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--- proc:smaps_file [2017/04/05 09:53] – peter
+++ proc:smaps_file [2020/07/15 09:30] (current) – external edit 127.0.0.1
@@ Line 1: / Line 1: @@
 ====== Proc - smaps file ======
+The **/proc/PID/smaps** is an extension based on maps, showing the memory consumption for each of the process's mappings.  This file is only present if the **CONFIG_MMU** kernel configuration option is enabled.
 For SMP CONFIG users.
-For making accounting scalable, RSS related information are handled in asynchronous manner and the value may not be very precise.  To see a precise snapshot of a moment, you can see /proc/<pid>/smaps file and scan page table.  It's slow but very precise.
+For making accounting scalable, RSS related information are handled in asynchronous manner and the value may not be very precise.  To see a precise snapshot of a moment, you can see **/proc/<pid>/smaps** file and scan page table.  It's slow but very precise.
+For each of mappings there is a series of lines such as the following:
+^address^perms^offset^dev^inode^pathname^
+|08048000-080bc000|r-xp|00000000|03:02|13130|/bin/bash|
+This shows the same information as is displayed for the mapping in [[Proc:maps file|/proc/PID/maps]].
+Additional information is also shown:
+|Size:|1084 kB|
+|Rss:|892 kB|
+|Pss:|374 kB|
+|Shared_Clean:|892 kB|
+|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|
+where:
+  * **Size** is the size of the mapping.
+  * **RSS** is the amount of the mapping that is currently resident in RAM.
+  * **PSS** is the process' proportional share of this mapping.
+  * **Shared_Clean** is the number of clean shared pages in the mapping.
+  * **Shared_Dirty** is the number of dirty shared pages in the mapping.
+  * **Private_Clean** is the number of clean private pages in the mapping.
+  * **Private_Dirty** is the number of dirty private pages in the mapping.
+  * **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.
+**NOTE:**  Even a page which is part of a **MAP_SHARED** mapping, but which only has a single private mapped, i.e. is currently used by only one process, is accounted as __private__ and not as shared.