile + RssShmem)
+ RssAnon                     size of resident anonymous memory
+ RssFile                     size of resident file mappings
+ RssShmem                    size of resident shmem memory (includes SysV shm,
+                             mapping of tmpfs and shared anonymous mappings)
  VmData                      size of data, stack, and text segments
  VmStk                       size of data, stack, and text segments
  VmExe                       size of text segment
@@ -266,7 +274,8 @@ Table 1-3: Contents of the statm files (as of 2.6.8-rc3)
  Field    Content
  size     total program size (pages)		(same as VmSize in status)
  resident size of memory portions (pages)	(same as VmRSS in status)
- shared   number of pages that are shared	(i.e. backed by a file)
+ shared   number of pages that are shared	(i.e. backed by a file, same
+						as RssFile+RssShmem in status)
  trs      number of pages that are 'code'	(not including libs; broken,
 							includes data segment)
  lrs      number of pages of library		(always 0 on 2.6)