Re: [PATCH v2] Document the new Anonymous field in smaps.

[Hugh Dickins]

On Fri, 17 Sep 2010, Nikanth Karthikesan wrote:
> Document the new Anonymous field in smaps.

Thanks for doing that, good effort, but your shifts between singular
and plural rather jarred on my ear, so I've rewritten it a little below.
Also added a sentence on "Swap"; but gave up when it came to KernelPageSize
and MMUPageSize, let someone else clarify those later.


[PATCH v3] Document the new Anonymous field in smaps.

From: Nikanth Karthikesan <knikanth@xxxxxxx>

Document the new Anonymous field in smaps, and also the Swap field.
Explain what smaps means by shared and private, which differs from
MAP_SHARED and MAP_PRIVATE.

Signed-off-by: Nikanth Karthikesan <knikanth@xxxxxxx>
Signed-off-by: Hugh Dickins <hughd@xxxxxxxxxx>
---

 Documentation/filesystems/proc.txt |   15 +++++++++++----
 1 file changed, 11 insertions(+), 4 deletions(-)

--- a/Documentation/filesystems/proc.txt
+++ b/Documentation/filesystems/proc.txt
@@ -370,17 +370,24 @@ Shared_Dirty:          0 kB
 Private_Clean:         0 kB
 Private_Dirty:         0 kB
 Referenced:          892 kB
+Anonymous:             0 kB
 Swap:                  0 kB
 KernelPageSize:        4 kB
 MMUPageSize:           4 kB
 
-The first  of these lines shows  the same information  as is displayed for the
-mapping in /proc/PID/maps.  The remaining lines show  the size of the mapping,
+The first of these lines shows the same information as is displayed for the
+mapping in /proc/PID/maps. The remaining lines show the size of the mapping,
 the amount of the mapping that is currently resident in RAM, the "proportional
 set sizeâ (divide each shared page by the number of processes sharing it), the
 number of clean and dirty shared pages in the mapping, and the number of clean
-and dirty private pages in the mapping.  The "Referenced" indicates the amount
-of memory currently marked as referenced or accessed.
+and dirty private pages in the mapping. Note that even a page which is part of
+a MAP_SHARED mapping, but has only a single pte mapped, i.e. is currently used
+by only one process, is accounted as private and not as shared. "Referenced"
+indicates the amount of memory currently marked as referenced or accessed.
+"Anonymous" shows the amount of memory that does not belong to any file. Even
+a mapping associated with a file may contain anonymous pages: when MAP_PRIVATE
+and a page is modified, the file page is replaced by a private anonymous copy.
+"Swap" shows how much would-be-anonymous memory is also used, but out on swap.
 
 This file is only present if the CONFIG_MMU kernel configuration option is
 enabled.